* Re: [PATCH v3 09/30] liveupdate: kho: move to kernel/liveupdate
From: Pasha Tatashin @ 2025-09-22 14:54 UTC (permalink / raw)
To: Mike Rapoport
Cc: pratyush, jasonmiu, graf, changyuanl, dmatlack, rientjes, corbet,
rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm,
tj, yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, zhangguopeng,
linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu
In-Reply-To: <aLK3trXYYYIUaV4Q@kernel.org>
On Sat, Aug 30, 2025 at 4:35 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Thu, Aug 07, 2025 at 01:44:15AM +0000, Pasha Tatashin wrote:
> > Move KHO to kernel/liveupdate/ in preparation of placing all Live Update
> > core kernel related files to the same place.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> >
> > ---
> > diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile
> > new file mode 100644
> > index 000000000000..72cf7a8e6739
> > --- /dev/null
> > +++ b/kernel/liveupdate/Makefile
> > @@ -0,0 +1,7 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +#
> > +# Makefile for the linux kernel.
>
> Nit: this line does not provide much, let's drop it
Done.
Thank you,
Pasha
^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Nicolas Schichan @ 2025-09-22 14:28 UTC (permalink / raw)
To: Askar Safin
Cc: akpm, andy.shevchenko, axboe, brauner, cyphar, devicetree,
ecurtin, email2tema, graf, gregkh, hca, hch, hsiangkao, initramfs,
jack, julian.stecklina, kees, linux-acpi, linux-alpha, linux-api,
linux-arch, linux-arm-kernel, linux-block, linux-csky, linux-doc,
linux-efi, linux-ext4, linux-fsdevel, linux-hexagon, linux-kernel,
linux-m68k, linux-mips, linux-openrisc, linux-parisc, linux-riscv,
linux-s390, linux-sh, linux-snps-arc, linux-um, linuxppc-dev,
loongarch, mcgrof, mingo, monstr, mzxreary, patches, rob,
sparclinux, thomas.weissschuh, thorsten.blum, torvalds, tytso,
viro, x86
In-Reply-To: <CAPnZJGDwETQVVURezSRxZB8ZAwBETQ5fwbXyeMpfDLuLW4rVdg@mail.gmail.com>
[resending to the lists and Cc, sorry I initially replied only to Askar]
On Sat, Sep 20, 2025 at 5:55 AM Askar Safin <safinaskar@gmail.com> wrote:
> On Fri, Sep 19, 2025 at 6:25 PM Nicolas Schichan <nschichan@freebox.fr> wrote:
> > Considering that the deprecation message didn't get displayed in some
> > configurations, maybe it's a bit early at the very least.
>
> I changed my opinion.
> Breaking users, who did not see a deprecation message at all,
> is unfair.
> I will send a patchset soon, which will remove initrd codepath,
> which currently contains deprecation notice. And I will put
> deprecation notice to
> other codepath.
Thanks
> Then in September 2026 I will fully remove initrd.
Is there a way to find some kind of middle ground here ?
I'm lead to believe that the main issue with the current code is that
it needs to parse the superblocks of the ramdisk image in order to get
the amount to data to copy into /dev/ram0.
It looks like it is partly because of the ramdisk_start= kernel
command line parameter which looks to be a remnant of the time it was
possible to boot on floppy disk on x86.
This kernel command line allows to look for a rootfs image at an
offset into the initrd data.
If we assume now that the rootfs image data starts at the beginning of
the initrd image and is the only part of the initrd image this would
indeed remove a lot of complexity.
Maybe it would be possible to remove the identify_ramdisk_image()
function and just copy the actual size of /initrd.image into
/dev/ram0. This would allow any file system to be used in an initrd
image (no just romfs, cramfs, minixfs, ext2fs and squashfs), and this
would simplify the code in init/do_mounts_rd.c greatly, with just the
function rd_load_image() and nr_blocks() remaining in this file.
I can send a patch for that but first I need to sort out my SMTP
issues from the other day.
Regards,
--
Nicolas Schichan
^ permalink raw reply
* Re: [PATCH v4 07/10] man/man2/open_tree.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-22 13:22 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-09-22-sneaky-similar-mind-cilantro-u1EJJ2@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 1748 bytes --]
Hi Aleksa,
On Mon, Sep 22, 2025 at 08:09:47PM +1000, Aleksa Sarai wrote:
> > > +is lazy\[em]akin to calling
> >
> > I prefer em dashes in both sides of the parenthetical; it more clearly
> > denotes where it ends.
> >
> > is lazy
> > \[em]akin to calling
> > .BR umount2 (2)
> > with
> > .BR MOUNT_DETACH \[em];
>
> An \[em] next to a ";"? Let me see if I can rewrite it to avoid this...
You could use parentheses, maybe.
> > > +.IR "mount --bind" )
> >
> > You need to escape dashes in manual pages. Otherwise, they're formatted
> > as hyphens, which can't be pasted into the terminal (and another
> > consequence is not being able to search for them in the man(1) reader
> > with literal dashes).
> >
> > Depending on your system, you might be able to search for them or paste
> > them to the terminal, because some distros patch this in
> > /etc/local/an.tmac, at the expense of generating lower quality pages,
> > but in general don't rely on that.
> >
> > I've noticed now, but this probably also happens in previous pages in
> > this patch set.
> >
> > While at it, you should also use a non-breaking space, to keep the
> > entire command in the same line.
> >
> > .IR \%mount\~\-\-bind )
>
> My bad, I think my terminal font doesn't distinguish between them well
> enough for it to be obvious. I'll go through and fix up all of these
> cases.
I should probably add an automated diagnostic. At least the case of two
'--' together, which I've never seen useful unescaped, should be
diagnosed. I'll add a make(1) 'lint-man-dash' target that catches this
with a regex.
Have a lovely day!
Alex
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 07/10] man/man2/open_tree.2: document "new" mount API
From: Aleksa Sarai @ 2025-09-22 10:09 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <gyhtwwu7kgkaz5l5h46ll3voypfk74cahpfpmagbngj3va3x7c@pm3pssyst2al>
[-- Attachment #1: Type: text/plain, Size: 17051 bytes --]
On 2025-09-21, Alejandro Colomar <alx@kernel.org> wrote:
> Hi Aleksa,
>
> On Fri, Sep 19, 2025 at 11:59:48AM +1000, Aleksa Sarai wrote:
> > This is loosely based on the original documentation written by David
> > Howells and later maintained by Christian Brauner, but has been
> > rewritten to be more from a user perspective (as well as fixing a few
> > critical mistakes).
> >
> > Co-authored-by: David Howells <dhowells@redhat.com>
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > Co-authored-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> > ---
> > man/man2/open_tree.2 | 498 +++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 498 insertions(+)
> >
> > diff --git a/man/man2/open_tree.2 b/man/man2/open_tree.2
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..7f85df08b43c7b48a9d021dbbeb2c60092a2b2d4
> > --- /dev/null
> > +++ b/man/man2/open_tree.2
> > @@ -0,0 +1,498 @@
> > +.\" Copyright, the authors of the Linux man-pages project
> > +.\"
> > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> > +.\"
> > +.TH open_tree 2 (date) "Linux man-pages (unreleased)"
> > +.SH NAME
> > +open_tree \- open path or create detached mount object and attach to fd
> > +.SH LIBRARY
> > +Standard C library
> > +.RI ( libc ,\~ \-lc )
> > +.SH SYNOPSIS
> > +.nf
> > +.BR "#define _GNU_SOURCE " "/* See feature_test_macros(7) */"
> > +.BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */"
> > +.B #include <sys/mount.h>
> > +.P
> > +.BI "int open_tree(int " dirfd ", const char *" path ", unsigned int " flags );
> > +.fi
> > +.SH DESCRIPTION
> > +The
> > +.BR open_tree ()
> > +system call is part of
> > +the suite of file descriptor based mount facilities in Linux.
> > +.IP \[bu] 3
> > +If
> > +.I flags
> > +contains
> > +.BR \%OPEN_TREE_CLONE ,
> > +.BR open_tree ()
> > +creates a detached mount object
> > +which consists of a bind-mount of
> > +the path specified by the
> > +.IR path .
> > +A new file descriptor
> > +associated with the detached mount object
> > +is then returned.
> > +The mount object is equivalent to a bind-mount
> > +that would be created by
> > +.BR mount (2)
> > +called with
> > +.BR MS_BIND ,
> > +except that it is tied to a file descriptor
> > +and is not mounted onto the filesystem.
> > +.IP
> > +As with file descriptors returned from
> > +.BR fsmount (2),
> > +the resultant file descriptor can then be used with
> > +.BR move_mount (2),
> > +.BR mount_setattr (2),
> > +or other such system calls to do further mount operations.
> > +This mount object will be unmounted and destroyed
> > +when the file descriptor is closed
> > +if it was not otherwise attached to a mount point
> > +by calling
> > +.BR move_mount (2).
> > +(Note that the unmount operation on
>
> Maybe I would make this note a paragraph of its own; this would give it
> more visibility, I think. And I'd remove 'Note that', and start
> directly with the noted contents (everything in a manual page must be
> noteworthy, in general).
>
> > +.BR close (2)
>
> I'm a bit confused by the reference to close(2). The previous text
> mentions closing, but not close(2), so I'm not sure if this refers to
> that or if it is comparing it to close(2). Would you mind having a look
> at the wording of this entire paragraph?
Well, it's more that these kinds of file descriptors are marked with
FMODE_NEEDS_UMOUNT which will cause dissolve_on_fput() to be called when
they have no more references.
So this could be through close(2) or any other condition that causes a
file descriptor to be closed (dup2(2), process death, execve with
O_CLOEXEC, etc). Maybe it's better to not mention close(2) explicitly...
> > +is lazy\[em]akin to calling
>
> I prefer em dashes in both sides of the parenthetical; it more clearly
> denotes where it ends.
>
> is lazy
> \[em]akin to calling
> .BR umount2 (2)
> with
> .BR MOUNT_DETACH \[em];
An \[em] next to a ";"? Let me see if I can rewrite it to avoid this...
> (I assume that's where it ends.)
>
> > +.BR umount2 (2)
> > +with
> > +.BR MOUNT_DETACH ;
> > +any existing open references to files
> > +from the mount object
> > +will continue to work,
> > +and the mount object will only be completely destroyed
> > +once it ceases to be busy.)
> > +.IP \[bu]
> > +If
> > +.I flags
> > +does not contain
> > +.BR \%OPEN_TREE_CLONE ,
> > +.BR open_tree ()
> > +returns a file descriptor
> > +that is exactly equivalent to
> > +one produced by
> > +.BR openat (2)
> > +when called with the same
> > +.I dirfd
> > +and
> > +.IR path .
> > +.P
> > +In either case, the resultant file descriptor
> > +acts the same as one produced by
> > +.BR open (2)
> > +with
> > +.BR O_PATH ,
> > +meaning it can also be used as a
> > +.I dirfd
> > +argument to
> > +"*at()" system calls.
> > +.P
> > +As with "*at()" system calls,
> > +.BR open_tree ()
> > +uses the
> > +.I dirfd
> > +argument in conjunction with the
> > +.I path
> > +argument to determine the path to operate on, as follows:
> > +.IP \[bu] 3
> > +If the pathname given in
> > +.I path
> > +is absolute, then
> > +.I dirfd
> > +is ignored.
> > +.IP \[bu]
> > +If the pathname given in
> > +.I path
> > +is relative and
> > +.I dirfd
> > +is the special value
> > +.BR \%AT_FDCWD ,
> > +then
> > +.I path
> > +is interpreted relative to
> > +the current working directory
> > +of the calling process (like
> > +.BR open (2)).
> > +.IP \[bu]
> > +If the pathname given in
> > +.I path
> > +is relative,
> > +then it is interpreted relative to
> > +the directory referred to by the file descriptor
> > +.I dirfd
> > +(rather than relative to
> > +the current working directory
> > +of the calling process,
> > +as is done by
> > +.BR open (2)
> > +for a relative pathname).
> > +In this case,
> > +.I dirfd
> > +must be a directory
> > +that was opened for reading
> > +.RB ( O_RDONLY )
> > +or using the
> > +.B O_PATH
> > +flag.
> > +.IP \[bu]
> > +If
> > +.I path
> > +is an empty string,
> > +and
> > +.I flags
> > +contains
> > +.BR \%AT_EMPTY_PATH ,
> > +then the file descriptor
> > +.I dirfd
> > +is operated on directly.
> > +In this case,
> > +.I dirfd
> > +may refer to any type of file,
> > +not just a directory.
> > +.P
> > +See
> > +.BR openat (2)
> > +for an explanation of why the
> > +.I dirfd
> > +argument is useful.
> > +.P
> > +.I flags
> > +can be used to control aspects of the path lookup
> > +and properties of the returned file descriptor.
> > +A value for
> > +.I flags
> > +is constructed by bitwise ORing
> > +zero or more of the following constants:
> > +.RS
> > +.TP
> > +.B \%AT_EMPTY_PATH
> > +If
> > +.I path
> > +is an empty string, operate on the file referred to by
> > +.I dirfd
> > +(which may have been obtained from
> > +.BR open (2),
> > +.BR fsmount(2),
> > +or from another
> > +.BR open_tree ()
> > +call).
> > +In this case,
> > +.I dirfd
> > +may refer to any type of file, not just a directory.
> > +If
> > +.I dirfd
> > +is
> > +.BR \%AT_FDCWD ,
> > +.BR open_tree ()
> > +will operate on the current working directory
> > +of the calling process.
> > +This flag is Linux-specific; define
> > +.B \%_GNU_SOURCE
> > +to obtain its definition.
> > +.TP
> > +.B \%AT_NO_AUTOMOUNT
> > +Do not automount the terminal ("basename") component of
> > +.I path
> > +if it is a directory that is an automount point.
> > +This allows you to create a handle to the automount point itself,
> > +rather than the location it would mount.
> > +This flag has no effect if the mount point has already been mounted over.
> > +This flag is Linux-specific; define
> > +.B \%_GNU_SOURCE
> > +to obtain its definition.
> > +.TP
> > +.B \%AT_SYMLINK_NOFOLLOW
> > +If
> > +.I path
> > +is a symbolic link, do not dereference it; instead,
> > +create either a handle to the link itself
> > +or a bind-mount of it.
> > +The resultant file descriptor is indistinguishable from one produced by
> > +.BR openat (2)
> > +with
> > +.BR \%O_PATH | O_NOFOLLLOW .
> > +.TP
> > +.B \%OPEN_TREE_CLOEXEC
> > +Set the close-on-exec
> > +.RB ( FD_CLOEXEC )
> > +flag on the new file descriptor.
> > +See the description of the
> > +.B O_CLOEXEC
> > +flag in
> > +.BR open (2)
> > +for reasons why this may be useful.
> > +.TP
> > +.B \%OPEN_TREE_CLONE
> > +Rather than creating an
> > +.BR openat (2)-style
> > +.B O_PATH
> > +file descriptor,
> > +create a bind-mount of
> > +.I path
> > +(akin to
> > +.IR "mount --bind" )
>
> You need to escape dashes in manual pages. Otherwise, they're formatted
> as hyphens, which can't be pasted into the terminal (and another
> consequence is not being able to search for them in the man(1) reader
> with literal dashes).
>
> Depending on your system, you might be able to search for them or paste
> them to the terminal, because some distros patch this in
> /etc/local/an.tmac, at the expense of generating lower quality pages,
> but in general don't rely on that.
>
> I've noticed now, but this probably also happens in previous pages in
> this patch set.
>
> While at it, you should also use a non-breaking space, to keep the
> entire command in the same line.
>
> .IR \%mount\~\-\-bind )
My bad, I think my terminal font doesn't distinguish between them well
enough for it to be obvious. I'll go through and fix up all of these
cases.
Thanks.
> Cheers,
> Alex
>
> > +as a detached mount object.
> > +In order to do this operation,
> > +the calling process must have the
> > +.BR \%CAP_SYS_ADMIN
> > +capability.
> > +.TP
> > +.B \%AT_RECURSIVE
> > +Create a recursive bind-mount of the path
> > +(akin to
> > +.IR "mount --rbind" )
> > +as a detached mount object.
> > +This flag is only permitted in conjunction with
> > +.BR \%OPEN_TREE_CLONE .
> > +.SH RETURN VALUE
> > +On success, a new file descriptor is returned.
> > +On error, \-1 is returned, and
> > +.I errno
> > +is set to indicate the error.
> > +.SH ERRORS
> > +.TP
> > +.B EACCES
> > +Search permission is denied for one of the directories
> > +in the path prefix of
> > +.IR path .
> > +(See also
> > +.BR path_resolution (7).)
> > +.TP
> > +.B EBADF
> > +.I path
> > +is relative but
> > +.I dirfd
> > +is neither
> > +.B \%AT_FDCWD
> > +nor a valid file descriptor.
> > +.TP
> > +.B EFAULT
> > +.I path
> > +is NULL
> > +or a pointer to a location
> > +outside the calling process's accessible address space.
> > +.TP
> > +.B EINVAL
> > +Invalid flag specified in
> > +.IR flags .
> > +.TP
> > +.B ELOOP
> > +Too many symbolic links encountered when resolving
> > +.IR path .
> > +.TP
> > +.B EMFILE
> > +The calling process has too many open files to create more.
> > +.TP
> > +.B ENAMETOOLONG
> > +.I path
> > +is longer than
> > +.BR PATH_MAX .
> > +.TP
> > +.B ENFILE
> > +The system has too many open files to create more.
> > +.TP
> > +.B ENOENT
> > +A component of
> > +.I path
> > +does not exist, or is a dangling symbolic link.
> > +.TP
> > +.B ENOENT
> > +.I path
> > +is an empty string, but
> > +.B AT_EMPTY_PATH
> > +is not specified in
> > +.IR flags .
> > +.TP
> > +.B ENOTDIR
> > +A component of the path prefix of
> > +.I path
> > +is not a directory, or
> > +.I path
> > +is relative and
> > +.I dirfd
> > +is a file descriptor referring to a file other than a directory.
> > +.TP
> > +.B ENOSPC
> > +The "anonymous" mount namespace
> > +necessary to contain the
> > +.B \%OPEN_TREE_CLONE
> > +detached bind-mount mount object
> > +could not be allocated,
> > +as doing so would exceed
> > +the configured per-user limit on
> > +the number of mount namespaces in the current user namespace.
> > +(See also
> > +.BR namespaces (7).)
> > +.TP
> > +.B ENOMEM
> > +The kernel could not allocate sufficient memory to complete the operation.
> > +.TP
> > +.B EPERM
> > +.I flags
> > +contains
> > +.B \%OPEN_TREE_CLONE
> > +but the calling process does not have the required
> > +.B CAP_SYS_ADMIN
> > +capability.
> > +.SH STANDARDS
> > +Linux.
> > +.SH HISTORY
> > +Linux 5.2.
> > +.\" commit a07b20004793d8926f78d63eb5980559f7813404
> > +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> > +glibc 2.36.
> > +.SH NOTES
> > +.SS Mount propagation
> > +The bind-mount mount objects created by
> > +.BR open_tree ()
> > +with
> > +.B \%OPEN_TREE_CLONE
> > +are not associated with
> > +the mount namespace of the calling process.
> > +Instead, each mount object is placed
> > +in a newly allocated "anonymous" mount namespace
> > +associated with the calling process.
> > +.P
> > +One of the side-effects of this is that
> > +(unlike bind-mounts created with
> > +.BR mount (2)),
> > +mount propagation
> > +(as described in
> > +.BR mount_namespaces (7))
> > +will not be applied to bind-mounts created by
> > +.BR open_tree ()
> > +until the bind-mount is attached with
> > +.BR move_mount (2),
> > +at which point the mount object
> > +will be associated with the mount namespace
> > +where it was attached
> > +and mount propagation will resume.
> > +Note that any mount propagation events that occurred
> > +before the mount object was attached
> > +will
> > +.I not
> > +be propagated to the mount object,
> > +even after it is attached.
> > +.SH EXAMPLES
> > +The following examples show how
> > +.BR open_tree ()
> > +can be used in place of more traditional
> > +.BR mount (2)
> > +calls with
> > +.BR MS_BIND .
> > +.P
> > +.in +4n
> > +.EX
> > +int srcfd = open_tree(AT_FDCWD, "/var", OPEN_TREE_CLONE);
> > +move_mount(srcfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> > +.EE
> > +.in
> > +.P
> > +First,
> > +a detached bind-mount mount object of
> > +.I /var
> > +is created
> > +and associated with the file descriptor
> > +.IR srcfd .
> > +Then, the mount object is attached to
> > +.I /mnt
> > +using
> > +.BR move_mount (2)
> > +with
> > +.B \%MOVE_MOUNT_F_EMPTY_PATH
> > +to request that the detached mount object
> > +associated with the file descriptor
> > +.I srcfd
> > +be moved (and thus attached) to
> > +.IR /mnt .
> > +.P
> > +The above procedure is functionally equivalent to
> > +the following mount operation using
> > +.BR mount (2):
> > +.P
> > +.in +4n
> > +.EX
> > +mount("/var", "/mnt", NULL, MS_BIND, NULL);
> > +.EE
> > +.in
> > +.P
> > +.B \%OPEN_TREE_CLONE
> > +can be combined with
> > +.B \%AT_RECURSIVE
> > +to create recursive detached bind-mount mount objects,
> > +which in turn can be attached to mount points
> > +to create recursive bind-mounts.
> > +.P
> > +.in +4n
> > +.EX
> > +int srcfd = open_tree(AT_FDCWD, "/var", OPEN_TREE_CLONE | AT_RECURSIVE);
> > +move_mount(srcfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> > +.EE
> > +.in
> > +.P
> > +The above procedure is functionally equivalent to
> > +the following mount operation using
> > +.BR mount (2):
> > +.P
> > +.in +4n
> > +.EX
> > +mount("/var", "/mnt", NULL, MS_BIND | MS_REC, NULL);
> > +.EE
> > +.in
> > +.P
> > +One of the primary benefits of using
> > +.BR open_tree ()
> > +and
> > +.BR move_mount (2)
> > +over the traditional
> > +.BR mount (2)
> > +is that operating with
> > +.IR dirfd -style
> > +file descriptors is far easier and more intuitive.
> > +.P
> > +.in +4n
> > +.EX
> > +int srcfd = open_tree(100, "", AT_EMPTY_PATH | OPEN_TREE_CLONE);
> > +move_mount(srcfd, "", 200, "foo", MOVE_MOUNT_F_EMPTY_PATH);
> > +.EE
> > +.in
> > +.P
> > +The above procedure is roughly equivalent to
> > +the following mount operation using
> > +.BR mount (2):
> > +.P
> > +.in +4n
> > +.EX
> > +mount("/proc/self/fd/100", "/proc/self/fd/200/foo", NULL, MS_BIND, NULL);
> > +.EE
> > +.in
> > +.P
> > +In addition, you can use the file descriptor returned by
> > +.BR open_tree ()
> > +as the
> > +.I dirfd
> > +argument to any "*at()" system calls:
> > +.P
> > +.in +4n
> > +.EX
> > +int dirfd, fd;
> > +\&
> > +dirfd = open_tree(AT_FDCWD, "/etc", OPEN_TREE_CLONE);
> > +fd = openat(dirfd, "passwd", O_RDONLY);
> > +fchmodat(dirfd, "shadow", 0000, 0);
> > +close(dirfd);
> > +close(fd);
> > +/* The bind-mount is now destroyed. */
> > +.EE
> > +.in
> > +.SH SEE ALSO
> > +.BR fsconfig (2),
> > +.BR fsmount (2),
> > +.BR fsopen (2),
> > +.BR fspick (2),
> > +.BR mount (2),
> > +.BR mount_setattr (2),
> > +.BR move_mount (2),
> > +.BR mount_namespaces (7)
> >
> > --
> > 2.51.0
> >
> >
>
> --
> <https://www.alejandro-colomar.es>
> Use port 80 (that is, <...:80/>).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
* Re: [PATCH v4 05/10] man/man2/fsmount.2: document "new" mount API
From: Askar Safin @ 2025-09-22 1:10 UTC (permalink / raw)
To: safinaskar
Cc: alx, brauner, cyphar, dhowells, g.branden.robinson, jack,
linux-api, linux-fsdevel, linux-kernel, linux-man, mtk.manpages,
safinaskar, viro
In-Reply-To: <20250921230824.92612-1-safinaskar@gmail.com>
> MNT_DETACH, not MOUNT_DETACH
Same for open_tree and open_tree_attr
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v4 10/10] man/man2/{fsconfig,mount_setattr}.2: add note about attribute-parameter distinction
From: Askar Safin @ 2025-09-22 1:06 UTC (permalink / raw)
To: cyphar
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, safinaskar,
viro
In-Reply-To: <20250919-new-mount-api-v4-10-1261201ab562@cyphar.com>
> Some mount attributes (traditionally associated with mount(8)-style options) have a sibling mount attribute with superficially similar user-facing behaviour
"Some mount attributes... have a sibling mount attribute"
Something is wrong here.
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v4 03/10] man/man2/fspick.2: document "new" mount API
From: Askar Safin @ 2025-09-22 0:25 UTC (permalink / raw)
To: cyphar
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, safinaskar,
viro
In-Reply-To: <20250919-new-mount-api-v4-3-1261201ab562@cyphar.com>
> With the notable caveat that in this example, mount(2) will clear all other filesystem parameters (such as MS_NOSUID or MS_NOEXEC); fsconfig(2) will only modify the ro parameter.
MS_NOSUID and MS_NOEXEC are not filesystem parameters. They can be set per-mount, but not
per-filesystem. Here is list of all filesystem-agnostic per-superblock parameters:
https://elixir.bootlin.com/linux/v6.17-rc6/source/fs/namespace.c#L4103
Note that these SB_* constants are equal to corresponding MS_* constants.
As you can see, there is no NOSUID and NOEXEC in that list.
Also, SB_NOSUID does exist:
https://elixir.bootlin.com/linux/v6.17-rc6/source/include/linux/fs.h#L1240
.
So, it seems that "NOSUID superblock" does exist as a concept. But, thanks to
code in path_mount (provided above) user cannot (in filesystem-agnostic way)
make given superblock NOSUID.
So, from user point of view, NOSUID and NOEXEC are not filesystem parameters.
If you need some example of filesystem parameter, I suggest MS_SYNCHRONOUS,
I used it here:
https://lore.kernel.org/all/198d1f2e189.11dbac16b2998.3847935512688537521@zohomail.com/
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v4 05/10] man/man2/fsmount.2: document "new" mount API
From: Askar Safin @ 2025-09-21 23:08 UTC (permalink / raw)
To: cyphar
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, safinaskar,
viro
In-Reply-To: <20250919-new-mount-api-v4-5-1261201ab562@cyphar.com>
> Note that the unmount operation on close(2) is lazy—akin to calling umount2(2) with MOUNT_DETACH
MNT_DETACH, not MOUNT_DETACH
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v3 07/30] kho: add interfaces to unpreserve folios and physical memory ranges
From: Pasha Tatashin @ 2025-09-21 22:20 UTC (permalink / raw)
To: Jason Gunthorpe
Cc: Mike Rapoport, pratyush, jasonmiu, graf, changyuanl, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, zhangguopeng, linux, linux-kernel, linux-doc, linux-mm,
gregkh, tglx, mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, parav, leonro, witu
In-Reply-To: <20250818135509.GK802098@nvidia.com>
On Mon, Aug 18, 2025 at 9:55 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Fri, Aug 15, 2025 at 12:12:10PM +0300, Mike Rapoport wrote:
> > > Which is perhaps another comment, if this __get_free_pages() is going
> > > to be a common pattern (and I guess it will be) then the API should be
> > > streamlined alot more:
> > >
> > > void *kho_alloc_preserved_memory(gfp, size);
> > > void kho_free_preserved_memory(void *);
> >
> > This looks backwards to me. KHO should not deal with memory allocation,
> > it's responsibility to preserve/restore memory objects it supports.
>
> Then maybe those are luo_ helpers
>
> But having users open code __get_free_pages() and convert to/from
> struct page, phys, etc is not a great idea.
I added:
void *luo_contig_alloc_preserve(size_t size);
void luo_contig_free_unpreserve(void *mem, size_t size);
Allocate contiguous, zeroed, and preserved memory.
Pasha
^ permalink raw reply
* Re: [PATCH v4 03/10] man/man2/fspick.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-21 15:17 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-09-21-petite-busy-mucus-rite-01PHer@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 2071 bytes --]
Hi Aleksa,
On Mon, Sep 22, 2025 at 12:55:13AM +1000, Aleksa Sarai wrote:
> > This should use '.B. (Bold). BR means alternating Bold and Roman, but
> > this only has one token, so it can't alternate.
> >
> > If you run `make -R build-catman-troff`, this will trigger a diagnostic:
> >
> > an.tmac: <page>:<line>: style: .BR expects at least 2 arguments, got 1
>
> Grr, I thought I fixed all of these. I must've changed it in a rework
> and forgot to fix it.
No problem; mistakes happen. :)
> > > +Please note that\[em]in contrast to
> > > +the behaviour of
> > > +.B MS_REMOUNT
> > > +with
> > > +.BR mount (2)\[em] fspick ()
> >
> > Only have one important keyword per macro call. In this case, I prefer
> > em dashes to only be attached to one side, as if they were parentheses,
> > so we don't need any tricks:
> >
> > Please note that
> > \[em]in contrast to
> > ...
> > .BR mount (2)\[em]
> > .BR fspick ()
>
> Based on my testing, doing it that way adds whitespace to one side of
> the em dash
You're correct; this adds whitespace on one side of the em dash.
> and typographically em dashes should not have whitespace on
> either side AFAIK.
This rule differs for different style guides, and different languages.
In Spanish, the most common style is having spaces as if the dashes
were parentheses; very much in a logical style, like quotes not having
extraneous punctuation inside them.
I very much prefer the Spanish conventions, and dislike the more common
used conventions for English. I don't know if Branden can illustrate us
with some history about em dashes.
> If there is a way to get the layout right without
> breaking the "one macro per line" rule, I'd love to know! :D
There's a way. I'll show it just for your curiosity. :D
.BR mount (2)\[em]\c
.BR fspick ()
(I hope it works, because I haven't tested it. Accidental typos might
break my untested examples.) :)
Cheers,
Alex
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 03/10] man/man2/fspick.2: document "new" mount API
From: Aleksa Sarai @ 2025-09-21 14:55 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <y77zyujsduf5furdf2biphuszil63kftb44cs74ed2d2hf2gdr@hci7mzt6yh7b>
[-- Attachment #1: Type: text/plain, Size: 11709 bytes --]
On 2025-09-21, Alejandro Colomar <alx@kernel.org> wrote:
> Hi Aleksa,
>
> On Fri, Sep 19, 2025 at 11:59:44AM +1000, Aleksa Sarai wrote:
> > This is loosely based on the original documentation written by David
> > Howells and later maintained by Christian Brauner, but has been
> > rewritten to be more from a user perspective (as well as fixing a few
> > critical mistakes).
> >
> > Co-authored-by: David Howells <dhowells@redhat.com>
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > Co-authored-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> > ---
> > man/man2/fspick.2 | 342 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 342 insertions(+)
> >
> > diff --git a/man/man2/fspick.2 b/man/man2/fspick.2
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..1f87293f44658adeb7ab7cffebcac3174888f040
> > --- /dev/null
> > +++ b/man/man2/fspick.2
> > @@ -0,0 +1,342 @@
> > +.\" Copyright, the authors of the Linux man-pages project
> > +.\"
> > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> > +.\"
> > +.TH fspick 2 (date) "Linux man-pages (unreleased)"
> > +.SH NAME
> > +fspick \- select filesystem for reconfiguration
> > +.SH LIBRARY
> > +Standard C library
> > +.RI ( libc ,\~ \-lc )
> > +.SH SYNOPSIS
> > +.nf
> > +.BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */"
> > +.B #include <sys/mount.h>
> > +.P
> > +.BI "int fspick(int " dirfd ", const char *" path ", unsigned int " flags );
> > +.fi
> > +.SH DESCRIPTION
> > +The
> > +.BR fspick ()
> > +system call is part of
> > +the suite of file descriptor based mount facilities in Linux.
> > +.P
> > +.BR fspick()
> > +creates a new filesystem configuration context
> > +for the extant filesystem instance
> > +associated with the path described by
> > +.IR dirfd
> > +and
> > +.IR path ,
> > +places it into reconfiguration mode
> > +(similar to
> > +.BR mount (8)
> > +with the
> > +.I -o remount
> > +option).
> > +A new file descriptor
> > +associated with the filesystem configuration context
> > +is then returned.
> > +The calling process must have the
> > +.BR CAP_SYS_ADMIN
>
> This should use '.B. (Bold). BR means alternating Bold and Roman, but
> this only has one token, so it can't alternate.
>
> If you run `make -R build-catman-troff`, this will trigger a diagnostic:
>
> an.tmac: <page>:<line>: style: .BR expects at least 2 arguments, got 1
Grr, I thought I fixed all of these. I must've changed it in a rework
and forgot to fix it.
> > +capability in order to create a new filesystem configuration context.
> > +.P
> > +The resultant file descriptor can be used with
> > +.BR fsconfig (2)
> > +to specify the desired set of changes to
> > +filesystem parameters of the filesystem instance.
> > +Once the desired set of changes have been configured,
> > +the changes can be effectuated by calling
> > +.BR fsconfig (2)
> > +with the
> > +.B \%FSCONFIG_CMD_RECONFIGURE
> > +command.
> > +Please note that\[em]in contrast to
> > +the behaviour of
> > +.B MS_REMOUNT
> > +with
> > +.BR mount (2)\[em] fspick ()
>
> Only have one important keyword per macro call. In this case, I prefer
> em dashes to only be attached to one side, as if they were parentheses,
> so we don't need any tricks:
>
> Please note that
> \[em]in contrast to
> ...
> .BR mount (2)\[em]
> .BR fspick ()
Based on my testing, doing it that way adds whitespace to one side of
the em dash and typographically em dashes should not have whitespace on
either side AFAIK. If there is a way to get the layout right without
breaking the "one macro per line" rule, I'd love to know! :D
> > +instantiates the filesystem configuration context
> > +with a copy of
> > +the extant filesystem's filesystem parameters,
> > +meaning that a subsequent
> > +.B \%FSCONFIG_CMD_RECONFIGURE
> > +operation
> > +will only update filesystem parameters
> > +explicitly modified with
> > +.BR fsconfig (2).
> > +.P
> > +As with "*at()" system calls,
> > +.BR fspick ()
> > +uses the
> > +.I dirfd
> > +argument in conjunction with the
> > +.I path
> > +argument to determine the path to operate on, as follows:
> > +.IP \[bu] 3
> > +If the pathname given in
> > +.I path
> > +is absolute, then
> > +.I dirfd
> > +is ignored.
> > +.IP \[bu]
> > +If the pathname given in
> > +.I path
> > +is relative and
> > +.I dirfd
> > +is the special value
> > +.BR \%AT_FDCWD ,
> > +then
> > +.I path
> > +is interpreted relative to
> > +the current working directory
> > +of the calling process (like
> > +.BR open (2)).
> > +.IP \[bu]
> > +If the pathname given in
> > +.I path
> > +is relative,
> > +then it is interpreted relative to
> > +the directory referred to by the file descriptor
> > +.I dirfd
> > +(rather than relative to
> > +the current working directory
> > +of the calling process,
> > +as is done by
> > +.BR open (2)
> > +for a relative pathname).
> > +In this case,
> > +.I dirfd
> > +must be a directory
> > +that was opened for reading
> > +.RB ( O_RDONLY )
> > +or using the
> > +.B O_PATH
> > +flag.
> > +.IP \[bu]
> > +If
> > +.I path
> > +is an empty string,
> > +and
> > +.I flags
> > +contains
> > +.BR \%FSPICK_EMPTY_PATH ,
> > +then the file descriptor
> > +.I dirfd
> > +is operated on directly.
> > +In this case,
> > +.I dirfd
> > +may refer to any type of file,
> > +not just a directory.
> > +.P
> > +See
> > +.BR openat (2)
> > +for an explanation of why the
> > +.I dirfd
> > +argument is useful.
> > +.P
> > +.I flags
> > +can be used to control aspects of how
> > +.I path
> > +is resolved and
> > +properties of the returned file descriptor.
> > +A value for
> > +.I flags
> > +is constructed by bitwise ORing
> > +zero or more of the following constants:
> > +.RS
> > +.TP
> > +.B FSPICK_CLOEXEC
> > +Set the close-on-exec
> > +.RB ( FD_CLOEXEC )
> > +flag on the new file descriptor.
> > +See the description of the
> > +.B O_CLOEXEC
> > +flag in
> > +.BR open (2)
> > +for reasons why this may be useful.
> > +.TP
> > +.B FSPICK_EMPTY_PATH
> > +If
> > +.I path
> > +is an empty string,
> > +operate on the file referred to by
> > +.I dirfd
> > +(which may have been obtained from
> > +.BR open (2),
> > +.BR fsmount (2),
> > +or
> > +.BR open_tree (2)).
> > +In this case,
> > +.I dirfd
> > +may refer to any type of file,
> > +not just a directory.
> > +If
> > +.I dirfd
> > +is
> > +.BR \%AT_FDCWD ,
> > +.BR fspick ()
> > +will operate on the current working directory
> > +of the calling process.
> > +.TP
> > +.B FSPICK_SYMLINK_NOFOLLOW
> > +Do not follow symbolic links
> > +in the terminal component of
> > +.IR path .
> > +If
> > +.I path
> > +references a symbolic link,
> > +the returned filesystem context will reference
> > +the filesystem that the symbolic link itself resides on.
> > +.TP
> > +.B FSPICK_NO_AUTOMOUNT
> > +Do not automount any automount points encountered
> > +while resolving
> > +.IR path .
> > +This allows you to reconfigure an automount point,
> > +rather than the location that would be mounted.
> > +This flag has no effect if
> > +the automount point has already been mounted over.
>
> I'll amend other similar issues if I find them, but in general, I'd put
> the 'if' in the next line, as it is more tied to that part of the
> sentence (think for example that if you reversed the sentence to say
> "if ..., then ...", you'd move the 'if' with what follows it. You don't
> need to search for all of these and fix them; just keep it in mind for
> next time. In general I like the break points you used.
>
>
> Have a lovely day!
> Alex
>
> > +.RE
> > +.P
> > +As with filesystem contexts created with
> > +.BR fsopen (2),
> > +the file descriptor returned by
> > +.BR fspick ()
> > +may be queried for message strings at any time by calling
> > +.BR read (2)
> > +on the file descriptor.
> > +(See the "Message retrieval interface" subsection in
> > +.BR fsopen (2)
> > +for more details on the message format.)
> > +.SH RETURN VALUE
> > +On success, a new file descriptor is returned.
> > +On error, \-1 is returned, and
> > +.I errno
> > +is set to indicate the error.
> > +.SH ERRORS
> > +.TP
> > +.B EACCES
> > +Search permission is denied
> > +for one of the directories
> > +in the path prefix of
> > +.IR path .
> > +(See also
> > +.BR path_resolution (7).)
> > +.TP
> > +.B EBADF
> > +.I path
> > +is relative but
> > +.I dirfd
> > +is neither
> > +.B \%AT_FDCWD
> > +nor a valid file descriptor.
> > +.TP
> > +.B EFAULT
> > +.I path
> > +is NULL
> > +or a pointer to a location
> > +outside the calling process's accessible address space.
> > +.TP
> > +.B EINVAL
> > +Invalid flag specified in
> > +.IR flags .
> > +.TP
> > +.B ELOOP
> > +Too many symbolic links encountered when resolving
> > +.IR path .
> > +.TP
> > +.B EMFILE
> > +The calling process has too many open files to create more.
> > +.TP
> > +.B ENAMETOOLONG
> > +.I path
> > +is longer than
> > +.BR PATH_MAX .
> > +.TP
> > +.B ENFILE
> > +The system has too many open files to create more.
> > +.TP
> > +.B ENOENT
> > +A component of
> > +.I path
> > +does not exist,
> > +or is a dangling symbolic link.
> > +.TP
> > +.B ENOENT
> > +.I path
> > +is an empty string, but
> > +.B \%FSPICK_EMPTY_PATH
> > +is not specified in
> > +.IR flags .
> > +.TP
> > +.B ENOTDIR
> > +A component of the path prefix of
> > +.I path
> > +is not a directory;
> > +or
> > +.I path
> > +is relative and
> > +.I dirfd
> > +is a file descriptor referring to a file other than a directory.
> > +.TP
> > +.B ENOMEM
> > +The kernel could not allocate sufficient memory to complete the operation.
> > +.TP
> > +.B EPERM
> > +The calling process does not have the required
> > +.B \%CAP_SYS_ADMIN
> > +capability.
> > +.SH STANDARDS
> > +Linux.
> > +.SH HISTORY
> > +Linux 5.2.
> > +.\" commit cf3cba4a429be43e5527a3f78859b1bfd9ebc5fb
> > +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> > +glibc 2.36.
> > +.SH EXAMPLES
> > +The following example sets the read-only flag
> > +on the filesystem instance referenced by
> > +the mount object attached at
> > +.IR /tmp .
> > +.P
> > +.in +4n
> > +.EX
> > +int fsfd = fspick(AT_FDCWD, "/tmp", FSPICK_CLOEXEC);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0);
> > +.EE
> > +.in
> > +.P
> > +The above procedure is roughly equivalent to
> > +the following mount operation using
> > +.BR mount (2):
> > +.P
> > +.in +4n
> > +.EX
> > +mount(NULL, "/tmp", NULL, MS_REMOUNT | MS_RDONLY, NULL);
> > +.EE
> > +.in
> > +.P
> > +With the notable caveat that
> > +in this example,
> > +.BR mount (2)
> > +will clear all other filesystem parameters
> > +(such as
> > +.B MS_NOSUID
> > +or
> > +.BR MS_NOEXEC );
> > +.BR fsconfig (2)
> > +will only modify the
> > +.I ro
> > +parameter.
> > +.SH SEE ALSO
> > +.BR fsconfig (2),
> > +.BR fsmount (2),
> > +.BR fsopen (2),
> > +.BR mount (2),
> > +.BR mount_setattr (2),
> > +.BR move_mount (2),
> > +.BR open_tree (2),
> > +.BR mount_namespaces (7)
> > +
> >
> > --
> > 2.51.0
> >
>
> --
> <https://www.alejandro-colomar.es>
> Use port 80 (that is, <...:80/>).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
* Re: [PATCH v4 08/10] man/man2/mount_setattr.2: mirror opening sentence from fsopen(2)
From: Alejandro Colomar @ 2025-09-21 10:19 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-09-21-sad-swampy-pillar-rigor-ESCPmx@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 2175 bytes --]
On Sun, Sep 21, 2025 at 08:03:08PM +1000, Aleksa Sarai wrote:
> On 2025-09-21, Alejandro Colomar <alx@kernel.org> wrote:
> > Hi Aleksa,
> >
> > On Fri, Sep 19, 2025 at 11:59:49AM +1000, Aleksa Sarai wrote:
> > > All of the other new mount API docs have this lead-in sentence in order
> > > to make this set of APIs feel a little bit more cohesive. Despite being
> > > a bit of a latecomer, mount_setattr(2) is definitely part of this family
> > > of APIs and so deserves the same treatment.
> > >
> > > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> >
> > Thanks! I've applied this patch.
> > <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=7022531182883ed1db5d4c926506cd373e0795ee>
> > (Use port :80/)
>
> Ah, you forgot to switch to "file-descriptor-based" like you suggested
> in patch 1. ;)
Oh, thanks for the reminder! :-)
I've amended it, and now pushed to <kernel.org>.
Cheers,
Alex
>
> >
> > Cheers,
> > Alex
> >
> > > ---
> > > man/man2/mount_setattr.2 | 6 +++++-
> > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
> > > index 4b55f6d2e09d00d9bc4b3a085f310b1b459f34e8..b27db5b96665cfb0c387bf5b60776d45e0139956 100644
> > > --- a/man/man2/mount_setattr.2
> > > +++ b/man/man2/mount_setattr.2
> > > @@ -19,7 +19,11 @@ .SH SYNOPSIS
> > > .SH DESCRIPTION
> > > The
> > > .BR mount_setattr ()
> > > -system call changes the mount properties of a mount or an entire mount tree.
> > > +system call is part of
> > > +the suite of file descriptor based mount facilities in Linux.
> > > +.P
> > > +.BR mount_setattr ()
> > > +changes the mount properties of a mount or an entire mount tree.
> > > If
> > > .I path
> > > is relative,
> > >
> > > --
> > > 2.51.0
> > >
> >
> > --
> > <https://www.alejandro-colomar.es>
> > Use port 80 (that is, <...:80/>).
>
>
>
> --
> Aleksa Sarai
> Senior Software Engineer (Containers)
> SUSE Linux GmbH
> https://www.cyphar.com/
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 08/10] man/man2/mount_setattr.2: mirror opening sentence from fsopen(2)
From: Aleksa Sarai @ 2025-09-21 10:03 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <fqgxjzw5dxsd6ymm4tmvxmokq4uh2xo6lk5rqhjg4tjw5eblgg@wy5kbuhwmfnx>
[-- Attachment #1: Type: text/plain, Size: 1802 bytes --]
On 2025-09-21, Alejandro Colomar <alx@kernel.org> wrote:
> Hi Aleksa,
>
> On Fri, Sep 19, 2025 at 11:59:49AM +1000, Aleksa Sarai wrote:
> > All of the other new mount API docs have this lead-in sentence in order
> > to make this set of APIs feel a little bit more cohesive. Despite being
> > a bit of a latecomer, mount_setattr(2) is definitely part of this family
> > of APIs and so deserves the same treatment.
> >
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
>
> Thanks! I've applied this patch.
> <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=7022531182883ed1db5d4c926506cd373e0795ee>
> (Use port :80/)
Ah, you forgot to switch to "file-descriptor-based" like you suggested
in patch 1. ;)
>
> Cheers,
> Alex
>
> > ---
> > man/man2/mount_setattr.2 | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
> > index 4b55f6d2e09d00d9bc4b3a085f310b1b459f34e8..b27db5b96665cfb0c387bf5b60776d45e0139956 100644
> > --- a/man/man2/mount_setattr.2
> > +++ b/man/man2/mount_setattr.2
> > @@ -19,7 +19,11 @@ .SH SYNOPSIS
> > .SH DESCRIPTION
> > The
> > .BR mount_setattr ()
> > -system call changes the mount properties of a mount or an entire mount tree.
> > +system call is part of
> > +the suite of file descriptor based mount facilities in Linux.
> > +.P
> > +.BR mount_setattr ()
> > +changes the mount properties of a mount or an entire mount tree.
> > If
> > .I path
> > is relative,
> >
> > --
> > 2.51.0
> >
>
> --
> <https://www.alejandro-colomar.es>
> Use port 80 (that is, <...:80/>).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
* Re: [PATCH v4 10/10] man/man2/{fsconfig,mount_setattr}.2: add note about attribute-parameter distinction
From: Alejandro Colomar @ 2025-09-21 9:59 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-10-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 3498 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:51AM +1000, Aleksa Sarai wrote:
> This was not particularly well documented in mount(8) nor mount(2), and
> since this is a fairly notable aspect of the new mount API, we should
> probably add some words about it.
>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
> man/man2/fsconfig.2 | 12 ++++++++++++
> man/man2/mount_setattr.2 | 40 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 52 insertions(+)
>
> diff --git a/man/man2/fsconfig.2 b/man/man2/fsconfig.2
> index 5a18e08c700ac93aa22c341b4134944ee3c38d0b..d827a7b96e08284fb025f94c3348a4acc4571b7d 100644
> --- a/man/man2/fsconfig.2
> +++ b/man/man2/fsconfig.2
> @@ -579,6 +579,18 @@ .SS Generic filesystem parameters
> Linux Security Modules (LSMs)
> are also generic with respect to the underlying filesystem.
> See the documentation for the LSM you wish to configure for more details.
> +.SS Mount attributes and filesystem parameters
> +Some filesystem parameters
> +(traditionally associated with
> +.BR mount (8)-style
> +options)
> +have a sibling mount attribute
> +with superficially similar user-facing behaviour.
> +.P
> +For a description of the distinction between
> +mount attributes and filesystem parameters,
> +see the "Mount attributes and filesystem parameters" subsection of
> +.BR mount_setattr (2).
> .SH CAVEATS
> .SS Filesystem parameter types
> As a result of
> diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
> index b27db5b96665cfb0c387bf5b60776d45e0139956..f7d0b96fddf97698e36cab020f1d695783143025 100644
> --- a/man/man2/mount_setattr.2
> +++ b/man/man2/mount_setattr.2
> @@ -790,6 +790,46 @@ .SS ID-mapped mounts
> .BR chown (2)
> system call changes the ownership globally and permanently.
> .\"
> +.SS Mount attributes and filesystem parameters
> +Some mount attributes
> +(traditionally associated with
> +.BR mount (8)-style
> +options)
> +have a sibling mount attribute
> +with superficially similar user-facing behaviour.
> +For example, the
> +.I -o ro
As said in another page, this should be
.I \-o\~ro
> +option to
> +.BR mount (8)
> +can refer to the
> +"read-only" filesystem parameter,
> +or the "read-only" mount attribute.
> +Both of these result in mount objects becoming read-only,
> +but they do have different behaviour.
> +.P
> +The distinction between these two kinds of option is that
> +mount object attributes are applied per-mount-object
> +(allowing different mount objects
> +derived from a given filesystem instance
> +to have different attributes),
> +while filesystem instance parameters
> +("superblock flags" in kernel-developer parlance)
> +apply to all mount objects
> +derived from the same filesystem instance.
> +.P
> +When using
> +.BR mount (2),
> +the line between these two types of mount options was blurred.
> +However, with
> +.BR mount_setattr ()
> +and
> +.BR fsconfig (2),
> +the distinction is made much clearer.
> +Mount attributes are configured with
> +.BR mount_setattr (),
> +while filesystem parameters can be configured using
> +.BR fsconfig (2).
> +.\"
LGTM.
I've finished with the review of the patch set. It's quite good. :)
Have a lovely day!
Alex
> .SS Extensibility
> In order to allow for future extensibility,
> .BR mount_setattr ()
>
> --
> 2.51.0
>
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 00/10] man2: document "new" mount API
From: Aleksa Sarai @ 2025-09-21 9:58 UTC (permalink / raw)
To: Askar Safin
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, safinaskar,
viro
In-Reply-To: <20250921024310.80511-1-safinaskar@gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1821 bytes --]
On 2025-09-21, Askar Safin <safinaskar@gmail.com> wrote:
> Aleksa, thank you! Don't give up. We all need these manpages.
>
> I see you didn't address some my previous notes.
>
> * move_mount(2) still says "Mount objects cannot be attached beneath the filesystem root".
> I suggest saying "root directory" or "root" or "root directory of the process" or just "/"
> instead. But you may keep this phrase as is, of course.
>
> * Docs for FSPICK_NO_AUTOMOUNT in fspick(2) are still wrong. They say that FSPICK_NO_AUTOMOUNT
> affects all components of path. Similar thing applies to mount_setattr(2) and move_mount(2)
Sorry, I last read through your review comments a month ago, I must've
forgotten to make these changes back then. I'll include them in v5.
(It seems I remembered to change the open_tree(2) automount one but
forgot to do it for the others, oops!)
> * open_tree(2) still says:
> > If flags does not contain OPEN_TREE_CLONE, open_tree() returns a file descriptor
> > that is exactly equivalent to one produced by openat(2) when called with the same dirfd and path.
>
> This is not true if automounts are involved. I suggest adding "modulo automounts". But you may
> keep everything, of course.
Hmmm. As we discussed last time, this sentence is more intended to
indicate that the file descriptor is just a regular open file (with no
dissolve_on_fput() + FMODE_NEED_UNMOUNT magic) rather than the exact
behaviour you get with regards to path lookup.
I would honestly prefer to remove "when called with the same dirfd and
path" rather than add caveats, but I think it makes the sentence less
readable... I'll think about it and try to fix this wording up somehow
for v5.
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
* Re: [PATCH v4 09/10] man/man2/open_tree{,_attr}.2: document new open_tree_attr() API
From: Alejandro Colomar @ 2025-09-21 9:55 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-9-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 6625 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:50AM +1000, Aleksa Sarai wrote:
> This is a new API added in Linux 6.15, and is effectively just a minor
> expansion of open_tree(2) in order to allow for MOUNT_ATTR_IDMAP to be
> changed for an existing ID-mapped mount. glibc does not yet have a
> wrapper for this.
>
> While working on this man-page, I discovered a bug in open_tree_attr(2)
> that accidentally permitted changing MOUNT_ATTR_IDMAP for extant
> detached ID-mapped mount objects. This is definitely a bug, but there
> is no need to add this to BUGS because the patch to fix this has already
> been accepted (slated for 6.18, and will be backported to 6.15+).
Okay.
>
> Cc: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
> man/man2/open_tree.2 | 140 ++++++++++++++++++++++++++++++++++++++++++++++
> man/man2/open_tree_attr.2 | 1 +
> 2 files changed, 141 insertions(+)
>
> diff --git a/man/man2/open_tree.2 b/man/man2/open_tree.2
> index 7f85df08b43c7b48a9d021dbbeb2c60092a2b2d4..60de4313a9d5be4ef3ff1217051f252506a2ade9 100644
> --- a/man/man2/open_tree.2
> +++ b/man/man2/open_tree.2
> @@ -15,7 +15,19 @@ .SH SYNOPSIS
> .B #include <sys/mount.h>
> .P
> .BI "int open_tree(int " dirfd ", const char *" path ", unsigned int " flags );
> +.P
> +.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
> +.P
> +.BI "int syscall(SYS_open_tree_attr, int " dirfd ", const char *" path ,
> +.BI " unsigned int " flags ", struct mount_attr *_Nullable " attr ", \
> +size_t " size );
Do we maybe want to move this to its own separate page?
The separate page could perfectly contain the same exact text you're
adding here; you don't need to repeat open_tree() descriptions.
In general, I feel that while this improves discoverability of related
functions, it produces more complex pages.
Cheers,
Alex
> .fi
> +.P
> +.IR Note :
> +glibc provides no wrapper for
> +.BR open_tree_attr (),
> +necessitating the use of
> +.BR syscall (2).
> .SH DESCRIPTION
> The
> .BR open_tree ()
> @@ -246,6 +258,129 @@ .SH DESCRIPTION
> as a detached mount object.
> This flag is only permitted in conjunction with
> .BR \%OPEN_TREE_CLONE .
> +.SS open_tree_attr()
> +The
> +.BR open_tree_attr ()
> +system call operates in exactly the same way as
> +.BR open_tree (),
> +except for the differences described here.
> +.P
> +After performing the same operation as with
> +.BR open_tree (),
> +.BR open_tree_attr ()
> +will apply the mount attribute changes described in
> +.I attr
> +to the file descriptor before it is returned.
> +(See
> +.BR mount_attr (2type)
> +for a description of the
> +.I mount_attr
> +structure.
> +As described in
> +.BR mount_setattr (2),
> +.I size
> +must be set to
> +.I sizeof(struct mount_attr)
> +in order to support future extensions.)
> +If
> +.I attr
> +is NULL,
> +or has
> +.IR attr.attr_clr ,
> +.IR attr.attr_set ,
> +and
> +.I attr.propagation
> +all set to zero,
> +then
> +.BR open_tree_attr ()
> +has identical behaviour to
> +.BR open_tree ().
> +.P
> +The application of
> +.I attr
> +to the resultant file descriptor
> +has identical semantics to
> +.BR mount_setattr (2),
> +except for the following extensions and general caveats:
> +.IP \[bu] 3
> +Unlike
> +.BR mount_setattr (2)
> +called with a regular
> +.B OPEN_TREE_CLONE
> +detached mount object from
> +.BR open_tree (),
> +.BR open_tree_attr ()
> +can specify a different setting for
> +.B \%MOUNT_ATTR_IDMAP
> +to the original mount object cloned with
> +.BR OPEN_TREE_CLONE .
> +.IP
> +Adding
> +.B \%MOUNT_ATTR_IDMAP
> +to
> +.I attr.attr_clr
> +will disable ID-mapping for the new mount object;
> +adding
> +.B \%MOUNT_ATTR_IDMAP
> +to
> +.I attr.attr_set
> +will configure the mount object to have the ID-mapping defined by
> +the user namespace referenced by the file descriptor
> +.IR attr.userns_fd .
> +(The semantics of which are identical to when
> +.BR mount_setattr (2)
> +is used to configure
> +.BR \%MOUNT_ATTR_IDMAP .)
> +.IP
> +Changing or removing the mapping
> +of an ID-mapped mount is only permitted
> +if a new detached mount object is being created with
> +.I flags
> +including
> +.BR \%OPEN_TREE_CLONE .
> +.\" Aleksa Sarai
> +.\" At time of writing, this is not actually true because of a bug where
> +.\" open_tree_attr() would accidentally permit changing MOUNT_ATTR_IDMAP for
> +.\" existing detached mount objects without setting OPEN_TREE_CLONE, but a
> +.\" patch to fix it has been slated for 6.18 and will be backported to 6.15+.
> +.\" <https://lore.kernel.org/r/20250808-open_tree_attr-bugfix-idmap-v1-0-0ec7bc05646c@cyphar.com/>
> +.IP \[bu]
> +If
> +.I flags
> +contains
> +.BR \%AT_RECURSIVE ,
> +then the attributes described in
> +.I attr
> +are applied recursively
> +(just as when
> +.BR mount_setattr (2)
> +is called with
> +.BR \%AT_RECURSIVE ).
> +However, this applies in addition to the
> +.BR open_tree ()-specific
> +behaviour regarding
> +.BR \%AT_RECURSIVE ,
> +and thus
> +.I flags
> +must also contain
> +.BR \%OPEN_TREE_CLONE .
> +.P
> +Note that if
> +.I flags
> +does not contain
> +.BR \%OPEN_TREE_CLONE ,
> +.BR open_tree_attr ()
> +will attempt to modify the mount attributes of
> +the mount object attached at
> +the path described by
> +.I dirfd
> +and
> +.IR path .
> +As with
> +.BR mount_setattr (2),
> +if said path is not a mount point,
> +.BR open_tree_attr ()
> +will return an error.
> .SH RETURN VALUE
> On success, a new file descriptor is returned.
> On error, \-1 is returned, and
> @@ -339,10 +474,15 @@ .SH ERRORS
> .SH STANDARDS
> Linux.
> .SH HISTORY
> +.SS open_tree()
> Linux 5.2.
> .\" commit a07b20004793d8926f78d63eb5980559f7813404
> .\" commit 400913252d09f9cfb8cce33daee43167921fc343
> glibc 2.36.
> +.SS open_tree_attr()
> +Linux 6.15.
> +.\" commit c4a16820d90199409c9bf01c4f794e1e9e8d8fd8
> +.\" commit 7a54947e727b6df840780a66c970395ed9734ebe
> .SH NOTES
> .SS Mount propagation
> The bind-mount mount objects created by
> diff --git a/man/man2/open_tree_attr.2 b/man/man2/open_tree_attr.2
> new file mode 100644
> index 0000000000000000000000000000000000000000..e57269bbd269bcce0b0a974425644ba75e379f2f
> --- /dev/null
> +++ b/man/man2/open_tree_attr.2
> @@ -0,0 +1 @@
> +.so man2/open_tree.2
>
> --
> 2.51.0
>
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 08/10] man/man2/mount_setattr.2: mirror opening sentence from fsopen(2)
From: Alejandro Colomar @ 2025-09-21 9:50 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-8-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 1456 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:49AM +1000, Aleksa Sarai wrote:
> All of the other new mount API docs have this lead-in sentence in order
> to make this set of APIs feel a little bit more cohesive. Despite being
> a bit of a latecomer, mount_setattr(2) is definitely part of this family
> of APIs and so deserves the same treatment.
>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Thanks! I've applied this patch.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=7022531182883ed1db5d4c926506cd373e0795ee>
(Use port :80/)
Cheers,
Alex
> ---
> man/man2/mount_setattr.2 | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/man/man2/mount_setattr.2 b/man/man2/mount_setattr.2
> index 4b55f6d2e09d00d9bc4b3a085f310b1b459f34e8..b27db5b96665cfb0c387bf5b60776d45e0139956 100644
> --- a/man/man2/mount_setattr.2
> +++ b/man/man2/mount_setattr.2
> @@ -19,7 +19,11 @@ .SH SYNOPSIS
> .SH DESCRIPTION
> The
> .BR mount_setattr ()
> -system call changes the mount properties of a mount or an entire mount tree.
> +system call is part of
> +the suite of file descriptor based mount facilities in Linux.
> +.P
> +.BR mount_setattr ()
> +changes the mount properties of a mount or an entire mount tree.
> If
> .I path
> is relative,
>
> --
> 2.51.0
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 07/10] man/man2/open_tree.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-21 9:47 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-7-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 15113 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:48AM +1000, Aleksa Sarai wrote:
> This is loosely based on the original documentation written by David
> Howells and later maintained by Christian Brauner, but has been
> rewritten to be more from a user perspective (as well as fixing a few
> critical mistakes).
>
> Co-authored-by: David Howells <dhowells@redhat.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Co-authored-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
> man/man2/open_tree.2 | 498 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 498 insertions(+)
>
> diff --git a/man/man2/open_tree.2 b/man/man2/open_tree.2
> new file mode 100644
> index 0000000000000000000000000000000000000000..7f85df08b43c7b48a9d021dbbeb2c60092a2b2d4
> --- /dev/null
> +++ b/man/man2/open_tree.2
> @@ -0,0 +1,498 @@
> +.\" Copyright, the authors of the Linux man-pages project
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH open_tree 2 (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +open_tree \- open path or create detached mount object and attach to fd
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ,\~ \-lc )
> +.SH SYNOPSIS
> +.nf
> +.BR "#define _GNU_SOURCE " "/* See feature_test_macros(7) */"
> +.BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */"
> +.B #include <sys/mount.h>
> +.P
> +.BI "int open_tree(int " dirfd ", const char *" path ", unsigned int " flags );
> +.fi
> +.SH DESCRIPTION
> +The
> +.BR open_tree ()
> +system call is part of
> +the suite of file descriptor based mount facilities in Linux.
> +.IP \[bu] 3
> +If
> +.I flags
> +contains
> +.BR \%OPEN_TREE_CLONE ,
> +.BR open_tree ()
> +creates a detached mount object
> +which consists of a bind-mount of
> +the path specified by the
> +.IR path .
> +A new file descriptor
> +associated with the detached mount object
> +is then returned.
> +The mount object is equivalent to a bind-mount
> +that would be created by
> +.BR mount (2)
> +called with
> +.BR MS_BIND ,
> +except that it is tied to a file descriptor
> +and is not mounted onto the filesystem.
> +.IP
> +As with file descriptors returned from
> +.BR fsmount (2),
> +the resultant file descriptor can then be used with
> +.BR move_mount (2),
> +.BR mount_setattr (2),
> +or other such system calls to do further mount operations.
> +This mount object will be unmounted and destroyed
> +when the file descriptor is closed
> +if it was not otherwise attached to a mount point
> +by calling
> +.BR move_mount (2).
> +(Note that the unmount operation on
Maybe I would make this note a paragraph of its own; this would give it
more visibility, I think. And I'd remove 'Note that', and start
directly with the noted contents (everything in a manual page must be
noteworthy, in general).
> +.BR close (2)
I'm a bit confused by the reference to close(2). The previous text
mentions closing, but not close(2), so I'm not sure if this refers to
that or if it is comparing it to close(2). Would you mind having a look
at the wording of this entire paragraph?
> +is lazy\[em]akin to calling
I prefer em dashes in both sides of the parenthetical; it more clearly
denotes where it ends.
is lazy
\[em]akin to calling
.BR umount2 (2)
with
.BR MOUNT_DETACH \[em];
(I assume that's where it ends.)
> +.BR umount2 (2)
> +with
> +.BR MOUNT_DETACH ;
> +any existing open references to files
> +from the mount object
> +will continue to work,
> +and the mount object will only be completely destroyed
> +once it ceases to be busy.)
> +.IP \[bu]
> +If
> +.I flags
> +does not contain
> +.BR \%OPEN_TREE_CLONE ,
> +.BR open_tree ()
> +returns a file descriptor
> +that is exactly equivalent to
> +one produced by
> +.BR openat (2)
> +when called with the same
> +.I dirfd
> +and
> +.IR path .
> +.P
> +In either case, the resultant file descriptor
> +acts the same as one produced by
> +.BR open (2)
> +with
> +.BR O_PATH ,
> +meaning it can also be used as a
> +.I dirfd
> +argument to
> +"*at()" system calls.
> +.P
> +As with "*at()" system calls,
> +.BR open_tree ()
> +uses the
> +.I dirfd
> +argument in conjunction with the
> +.I path
> +argument to determine the path to operate on, as follows:
> +.IP \[bu] 3
> +If the pathname given in
> +.I path
> +is absolute, then
> +.I dirfd
> +is ignored.
> +.IP \[bu]
> +If the pathname given in
> +.I path
> +is relative and
> +.I dirfd
> +is the special value
> +.BR \%AT_FDCWD ,
> +then
> +.I path
> +is interpreted relative to
> +the current working directory
> +of the calling process (like
> +.BR open (2)).
> +.IP \[bu]
> +If the pathname given in
> +.I path
> +is relative,
> +then it is interpreted relative to
> +the directory referred to by the file descriptor
> +.I dirfd
> +(rather than relative to
> +the current working directory
> +of the calling process,
> +as is done by
> +.BR open (2)
> +for a relative pathname).
> +In this case,
> +.I dirfd
> +must be a directory
> +that was opened for reading
> +.RB ( O_RDONLY )
> +or using the
> +.B O_PATH
> +flag.
> +.IP \[bu]
> +If
> +.I path
> +is an empty string,
> +and
> +.I flags
> +contains
> +.BR \%AT_EMPTY_PATH ,
> +then the file descriptor
> +.I dirfd
> +is operated on directly.
> +In this case,
> +.I dirfd
> +may refer to any type of file,
> +not just a directory.
> +.P
> +See
> +.BR openat (2)
> +for an explanation of why the
> +.I dirfd
> +argument is useful.
> +.P
> +.I flags
> +can be used to control aspects of the path lookup
> +and properties of the returned file descriptor.
> +A value for
> +.I flags
> +is constructed by bitwise ORing
> +zero or more of the following constants:
> +.RS
> +.TP
> +.B \%AT_EMPTY_PATH
> +If
> +.I path
> +is an empty string, operate on the file referred to by
> +.I dirfd
> +(which may have been obtained from
> +.BR open (2),
> +.BR fsmount(2),
> +or from another
> +.BR open_tree ()
> +call).
> +In this case,
> +.I dirfd
> +may refer to any type of file, not just a directory.
> +If
> +.I dirfd
> +is
> +.BR \%AT_FDCWD ,
> +.BR open_tree ()
> +will operate on the current working directory
> +of the calling process.
> +This flag is Linux-specific; define
> +.B \%_GNU_SOURCE
> +to obtain its definition.
> +.TP
> +.B \%AT_NO_AUTOMOUNT
> +Do not automount the terminal ("basename") component of
> +.I path
> +if it is a directory that is an automount point.
> +This allows you to create a handle to the automount point itself,
> +rather than the location it would mount.
> +This flag has no effect if the mount point has already been mounted over.
> +This flag is Linux-specific; define
> +.B \%_GNU_SOURCE
> +to obtain its definition.
> +.TP
> +.B \%AT_SYMLINK_NOFOLLOW
> +If
> +.I path
> +is a symbolic link, do not dereference it; instead,
> +create either a handle to the link itself
> +or a bind-mount of it.
> +The resultant file descriptor is indistinguishable from one produced by
> +.BR openat (2)
> +with
> +.BR \%O_PATH | O_NOFOLLLOW .
> +.TP
> +.B \%OPEN_TREE_CLOEXEC
> +Set the close-on-exec
> +.RB ( FD_CLOEXEC )
> +flag on the new file descriptor.
> +See the description of the
> +.B O_CLOEXEC
> +flag in
> +.BR open (2)
> +for reasons why this may be useful.
> +.TP
> +.B \%OPEN_TREE_CLONE
> +Rather than creating an
> +.BR openat (2)-style
> +.B O_PATH
> +file descriptor,
> +create a bind-mount of
> +.I path
> +(akin to
> +.IR "mount --bind" )
You need to escape dashes in manual pages. Otherwise, they're formatted
as hyphens, which can't be pasted into the terminal (and another
consequence is not being able to search for them in the man(1) reader
with literal dashes).
Depending on your system, you might be able to search for them or paste
them to the terminal, because some distros patch this in
/etc/local/an.tmac, at the expense of generating lower quality pages,
but in general don't rely on that.
I've noticed now, but this probably also happens in previous pages in
this patch set.
While at it, you should also use a non-breaking space, to keep the
entire command in the same line.
.IR \%mount\~\-\-bind )
Cheers,
Alex
> +as a detached mount object.
> +In order to do this operation,
> +the calling process must have the
> +.BR \%CAP_SYS_ADMIN
> +capability.
> +.TP
> +.B \%AT_RECURSIVE
> +Create a recursive bind-mount of the path
> +(akin to
> +.IR "mount --rbind" )
> +as a detached mount object.
> +This flag is only permitted in conjunction with
> +.BR \%OPEN_TREE_CLONE .
> +.SH RETURN VALUE
> +On success, a new file descriptor is returned.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Search permission is denied for one of the directories
> +in the path prefix of
> +.IR path .
> +(See also
> +.BR path_resolution (7).)
> +.TP
> +.B EBADF
> +.I path
> +is relative but
> +.I dirfd
> +is neither
> +.B \%AT_FDCWD
> +nor a valid file descriptor.
> +.TP
> +.B EFAULT
> +.I path
> +is NULL
> +or a pointer to a location
> +outside the calling process's accessible address space.
> +.TP
> +.B EINVAL
> +Invalid flag specified in
> +.IR flags .
> +.TP
> +.B ELOOP
> +Too many symbolic links encountered when resolving
> +.IR path .
> +.TP
> +.B EMFILE
> +The calling process has too many open files to create more.
> +.TP
> +.B ENAMETOOLONG
> +.I path
> +is longer than
> +.BR PATH_MAX .
> +.TP
> +.B ENFILE
> +The system has too many open files to create more.
> +.TP
> +.B ENOENT
> +A component of
> +.I path
> +does not exist, or is a dangling symbolic link.
> +.TP
> +.B ENOENT
> +.I path
> +is an empty string, but
> +.B AT_EMPTY_PATH
> +is not specified in
> +.IR flags .
> +.TP
> +.B ENOTDIR
> +A component of the path prefix of
> +.I path
> +is not a directory, or
> +.I path
> +is relative and
> +.I dirfd
> +is a file descriptor referring to a file other than a directory.
> +.TP
> +.B ENOSPC
> +The "anonymous" mount namespace
> +necessary to contain the
> +.B \%OPEN_TREE_CLONE
> +detached bind-mount mount object
> +could not be allocated,
> +as doing so would exceed
> +the configured per-user limit on
> +the number of mount namespaces in the current user namespace.
> +(See also
> +.BR namespaces (7).)
> +.TP
> +.B ENOMEM
> +The kernel could not allocate sufficient memory to complete the operation.
> +.TP
> +.B EPERM
> +.I flags
> +contains
> +.B \%OPEN_TREE_CLONE
> +but the calling process does not have the required
> +.B CAP_SYS_ADMIN
> +capability.
> +.SH STANDARDS
> +Linux.
> +.SH HISTORY
> +Linux 5.2.
> +.\" commit a07b20004793d8926f78d63eb5980559f7813404
> +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> +glibc 2.36.
> +.SH NOTES
> +.SS Mount propagation
> +The bind-mount mount objects created by
> +.BR open_tree ()
> +with
> +.B \%OPEN_TREE_CLONE
> +are not associated with
> +the mount namespace of the calling process.
> +Instead, each mount object is placed
> +in a newly allocated "anonymous" mount namespace
> +associated with the calling process.
> +.P
> +One of the side-effects of this is that
> +(unlike bind-mounts created with
> +.BR mount (2)),
> +mount propagation
> +(as described in
> +.BR mount_namespaces (7))
> +will not be applied to bind-mounts created by
> +.BR open_tree ()
> +until the bind-mount is attached with
> +.BR move_mount (2),
> +at which point the mount object
> +will be associated with the mount namespace
> +where it was attached
> +and mount propagation will resume.
> +Note that any mount propagation events that occurred
> +before the mount object was attached
> +will
> +.I not
> +be propagated to the mount object,
> +even after it is attached.
> +.SH EXAMPLES
> +The following examples show how
> +.BR open_tree ()
> +can be used in place of more traditional
> +.BR mount (2)
> +calls with
> +.BR MS_BIND .
> +.P
> +.in +4n
> +.EX
> +int srcfd = open_tree(AT_FDCWD, "/var", OPEN_TREE_CLONE);
> +move_mount(srcfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> +.EE
> +.in
> +.P
> +First,
> +a detached bind-mount mount object of
> +.I /var
> +is created
> +and associated with the file descriptor
> +.IR srcfd .
> +Then, the mount object is attached to
> +.I /mnt
> +using
> +.BR move_mount (2)
> +with
> +.B \%MOVE_MOUNT_F_EMPTY_PATH
> +to request that the detached mount object
> +associated with the file descriptor
> +.I srcfd
> +be moved (and thus attached) to
> +.IR /mnt .
> +.P
> +The above procedure is functionally equivalent to
> +the following mount operation using
> +.BR mount (2):
> +.P
> +.in +4n
> +.EX
> +mount("/var", "/mnt", NULL, MS_BIND, NULL);
> +.EE
> +.in
> +.P
> +.B \%OPEN_TREE_CLONE
> +can be combined with
> +.B \%AT_RECURSIVE
> +to create recursive detached bind-mount mount objects,
> +which in turn can be attached to mount points
> +to create recursive bind-mounts.
> +.P
> +.in +4n
> +.EX
> +int srcfd = open_tree(AT_FDCWD, "/var", OPEN_TREE_CLONE | AT_RECURSIVE);
> +move_mount(srcfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> +.EE
> +.in
> +.P
> +The above procedure is functionally equivalent to
> +the following mount operation using
> +.BR mount (2):
> +.P
> +.in +4n
> +.EX
> +mount("/var", "/mnt", NULL, MS_BIND | MS_REC, NULL);
> +.EE
> +.in
> +.P
> +One of the primary benefits of using
> +.BR open_tree ()
> +and
> +.BR move_mount (2)
> +over the traditional
> +.BR mount (2)
> +is that operating with
> +.IR dirfd -style
> +file descriptors is far easier and more intuitive.
> +.P
> +.in +4n
> +.EX
> +int srcfd = open_tree(100, "", AT_EMPTY_PATH | OPEN_TREE_CLONE);
> +move_mount(srcfd, "", 200, "foo", MOVE_MOUNT_F_EMPTY_PATH);
> +.EE
> +.in
> +.P
> +The above procedure is roughly equivalent to
> +the following mount operation using
> +.BR mount (2):
> +.P
> +.in +4n
> +.EX
> +mount("/proc/self/fd/100", "/proc/self/fd/200/foo", NULL, MS_BIND, NULL);
> +.EE
> +.in
> +.P
> +In addition, you can use the file descriptor returned by
> +.BR open_tree ()
> +as the
> +.I dirfd
> +argument to any "*at()" system calls:
> +.P
> +.in +4n
> +.EX
> +int dirfd, fd;
> +\&
> +dirfd = open_tree(AT_FDCWD, "/etc", OPEN_TREE_CLONE);
> +fd = openat(dirfd, "passwd", O_RDONLY);
> +fchmodat(dirfd, "shadow", 0000, 0);
> +close(dirfd);
> +close(fd);
> +/* The bind-mount is now destroyed. */
> +.EE
> +.in
> +.SH SEE ALSO
> +.BR fsconfig (2),
> +.BR fsmount (2),
> +.BR fsopen (2),
> +.BR fspick (2),
> +.BR mount (2),
> +.BR mount_setattr (2),
> +.BR move_mount (2),
> +.BR mount_namespaces (7)
>
> --
> 2.51.0
>
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 04/10] man/man2/fsconfig.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-21 9:26 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-4-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 22478 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:45AM +1000, Aleksa Sarai wrote:
> This is loosely based on the original documentation written by David
> Howells and later maintained by Christian Brauner, but has been
> rewritten to be more from a user perspective (as well as fixing a few
> critical mistakes).
>
> Co-authored-by: David Howells <dhowells@redhat.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Co-authored-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
> man/man2/fsconfig.2 | 727 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 727 insertions(+)
>
> diff --git a/man/man2/fsconfig.2 b/man/man2/fsconfig.2
> new file mode 100644
> index 0000000000000000000000000000000000000000..5a18e08c700ac93aa22c341b4134944ee3c38d0b
> --- /dev/null
> +++ b/man/man2/fsconfig.2
> @@ -0,0 +1,727 @@
> +.\" Copyright, the authors of the Linux man-pages project
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH fsconfig 2 (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +fsconfig \- configure new or existing filesystem context
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ,\~ \-lc )
> +.SH SYNOPSIS
> +.nf
> +.B #include <sys/mount.h>
> +.P
> +.BI "int fsconfig(int " fd ", unsigned int " cmd ,
> +.BI " const char *_Nullable " key ,
> +.BI " const void *_Nullable " value ", int " aux );
> +.fi
> +.SH DESCRIPTION
> +The
> +.BR fsconfig ()
> +system call is part of
> +the suite of file descriptor based mount facilities in Linux.
> +.P
> +.BR fsconfig ()
> +is used to supply parameters to
> +and issue commands against
> +the filesystem configuration context
> +associated with the file descriptor
> +.IR fd .
> +Filesystem configuration contexts can be created with
> +.BR fsopen (2)
> +or be instantiated from an extant filesystem instance with
> +.BR fspick (2).
> +.P
> +The
> +.I cmd
> +argument indicates the command to be issued.
> +Some commands supply parameters to the context
> +(equivalent to mount options specified with
> +.BR mount (8)),
> +while others are meta-operations on the filesystem context.
> +The list of valid
> +.I cmd
> +values are:
I think I would have this page split into one page per command.
I would keep an overview in this page, of the main system call, and the
descriptions of each subcommand would go into each separate page.
You could have a look at fcntl(2), which has been the most recent page
split, and let me know what you think.
Have a lovely day!
Alex
> +.RS
> +.TP
> +.B FSCONFIG_SET_FLAG
> +Set the flag parameter named by
> +.IR key .
> +.I value
> +must be NULL,
> +and
> +.I aux
> +must be 0.
> +.TP
> +.B FSCONFIG_SET_STRING
> +Set the string parameter named by
> +.I key
> +to the value specified by
> +.IR value .
> +.I value
> +points to a null-terminated string,
> +and
> +.I aux
> +must be 0.
> +.TP
> +.B FSCONFIG_SET_BINARY
> +Set the blob parameter named by
> +.I key
> +to the contents of the binary blob
> +specified by
> +.IR value .
> +.I value
> +points to
> +the start of a buffer
> +that is
> +.I aux
> +bytes in length.
> +.TP
> +.B FSCONFIG_SET_FD
> +Set the file parameter named by
> +.I key
> +to the open file description
> +referenced by the file descriptor
> +.IR aux .
> +.I value
> +must be NULL.
> +.IP
> +You may also use
> +.B \%FSCONFIG_SET_STRING
> +for file parameters,
> +with
> +.I value
> +set to a null-terminated string
> +containing a base-10 representation
> +of the file descriptor number.
> +This mechanism is primarily intended for compatibility
> +with older
> +.BR mount (2)-based
> +programs,
> +and only works for parameters
> +that
> +.I only
> +accept file descriptor arguments.
> +.TP
> +.B FSCONFIG_SET_PATH
> +Set the path parameter named by
> +.I key
> +to the object at a provided path,
> +resolved in a similar manner to
> +.BR openat (2).
> +.I value
> +points to a null-terminated pathname string,
> +and
> +.I aux
> +is equivalent to the
> +.I dirfd
> +argument to
> +.BR openat (2).
> +See
> +.BR openat (2)
> +for an explanation of the need for
> +.BR \%FSCONFIG_SET_PATH .
> +.IP
> +You may also use
> +.B \%FSCONFIG_SET_STRING
> +for path parameters,
> +the behaviour of which is equivalent to
> +.B \%FSCONFIG_SET_PATH
> +with
> +.I aux
> +set to
> +.BR \%AT_FDCWD .
> +.TP
> +.B FSCONFIG_SET_PATH_EMPTY
> +As with
> +.BR \%FSCONFIG_SET_PATH ,
> +except that if
> +.I value
> +is an empty string,
> +the file descriptor specified by
> +.I aux
> +is operated on directly
> +and may be any type of file
> +(not just a directory).
> +This is equivalent to the behaviour of
> +.B \%AT_EMPTY_PATH
> +with most "*at()" system calls.
> +If
> +.I aux
> +is
> +.BR \%AT_FDCWD ,
> +the parameter will be set to
> +the current working directory
> +of the calling process.
> +.TP
> +.B FSCONFIG_CMD_CREATE
> +This command instructs the filesystem driver
> +to instantiate an instance of the filesystem in the kernel
> +with the parameters specified in the filesystem configuration context.
> +.I key
> +and
> +.I value
> +must be NULL,
> +and
> +.I aux
> +must be 0.
> +.IP
> +This command can only be issued once
> +in the lifetime of a filesystem context.
> +If the operation succeeds,
> +the filesystem context
> +associated with file descriptor
> +.I fd
> +now references the created filesystem instance,
> +and is placed into a special "awaiting-mount" mode
> +that allows you to use
> +.BR fsmount (2)
> +to create a mount object from the filesystem instance.
> +.\" FS_CONTEXT_AWAITING_MOUNT is the term the kernel uses for this.
> +If the operation fails,
> +in most cases
> +the filesystem context is placed in a failed mode
> +and cannot be used for any further
> +.BR fsconfig ()
> +operations
> +(though you may still retrieve diagnostic messages
> +through the message retrieval interface,
> +as described in
> +the corresponding subsection of
> +.BR fsopen (2)).
> +.IP
> +This command can only be issued against
> +filesystem configuration contexts
> +that were created with
> +.BR fsopen (2).
> +In order to create a filesystem instance,
> +the calling process must have the
> +.B \%CAP_SYS_ADMIN
> +capability.
> +.IP
> +An important thing to be aware of is that
> +the Linux kernel will
> +.I silently
> +reuse extant filesystem instances
> +depending on the filesystem type
> +and the configured parameters
> +(each filesystem driver has
> +its own policy for
> +how filesystem instances are reused).
> +This means that
> +the filesystem instance "created" by
> +.B \%FSCONFIG_CMD_CREATE
> +may, in fact, be a reference
> +to an extant filesystem instance in the kernel.
> +(For reference,
> +this behaviour also applies to
> +.BR mount (2).)
> +.IP
> +One side-effect of this behaviour is that
> +if an extant filesystem instance is reused,
> +.I all
> +parameters configured
> +for this filesystem configuration context
> +are
> +.I silently ignored
> +(with the exception of the
> +.I ro
> +and
> +.I rw
> +flag parameters;
> +if the state of the read-only flag in the
> +extant filesystem instance and the filesystem configuration context
> +do not match, this operation will return
> +.BR EBUSY ).
> +This also means that
> +.BR \%FSCONFIG_CMD_RECONFIGURE
> +commands issued against
> +the "created" filesystem instance
> +will also affect any mount objects associated with
> +the extant filesystem instance.
> +.IP
> +Programs that need to ensure
> +that they create a new filesystem instance
> +with specific parameters
> +(notably, security-related parameters
> +such as
> +.I acl
> +to enable POSIX ACLs\[em]as described in
> +.BR acl (5))
> +should use
> +.B \%FSCONFIG_CMD_CREATE_EXCL
> +instead.
> +.TP
> +.BR FSCONFIG_CMD_CREATE_EXCL " (since Linux 6.6)"
> +.\" commit 22ed7ecdaefe0cac0c6e6295e83048af60435b13
> +.\" commit 84ab1277ce5a90a8d1f377707d662ac43cc0918a
> +As with
> +.BR \%FSCONFIG_CMD_CREATE ,
> +except that the kernel is instructed
> +to not reuse extant filesystem instances.
> +If the operation
> +would be forced to
> +reuse an extant filesystem instance,
> +this operation will return
> +.B EBUSY
> +instead.
> +.IP
> +As a result (unlike
> +.BR \%FSCONFIG_CMD_CREATE ),
> +if this operation succeeds
> +then the calling process can be sure that
> +all of the parameters successfully configured with
> +.BR fsconfig ()
> +will actually be applied
> +to the created filesystem instance.
> +.TP
> +.B FSCONFIG_CMD_RECONFIGURE
> +This command instructs the filesystem driver
> +to apply the parameters specified in the filesystem configuration context
> +to the extant filesystem instance
> +referenced by the filesystem configuration context.
> +.I key
> +and
> +.I value
> +must be NULL,
> +and
> +.I aux
> +must be 0.
> +.IP
> +This is primarily intended for use with
> +.BR fspick (2),
> +but may also be used to modify
> +the parameters of a filesystem instance
> +after
> +.BR \%FSCONFIG_CMD_CREATE
> +was used to create it
> +and a mount object was created using
> +.BR fsmount (2).
> +In order to reconfigure an extant filesystem instance,
> +the calling process must have the
> +.B CAP_SYS_ADMIN
> +capability.
> +.IP
> +If the operation succeeds,
> +the filesystem context is reset
> +but remains in reconfiguration mode
> +and thus can be reused for subsequent
> +.B \%FSCONFIG_CMD_RECONFIGURE
> +commands.
> +If the operation fails,
> +in most cases
> +the filesystem context is placed in a failed mode
> +and cannot be used for any further
> +.BR fsconfig ()
> +operations
> +(though you may still retrieve diagnostic messages
> +through the message retrieval interface,
> +as described in
> +the corresponding subsection of
> +.BR fsopen (2)).
> +.RE
> +.P
> +Parameters specified with
> +.BI FSCONFIG_SET_ *
> +do not take effect
> +until a corresponding
> +.B \%FSCONFIG_CMD_CREATE
> +or
> +.B \%FSCONFIG_CMD_RECONFIGURE
> +command is issued.
> +.SH RETURN VALUE
> +On success,
> +.BR fsconfig ()
> +returns 0.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +If an error occurs, the filesystem driver may provide
> +additional information about the error
> +through the message retrieval interface for filesystem configuration contexts.
> +This additional information can be retrieved at any time by calling
> +.BR read (2)
> +on the filesystem instance or filesystem configuration context
> +referenced by the file descriptor
> +.IR fd .
> +(See the "Message retrieval interface" subsection in
> +.BR fsopen (2)
> +for more details on the message format.)
> +.P
> +Even after an error occurs,
> +the filesystem configuration context is
> +.I not
> +invalidated,
> +and thus can still be used with other
> +.BR fsconfig ()
> +commands.
> +This means that users can probe support for filesystem parameters
> +on a per-parameter basis,
> +and adjust which parameters they wish to set.
> +.P
> +The error values given below result from
> +filesystem type independent errors.
> +Each filesystem type may have its own special errors
> +and its own special behavior.
> +See the Linux kernel source code for details.
> +.TP
> +.B EACCES
> +A component of a path
> +provided as a path parameter
> +was not searchable.
> +(See also
> +.BR path_resolution (7).)
> +.TP
> +.B EACCES
> +.B \%FSCONFIG_CMD_CREATE
> +was attempted
> +for a read-only filesystem
> +without specifying the
> +.RB ' ro '
> +flag parameter.
> +.TP
> +.B EACCES
> +A specified block device parameter
> +is located on a filesystem
> +mounted with the
> +.B \%MS_NODEV
> +option.
> +.TP
> +.B EBADF
> +The file descriptor given by
> +.I fd
> +(or possibly by
> +.IR aux ,
> +depending on the command)
> +is invalid.
> +.TP
> +.B EBUSY
> +The filesystem context associated with
> +.I fd
> +is in the wrong state
> +for the given command.
> +.TP
> +.B EBUSY
> +The filesystem instance cannot be reconfigured as read-only
> +with
> +.B \%FSCONFIG_CMD_RECONFIGURE
> +because some programs
> +still hold files open for writing.
> +.TP
> +.B EBUSY
> +A new filesystem instance was requested with
> +.B \%FSCONFIG_CMD_CREATE_EXCL
> +but a matching superblock already existed.
> +.TP
> +.B EFAULT
> +One of the pointer arguments
> +points to a location
> +outside the calling process's accessible address space.
> +.TP
> +.B EINVAL
> +.I fd
> +does not refer to
> +a filesystem configuration context
> +or filesystem instance.
> +.TP
> +.B EINVAL
> +One of the values of
> +.IR name ,
> +.IR value ,
> +and/or
> +.I aux
> +were set to a non-zero value when
> +.I cmd
> +required that they be zero
> +(or NULL).
> +.TP
> +.B EINVAL
> +The parameter named by
> +.I name
> +cannot be set
> +using the type specified with
> +.IR cmd .
> +.TP
> +.B EINVAL
> +One of the source parameters
> +referred to
> +an invalid superblock.
> +.TP
> +.B ELOOP
> +Too many links encountered
> +during pathname resolution
> +of a path argument.
> +.TP
> +.B ENAMETOOLONG
> +A path argument was longer than
> +.BR PATH_MAX .
> +.TP
> +.B ENOENT
> +A path argument had a non-existent component.
> +.TP
> +.B ENOENT
> +A path argument is an empty string,
> +but
> +.I cmd
> +is not
> +.BR \%FSCONFIG_SET_PATH_EMPTY .
> +.TP
> +.B ENOMEM
> +The kernel could not allocate sufficient memory to complete the operation.
> +.TP
> +.B ENOTBLK
> +The parameter named by
> +.I name
> +must be a block device,
> +but the provided parameter value was not a block device.
> +.TP
> +.B ENOTDIR
> +A component of the path prefix
> +of a path argument
> +was not a directory.
> +.TP
> +.B EOPNOTSUPP
> +The command given by
> +.I cmd
> +is not valid.
> +.TP
> +.B ENXIO
> +The major number
> +of a block device parameter
> +is out of range.
> +.TP
> +.B EPERM
> +The command given by
> +.I cmd
> +was
> +.BR \%FSCONFIG_CMD_CREATE ,
> +.BR \%FSCONFIG_CMD_CREATE_EXCL ,
> +or
> +.BR \%FSCONFIG_CMD_RECONFIGURE ,
> +but the calling process does not have the required
> +.B \%CAP_SYS_ADMIN
> +capability.
> +.SH STANDARDS
> +Linux.
> +.SH HISTORY
> +Linux 5.2.
> +.\" commit ecdab150fddb42fe6a739335257949220033b782
> +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> +glibc 2.36.
> +.SH NOTES
> +.SS Generic filesystem parameters
> +Each filesystem driver is responsible for
> +parsing most parameters specified with
> +.BR fsconfig (),
> +meaning that individual filesystems
> +may have very different behaviour
> +when encountering parameters with the same name.
> +In general,
> +you should not assume that the behaviour of
> +.BR fsconfig ()
> +when specifying a parameter to one filesystem type
> +will match the behaviour of the same parameter
> +with a different filesystem type.
> +.P
> +However,
> +the following generic parameters
> +apply to all filesystems and have unified behaviour.
> +They are set using the listed
> +.BI \%FSCONFIG_SET_ *
> +command.
> +.TP
> +\fIro\fP and \fIrw\fP (\fB\%FSCONFIG_SET_FLAG\fP)
> +Configure whether the filesystem instance is read-only.
> +.TP
> +\fIdirsync\fP (\fB\%FSCONFIG_SET_FLAG\fP)
> +Make directory changes on this filesystem instance synchronous.
> +.TP
> +\fIsync\fP and \fIasync\fP (\fB\%FSCONFIG_SET_FLAG\fP)
> +Configure whether writes on this filesystem instance
> +will be made synchronous
> +(as though the
> +.B O_SYNC
> +flag to
> +.BR open (2)
> +was specified for
> +all file opens in this filesystem instance).
> +.TP
> +\fIlazytime\fP and \fInolazytime\fP (\fB\%FSCONFIG_SET_FLAG\fP)
> +Configure whether to reduce on-disk updates
> +of inode timestamps on this filesystem instance
> +(as described in the
> +.B \%MS_LAZYTIME
> +section of
> +.BR mount (2)).
> +.TP
> +\fImand\fP and \fInomand\fP (\fB\%FSCONFIG_SET_FLAG\fP)
> +Configure whether the filesystem instance should permit mandatory locking.
> +Since Linux 5.15,
> +.\" commit f7e33bdbd6d1bdf9c3df8bba5abcf3399f957ac3
> +mandatory locking has been deprecated
> +and setting this flag is a no-op.
> +.TP
> +\fIsource\fP (\fB\%FSCONFIG_SET_STRING\fP)
> +This parameter is equivalent to the
> +.I source
> +parameter passed to
> +.BR mount (2)
> +for the same filesystem type,
> +and is usually the pathname of a block device
> +containing the filesystem.
> +This parameter may only be set once
> +per filesystem configuration context transaction.
> +.P
> +In addition,
> +any filesystem parameters associated with
> +Linux Security Modules (LSMs)
> +are also generic with respect to the underlying filesystem.
> +See the documentation for the LSM you wish to configure for more details.
> +.SH CAVEATS
> +.SS Filesystem parameter types
> +As a result of
> +each filesystem driver being responsible for
> +parsing most parameters specified with
> +.BR fsconfig (),
> +some filesystem drivers
> +may have unintuitive behaviour
> +with regards to which
> +.BI \%FSCONFIG_SET_ *
> +commands are permitted
> +to configure a given parameter.
> +.P
> +In order for
> +filesystem parameters to be backwards compatible with
> +.BR mount (2),
> +they must be parseable as strings;
> +this almost universally means that
> +.B \%FSCONFIG_SET_STRING
> +can also be used to configure them.
> +.\" Aleksa Sarai
> +.\" Theoretically, a filesystem could check fc->oldapi and refuse
> +.\" FSCONFIG_SET_STRING if the operation is coming from the new API, but no
> +.\" filesystems do this (and probably never will).
> +However, other
> +.BI \%FSCONFIG_SET_ *
> +commands need to be opted into
> +by each filesystem driver's parameter parser.
> +.P
> +One of the most user-visible instances of
> +this inconsistency is that
> +many filesystems do not support
> +configuring path parameters with
> +.B \%FSCONFIG_SET_PATH
> +(despite the name),
> +which can lead to somewhat confusing
> +.B EINVAL
> +errors.
> +(For example, the generic
> +.I source
> +parameter\[em]which is usually a path\[em]can only be configured
> +with
> +.BR \%FSCONFIG_SET_STRING .)
> +.P
> +When writing programs that use
> +.BR fsconfig ()
> +to configure parameters
> +with commands other than
> +.BR \%FSCONFIG_SET_STRING ,
> +users should verify
> +that the
> +.BI \%FSCONFIG_SET_ *
> +commands used to configure each parameter
> +are supported by the corresponding filesystem driver.
> +.\" Aleksa Sarai
> +.\" While this (quite confusing) inconsistency in behaviour is true today
> +.\" (and has been true since this was merged), this appears to mostly be an
> +.\" unintended consequence of filesystem drivers hand-coding fsparam parsing.
> +.\" Path parameters are the most eggregious causes of confusion. Hopefully we
> +.\" can make this no longer the case in a future kernel.
> +.SH EXAMPLES
> +To illustrate the different kinds of flags that can be configured with
> +.BR fsconfig (),
> +here are a few examples of some different filesystems being created:
> +.P
> +.in +4n
> +.EX
> +int fsfd, mntfd;
> +\&
> +fsfd = fsopen("tmpfs", FSOPEN_CLOEXEC);
> +fsconfig(fsfd, FSCONFIG_SET_FLAG, "inode64", NULL, 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "uid", "1234", 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "huge", "never", 0);
> +fsconfig(fsfd, FSCONFIG_SET_FLAG, "casefold", NULL, 0);
> +fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_NOEXEC);
> +move_mount(mntfd, "", AT_FDCWD, "/tmp", MOVE_MOUNT_F_EMPTY_PATH);
> +\&
> +fsfd = fsopen("erofs", FSOPEN_CLOEXEC);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "/dev/loop0", 0);
> +fsconfig(fsfd, FSCONFIG_SET_FLAG, "acl", NULL, 0);
> +fsconfig(fsfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
> +fsconfig(fsfd, FSCONFIG_CMD_CREATE_EXCL, NULL, NULL, 0);
> +mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_NOSUID);
> +move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> +.EE
> +.in
> +.P
> +Usually,
> +specifying the same parameter named by
> +.I key
> +multiple times with
> +.BR fsconfig ()
> +causes the parameter value to be replaced.
> +However, some filesystems may have unique behaviour:
> +.P
> +.in +4n
> +.EX
> +\&
> +int fsfd, mntfd;
> +int lowerdirfd = open("/o/ctr/lower1", O_DIRECTORY | O_CLOEXEC);
> +\&
> +fsfd = fsopen("overlay", FSOPEN_CLOEXEC);
> +/* "lowerdir+" appends to the lower dir stack each time. */
> +fsconfig(fsfd, FSCONFIG_SET_FD, "lowerdir+", NULL, lowerdirfd);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "lowerdir+", "/o/ctr/lower2", 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "lowerdir+", "/o/ctr/lower3", 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "lowerdir+", "/o/ctr/lower4", 0);
> +.\" fsconfig(fsfd, FSCONFIG_SET_PATH, "lowerdir+", "/o/ctr/lower5", AT_FDCWD);
> +.\" fsconfig(fsfd, FSCONFIG_SET_PATH_EMPTY, "lowerdir+", "", lowerdirfd);
> +.\" Aleksa Sarai: Hopefully these will also be supported in the future.
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "xino", "auto", 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "nfs_export", "off", 0);
> +fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
> +move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> +.EE
> +.in
> +.P
> +And here is an example of how
> +.BR fspick (2)
> +can be used with
> +.BR fsconfig ()
> +to reconfigure the parameters
> +of an extant filesystem instance
> +attached to
> +.IR /proc :
> +.P
> +.in +4n
> +.EX
> +int fsfd = fspick(AT_FDCWD, "/proc", FSPICK_CLOEXEC);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "hidepid", "ptraceable", 0);
> +fsconfig(fsfd, FSCONFIG_SET_STRING, "subset", "pid", 0);
> +fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0);
> +.EE
> +.in
> +.SH SEE ALSO
> +.BR fsmount (2),
> +.BR fsopen (2),
> +.BR fspick (2),
> +.BR mount (2),
> +.BR mount_setattr (2),
> +.BR move_mount (2),
> +.BR open_tree (2),
> +.BR mount_namespaces (7)
> +
>
> --
> 2.51.0
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 03/10] man/man2/fspick.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-21 8:53 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <20250919-new-mount-api-v4-3-1261201ab562@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 10367 bytes --]
Hi Aleksa,
On Fri, Sep 19, 2025 at 11:59:44AM +1000, Aleksa Sarai wrote:
> This is loosely based on the original documentation written by David
> Howells and later maintained by Christian Brauner, but has been
> rewritten to be more from a user perspective (as well as fixing a few
> critical mistakes).
>
> Co-authored-by: David Howells <dhowells@redhat.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Co-authored-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
> man/man2/fspick.2 | 342 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 342 insertions(+)
>
> diff --git a/man/man2/fspick.2 b/man/man2/fspick.2
> new file mode 100644
> index 0000000000000000000000000000000000000000..1f87293f44658adeb7ab7cffebcac3174888f040
> --- /dev/null
> +++ b/man/man2/fspick.2
> @@ -0,0 +1,342 @@
> +.\" Copyright, the authors of the Linux man-pages project
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH fspick 2 (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +fspick \- select filesystem for reconfiguration
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ,\~ \-lc )
> +.SH SYNOPSIS
> +.nf
> +.BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */"
> +.B #include <sys/mount.h>
> +.P
> +.BI "int fspick(int " dirfd ", const char *" path ", unsigned int " flags );
> +.fi
> +.SH DESCRIPTION
> +The
> +.BR fspick ()
> +system call is part of
> +the suite of file descriptor based mount facilities in Linux.
> +.P
> +.BR fspick()
> +creates a new filesystem configuration context
> +for the extant filesystem instance
> +associated with the path described by
> +.IR dirfd
> +and
> +.IR path ,
> +places it into reconfiguration mode
> +(similar to
> +.BR mount (8)
> +with the
> +.I -o remount
> +option).
> +A new file descriptor
> +associated with the filesystem configuration context
> +is then returned.
> +The calling process must have the
> +.BR CAP_SYS_ADMIN
This should use '.B. (Bold). BR means alternating Bold and Roman, but
this only has one token, so it can't alternate.
If you run `make -R build-catman-troff`, this will trigger a diagnostic:
an.tmac: <page>:<line>: style: .BR expects at least 2 arguments, got 1
> +capability in order to create a new filesystem configuration context.
> +.P
> +The resultant file descriptor can be used with
> +.BR fsconfig (2)
> +to specify the desired set of changes to
> +filesystem parameters of the filesystem instance.
> +Once the desired set of changes have been configured,
> +the changes can be effectuated by calling
> +.BR fsconfig (2)
> +with the
> +.B \%FSCONFIG_CMD_RECONFIGURE
> +command.
> +Please note that\[em]in contrast to
> +the behaviour of
> +.B MS_REMOUNT
> +with
> +.BR mount (2)\[em] fspick ()
Only have one important keyword per macro call. In this case, I prefer
em dashes to only be attached to one side, as if they were parentheses,
so we don't need any tricks:
Please note that
\[em]in contrast to
...
.BR mount (2)\[em]
.BR fspick ()
> +instantiates the filesystem configuration context
> +with a copy of
> +the extant filesystem's filesystem parameters,
> +meaning that a subsequent
> +.B \%FSCONFIG_CMD_RECONFIGURE
> +operation
> +will only update filesystem parameters
> +explicitly modified with
> +.BR fsconfig (2).
> +.P
> +As with "*at()" system calls,
> +.BR fspick ()
> +uses the
> +.I dirfd
> +argument in conjunction with the
> +.I path
> +argument to determine the path to operate on, as follows:
> +.IP \[bu] 3
> +If the pathname given in
> +.I path
> +is absolute, then
> +.I dirfd
> +is ignored.
> +.IP \[bu]
> +If the pathname given in
> +.I path
> +is relative and
> +.I dirfd
> +is the special value
> +.BR \%AT_FDCWD ,
> +then
> +.I path
> +is interpreted relative to
> +the current working directory
> +of the calling process (like
> +.BR open (2)).
> +.IP \[bu]
> +If the pathname given in
> +.I path
> +is relative,
> +then it is interpreted relative to
> +the directory referred to by the file descriptor
> +.I dirfd
> +(rather than relative to
> +the current working directory
> +of the calling process,
> +as is done by
> +.BR open (2)
> +for a relative pathname).
> +In this case,
> +.I dirfd
> +must be a directory
> +that was opened for reading
> +.RB ( O_RDONLY )
> +or using the
> +.B O_PATH
> +flag.
> +.IP \[bu]
> +If
> +.I path
> +is an empty string,
> +and
> +.I flags
> +contains
> +.BR \%FSPICK_EMPTY_PATH ,
> +then the file descriptor
> +.I dirfd
> +is operated on directly.
> +In this case,
> +.I dirfd
> +may refer to any type of file,
> +not just a directory.
> +.P
> +See
> +.BR openat (2)
> +for an explanation of why the
> +.I dirfd
> +argument is useful.
> +.P
> +.I flags
> +can be used to control aspects of how
> +.I path
> +is resolved and
> +properties of the returned file descriptor.
> +A value for
> +.I flags
> +is constructed by bitwise ORing
> +zero or more of the following constants:
> +.RS
> +.TP
> +.B FSPICK_CLOEXEC
> +Set the close-on-exec
> +.RB ( FD_CLOEXEC )
> +flag on the new file descriptor.
> +See the description of the
> +.B O_CLOEXEC
> +flag in
> +.BR open (2)
> +for reasons why this may be useful.
> +.TP
> +.B FSPICK_EMPTY_PATH
> +If
> +.I path
> +is an empty string,
> +operate on the file referred to by
> +.I dirfd
> +(which may have been obtained from
> +.BR open (2),
> +.BR fsmount (2),
> +or
> +.BR open_tree (2)).
> +In this case,
> +.I dirfd
> +may refer to any type of file,
> +not just a directory.
> +If
> +.I dirfd
> +is
> +.BR \%AT_FDCWD ,
> +.BR fspick ()
> +will operate on the current working directory
> +of the calling process.
> +.TP
> +.B FSPICK_SYMLINK_NOFOLLOW
> +Do not follow symbolic links
> +in the terminal component of
> +.IR path .
> +If
> +.I path
> +references a symbolic link,
> +the returned filesystem context will reference
> +the filesystem that the symbolic link itself resides on.
> +.TP
> +.B FSPICK_NO_AUTOMOUNT
> +Do not automount any automount points encountered
> +while resolving
> +.IR path .
> +This allows you to reconfigure an automount point,
> +rather than the location that would be mounted.
> +This flag has no effect if
> +the automount point has already been mounted over.
I'll amend other similar issues if I find them, but in general, I'd put
the 'if' in the next line, as it is more tied to that part of the
sentence (think for example that if you reversed the sentence to say
"if ..., then ...", you'd move the 'if' with what follows it. You don't
need to search for all of these and fix them; just keep it in mind for
next time. In general I like the break points you used.
Have a lovely day!
Alex
> +.RE
> +.P
> +As with filesystem contexts created with
> +.BR fsopen (2),
> +the file descriptor returned by
> +.BR fspick ()
> +may be queried for message strings at any time by calling
> +.BR read (2)
> +on the file descriptor.
> +(See the "Message retrieval interface" subsection in
> +.BR fsopen (2)
> +for more details on the message format.)
> +.SH RETURN VALUE
> +On success, a new file descriptor is returned.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Search permission is denied
> +for one of the directories
> +in the path prefix of
> +.IR path .
> +(See also
> +.BR path_resolution (7).)
> +.TP
> +.B EBADF
> +.I path
> +is relative but
> +.I dirfd
> +is neither
> +.B \%AT_FDCWD
> +nor a valid file descriptor.
> +.TP
> +.B EFAULT
> +.I path
> +is NULL
> +or a pointer to a location
> +outside the calling process's accessible address space.
> +.TP
> +.B EINVAL
> +Invalid flag specified in
> +.IR flags .
> +.TP
> +.B ELOOP
> +Too many symbolic links encountered when resolving
> +.IR path .
> +.TP
> +.B EMFILE
> +The calling process has too many open files to create more.
> +.TP
> +.B ENAMETOOLONG
> +.I path
> +is longer than
> +.BR PATH_MAX .
> +.TP
> +.B ENFILE
> +The system has too many open files to create more.
> +.TP
> +.B ENOENT
> +A component of
> +.I path
> +does not exist,
> +or is a dangling symbolic link.
> +.TP
> +.B ENOENT
> +.I path
> +is an empty string, but
> +.B \%FSPICK_EMPTY_PATH
> +is not specified in
> +.IR flags .
> +.TP
> +.B ENOTDIR
> +A component of the path prefix of
> +.I path
> +is not a directory;
> +or
> +.I path
> +is relative and
> +.I dirfd
> +is a file descriptor referring to a file other than a directory.
> +.TP
> +.B ENOMEM
> +The kernel could not allocate sufficient memory to complete the operation.
> +.TP
> +.B EPERM
> +The calling process does not have the required
> +.B \%CAP_SYS_ADMIN
> +capability.
> +.SH STANDARDS
> +Linux.
> +.SH HISTORY
> +Linux 5.2.
> +.\" commit cf3cba4a429be43e5527a3f78859b1bfd9ebc5fb
> +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> +glibc 2.36.
> +.SH EXAMPLES
> +The following example sets the read-only flag
> +on the filesystem instance referenced by
> +the mount object attached at
> +.IR /tmp .
> +.P
> +.in +4n
> +.EX
> +int fsfd = fspick(AT_FDCWD, "/tmp", FSPICK_CLOEXEC);
> +fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
> +fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0);
> +.EE
> +.in
> +.P
> +The above procedure is roughly equivalent to
> +the following mount operation using
> +.BR mount (2):
> +.P
> +.in +4n
> +.EX
> +mount(NULL, "/tmp", NULL, MS_REMOUNT | MS_RDONLY, NULL);
> +.EE
> +.in
> +.P
> +With the notable caveat that
> +in this example,
> +.BR mount (2)
> +will clear all other filesystem parameters
> +(such as
> +.B MS_NOSUID
> +or
> +.BR MS_NOEXEC );
> +.BR fsconfig (2)
> +will only modify the
> +.I ro
> +parameter.
> +.SH SEE ALSO
> +.BR fsconfig (2),
> +.BR fsmount (2),
> +.BR fsopen (2),
> +.BR mount (2),
> +.BR mount_setattr (2),
> +.BR move_mount (2),
> +.BR open_tree (2),
> +.BR mount_namespaces (7)
> +
>
> --
> 2.51.0
>
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 02/10] man/man2/fsopen.2: document "new" mount API
From: Alejandro Colomar @ 2025-09-21 8:39 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-09-21-washed-creative-tenure-nibs-hssPyL@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 299 bytes --]
Hi Aleksa,
On Sun, Sep 21, 2025 at 11:33:34AM +1000, Aleksa Sarai wrote:
> By the way, I'll wait for your review of all of the remaining man-pages
> before sending v5. Thanks!
Okay.
Have a lovely day!
Alex
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply
* Re: [PATCH v4 00/10] man2: document "new" mount API
From: Askar Safin @ 2025-09-21 2:43 UTC (permalink / raw)
To: cyphar
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, safinaskar,
viro
In-Reply-To: <20250919-new-mount-api-v4-0-1261201ab562@cyphar.com>
Aleksa, thank you! Don't give up. We all need these manpages.
I see you didn't address some my previous notes.
* move_mount(2) still says "Mount objects cannot be attached beneath the filesystem root".
I suggest saying "root directory" or "root" or "root directory of the process" or just "/"
instead. But you may keep this phrase as is, of course.
* Docs for FSPICK_NO_AUTOMOUNT in fspick(2) are still wrong. They say that FSPICK_NO_AUTOMOUNT
affects all components of path. Similar thing applies to mount_setattr(2) and move_mount(2)
* open_tree(2) still says:
> If flags does not contain OPEN_TREE_CLONE, open_tree() returns a file descriptor
> that is exactly equivalent to one produced by openat(2) when called with the same dirfd and path.
This is not true if automounts are involved. I suggest adding "modulo automounts". But you may
keep everything, of course.
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v4 02/10] man/man2/fsopen.2: document "new" mount API
From: Aleksa Sarai @ 2025-09-21 1:33 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-09-19-movable-minty-stopper-posse-7AufW3@cyphar.com>
[-- Attachment #1: Type: text/plain, Size: 2257 bytes --]
On 2025-09-20, Aleksa Sarai <cyphar@cyphar.com> wrote:
> On 2025-09-19, Alejandro Colomar <alx@kernel.org> wrote:
> > Hi Aleksa,
> >
> > On Fri, Sep 19, 2025 at 11:59:43AM +1000, Aleksa Sarai wrote:
> > > This is loosely based on the original documentation written by David
> > > Howells and later maintained by Christian Brauner, but has been
> > > rewritten to be more from a user perspective (as well as fixing a few
> > > critical mistakes).
> > >
> > > Co-authored-by: David Howells <dhowells@redhat.com>
> > > Signed-off-by: David Howells <dhowells@redhat.com>
> > > Co-authored-by: Christian Brauner <brauner@kernel.org>
> > > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> > > ---
> > > man/man2/fsopen.2 | 384 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 384 insertions(+)
> > >
> > > diff --git a/man/man2/fsopen.2 b/man/man2/fsopen.2
> > > new file mode 100644
> > > index 0000000000000000000000000000000000000000..7cdbeac7d64b7e5c969dee619a039ec947d1e981
> > > --- /dev/null
> > > +++ b/man/man2/fsopen.2
> > > @@ -0,0 +1,384 @@
> > > +.\" Copyright, the authors of the Linux man-pages project
> > > +.\"
> > > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> > > +.\"
> > > +.TH fsopen 2 (date) "Linux man-pages (unreleased)"
> > > +.SH NAME
> > > +fsopen \- create a new filesystem context
> > > +.SH LIBRARY
> > > +Standard C library
> > > +.RI ( libc ,\~ \-lc )
> > > +.SH SYNOPSIS
> > > +.nf
> > > +.B #include <sys/mount.h>
> > > +.P
> > > +.BI "int fsopen(const char *" fsname ", unsigned int " flags );
> > > +.fi
> > > +.SH DESCRIPTION
> > > +The
> > > +.BR fsopen ()
> > > +system call is part of
> > > +the suite of file descriptor based mount facilities in Linux.
> >
> > Minor nitpick (I can amend that; no worries):
> >
> > Because 'file-descriptor-based' works as a single modifier of
> > facilities, it goes with hyphens.
>
> Will do for all of the new pages.
By the way, I'll wait for your review of all of the remaining man-pages
before sending v5. Thanks!
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
* Re: [PATCH RESEND 00/62] initrd: remove classic initrd support
From: Askar Safin @ 2025-09-20 3:54 UTC (permalink / raw)
To: Nicolas Schichan
Cc: akpm, andy.shevchenko, axboe, brauner, cyphar, devicetree,
ecurtin, email2tema, graf, gregkh, hca, hch, hsiangkao, initramfs,
jack, julian.stecklina, kees, linux-acpi, linux-alpha, linux-api,
linux-arch, linux-arm-kernel, linux-block, linux-csky, linux-doc,
linux-efi, linux-ext4, linux-fsdevel, linux-hexagon, linux-kernel,
linux-m68k, linux-mips, linux-openrisc, linux-parisc, linux-riscv,
linux-s390, linux-sh, linux-snps-arc, linux-um, linuxppc-dev,
loongarch, mcgrof, mingo, monstr, mzxreary, patches, rob,
sparclinux, thomas.weissschuh, thorsten.blum, torvalds, tytso,
viro, x86
In-Reply-To: <CAHNNwZAzecVcJXZmycX063-=p-M5jVkfStfgYVKJruOFo7y9zg@mail.gmail.com>
On Fri, Sep 19, 2025 at 6:25 PM Nicolas Schichan <nschichan@freebox.fr> wrote:
> Considering that the deprecation message didn't get displayed in some
> configurations, maybe it's a bit early at the very least.
I changed my opinion.
Breaking users, who did not see a deprecation message at all,
is unfair.
I will send a patchset soon, which will remove initrd codepath,
which currently contains deprecation notice. And I will put
deprecation notice to
other codepath.
Then in September 2026 I will fully remove initrd.
> SMTP server I used wasn't authenticated to google, so all gmail
> recipients were dropped. Hopefully this work better today.
Yes, this time I got your email
--
Askar Safin
^ permalink raw reply
* Re: [PATCH v4 02/10] man/man2/fsopen.2: document "new" mount API
From: Aleksa Sarai @ 2025-09-19 21:19 UTC (permalink / raw)
To: Alejandro Colomar
Cc: Michael T. Kerrisk, Alexander Viro, Jan Kara, Askar Safin,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <zrifsd6vqj6ve25uipyeteuztncgwtzfmfnfsxhcjwcnxf2wen@xjx3y2g77uin>
[-- Attachment #1: Type: text/plain, Size: 16729 bytes --]
On 2025-09-19, Alejandro Colomar <alx@kernel.org> wrote:
> Hi Aleksa,
>
> On Fri, Sep 19, 2025 at 11:59:43AM +1000, Aleksa Sarai wrote:
> > This is loosely based on the original documentation written by David
> > Howells and later maintained by Christian Brauner, but has been
> > rewritten to be more from a user perspective (as well as fixing a few
> > critical mistakes).
> >
> > Co-authored-by: David Howells <dhowells@redhat.com>
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > Co-authored-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> > ---
> > man/man2/fsopen.2 | 384 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 384 insertions(+)
> >
> > diff --git a/man/man2/fsopen.2 b/man/man2/fsopen.2
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..7cdbeac7d64b7e5c969dee619a039ec947d1e981
> > --- /dev/null
> > +++ b/man/man2/fsopen.2
> > @@ -0,0 +1,384 @@
> > +.\" Copyright, the authors of the Linux man-pages project
> > +.\"
> > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> > +.\"
> > +.TH fsopen 2 (date) "Linux man-pages (unreleased)"
> > +.SH NAME
> > +fsopen \- create a new filesystem context
> > +.SH LIBRARY
> > +Standard C library
> > +.RI ( libc ,\~ \-lc )
> > +.SH SYNOPSIS
> > +.nf
> > +.B #include <sys/mount.h>
> > +.P
> > +.BI "int fsopen(const char *" fsname ", unsigned int " flags );
> > +.fi
> > +.SH DESCRIPTION
> > +The
> > +.BR fsopen ()
> > +system call is part of
> > +the suite of file descriptor based mount facilities in Linux.
>
> Minor nitpick (I can amend that; no worries):
>
> Because 'file-descriptor-based' works as a single modifier of
> facilities, it goes with hyphens.
Will do for all of the new pages.
> > +.P
> > +.BR fsopen ()
> > +creates a blank filesystem configuration context within the kernel
> > +for the filesystem named by
> > +.I fsname
> > +and places it into creation mode.
> > +A new file descriptor
> > +associated with the filesystem configuration context
> > +is then returned.
> > +The calling process must have the
> > +.B \%CAP_SYS_ADMIN
> > +capability in order to create a new filesystem configuration context.
> > +.P
> > +A filesystem configuration context is
> > +an in-kernel representation of a pending transaction,
> > +containing a set of configuration parameters that are to be applied
> > +when creating a new instance of a filesystem
> > +(or modifying the configuration of an existing filesystem instance,
> > +such as when using
> > +.BR fspick (2)).
> > +.P
> > +After obtaining a filesystem configuration context with
> > +.BR fsopen (),
> > +the general workflow for operating on the context looks like the following:
> > +.IP (1) 5
> > +Pass the filesystem context file descriptor to
> > +.BR fsconfig (2)
> > +to specify any desired filesystem parameters.
> > +This may be done as many times as necessary.
> > +.IP (2)
> > +Pass the same filesystem context file descriptor to
> > +.BR fsconfig (2)
> > +with
> > +.B \%FSCONFIG_CMD_CREATE
> > +to create an instance of the configured filesystem.
> > +.IP (3)
> > +Pass the same filesystem context file descriptor to
> > +.BR fsmount (2)
> > +to create a new detached mount object for
> > +the root of the filesystem instance,
> > +which is then attached to a new file descriptor.
> > +(This also places the filesystem context file descriptor into
> > +reconfiguration mode,
> > +similar to the mode produced by
> > +.BR fspick (2).)
> > +Once a mount object has been created with
> > +.BR fsmount (2),
> > +the filesystem context file descriptor can be safely closed.
> > +.IP (4)
> > +Now that a mount object has been created,
> > +you may
> > +.RS
> > +.IP (4.1) 7
> > +use the detached mount object file descriptor as a
> > +.I dirfd
> > +argument to "*at()" system calls; and/or
> > +.IP (4.2) 7
>
> I'll paste here the formatted part of this page:
>
> (4) Now that a mount object has been created, you may
>
> (4.1) use the detached mount object file descrip‐
> tor as a dirfd argument to "*at()" system
> calls; and/or
>
> (4.2) attach the mount object to a mount point by
> passing the mount object file descriptor to
> move_mount(2). This will also prevent the
> mount object from being unmounted and de‐
> stroyed when the mount object file descrip‐
> tor is closed.
>
> The mount object file descriptor will remain asso‐
> ciated with the mount object even after doing the
> above operations, so you may repeatedly use the
> mount object file descriptor with move_mount(2)
> and/or "*at()" system calls as many times as neces‐
> sary.
>
> That sublist seems to be an unordered one. I think we should use
> a bullet list for those items (the outer list 1,2,3,4 is okay as is).
>
> Bullet lists
> Elements are preceded by bullet symbols (\[bu]).
> Anything that doesn't fit elsewhere is usually
> covered by this type of list.
I think I originally planned to reference the inner list (which would
require non-bullets), but it seems I dropped that text later. I'll fix
this up.
> > +attach the mount object to a mount point
> > +by passing the mount object file descriptor to
> > +.BR move_mount (2).
> > +This will also prevent the mount object from
> > +being unmounted and destroyed when
> > +the mount object file descriptor is closed.
> > +.RE
> > +.IP
> > +The mount object file descriptor will
> > +remain associated with the mount object
> > +even after doing the above operations,
> > +so you may repeatedly use the mount object file descriptor with
> > +.BR move_mount (2)
> > +and/or "*at()" system calls
> > +as many times as necessary.
> > +.P
> > +A filesystem context will move between different modes
> > +throughout its lifecycle
> > +(such as the creation phase
> > +when created with
> > +.BR fsopen (),
> > +the reconfiguration phase
> > +when an existing filesystem instance is selected with
> > +.BR fspick (2),
> > +and the intermediate "awaiting-mount" phase
> > +.\" FS_CONTEXT_AWAITING_MOUNT is the term the kernel uses for this.
> > +between
> > +.BR \%FSCONFIG_CMD_CREATE
> > +and
> > +.BR fsmount (2)),
> > +which has an impact on
> > +what operations are permitted on the filesystem context.
> > +.P
> > +The file descriptor returned by
> > +.BR fsopen ()
> > +also acts as a channel for filesystem drivers to
> > +provide more comprehensive diagnostic information
> > +than is normally provided through the standard
> > +.BR errno (3)
> > +interface for system calls.
> > +If an error occurs at any time during the workflow mentioned above,
> > +calling
> > +.BR read (2)
> > +on the filesystem context file descriptor
> > +will retrieve any ancillary information about the encountered errors.
> > +(See the "Message retrieval interface" section
> > +for more details on the message format.)
> > +.P
> > +.I flags
> > +can be used to control aspects of
> > +the creation of the filesystem configuration context file descriptor.
> > +A value for
> > +.I flags
> > +is constructed by bitwise ORing
> > +zero or more of the following constants:
> > +.RS
> > +.TP
> > +.B FSOPEN_CLOEXEC
> > +Set the close-on-exec
> > +.RB ( FD_CLOEXEC )
> > +flag on the new file descriptor.
> > +See the description of the
> > +.B O_CLOEXEC
> > +flag in
> > +.BR open (2)
> > +for reasons why this may be useful.
> > +.RE
> > +.P
> > +A list of filesystems supported by the running kernel
> > +(and thus a list of valid values for
> > +.IR fsname )
> > +can be obtained from
> > +.IR /proc/filesystems .
> > +(See also
> > +.BR proc_filesystems (5).)
> > +.SS Message retrieval interface
> > +When doing operations on a filesystem configuration context,
> > +the filesystem driver may choose to provide
> > +ancillary information to userspace
> > +in the form of message strings.
> > +.P
> > +The filesystem context file descriptors returned by
> > +.BR fsopen ()
> > +and
> > +.BR fspick (2)
> > +may be queried for message strings at any time by calling
> > +.BR read (2)
> > +on the file descriptor.
> > +Each call to
> > +.BR read (2)
> > +will return a single message,
> > +prefixed to indicate its class:
> > +.RS
> > +.TP
> > +\fBe\fP <\fImessage\fP>
>
> We don't use '<' and '>' for indicating variable parts. We already use
> italics for that. The reason to avoid the '<' and '>' is that it is
> confusing: it is often unclear if the '<' are literal or placeholders.
>
> We only use '<' when they're literal.
>
> I suspect your want
>
> .BI e\~ message
>
> BTW, I'm assuming there's one space between the letter and the message,
> and there are no literal '<'/'>', right?
No there aren't literal '<' / '>' characters, it's just a regular
string. I guess I was struggling with the (lack of) distinction between
using italics for variable names and things that are variable.
> Have a lovely day!
> Alex
>
> > +An error message was logged.
> > +This is usually associated with an error being returned
> > +from the corresponding system call which triggered this message.
> > +.TP
> > +\fBw\fP <\fImessage\fP>
> > +A warning message was logged.
> > +.TP
> > +\fBi\fP <\fImessage\fP>
> > +An informational message was logged.
> > +.RE
> > +.P
> > +Messages are removed from the queue as they are read.
> > +Note that the message queue has limited depth,
> > +so it is possible for messages to get lost.
> > +If there are no messages in the message queue,
> > +.B read(2)
> > +will return \-1 and
> > +.I errno
> > +will be set to
> > +.BR \%ENODATA .
> > +If the
> > +.I buf
> > +argument to
> > +.BR read (2)
> > +is not large enough to contain the entire message,
> > +.BR read (2)
> > +will return \-1 and
> > +.I errno
> > +will be set to
> > +.BR \%EMSGSIZE .
> > +(See BUGS.)
> > +.P
> > +If there are multiple filesystem contexts
> > +referencing the same filesystem instance
> > +(such as if you call
> > +.BR fspick (2)
> > +multiple times for the same mount),
> > +each one gets its own independent message queue.
> > +This does not apply to multiple file descriptors that are
> > +tied to the same underlying open file description
> > +(such as those created with
> > +.BR dup (2)).
> > +.P
> > +Message strings will usually be prefixed by
> > +the name of the filesystem or kernel subsystem
> > +that logged the message,
> > +though this may not always be the case.
> > +See the Linux kernel source code for details.
> > +.SH RETURN VALUE
> > +On success, a new file descriptor is returned.
> > +On error, \-1 is returned, and
> > +.I errno
> > +is set to indicate the error.
> > +.SH ERRORS
> > +.TP
> > +.B EFAULT
> > +.I fsname
> > +is NULL
> > +or a pointer to a location
> > +outside the calling process's accessible address space.
> > +.TP
> > +.B EINVAL
> > +.I flags
> > +had an invalid flag set.
> > +.TP
> > +.B EMFILE
> > +The calling process has too many open files to create more.
> > +.TP
> > +.B ENFILE
> > +The system has too many open files to create more.
> > +.TP
> > +.B ENODEV
> > +The filesystem named by
> > +.I fsname
> > +is not supported by the kernel.
> > +.TP
> > +.B ENOMEM
> > +The kernel could not allocate sufficient memory to complete the operation.
> > +.TP
> > +.B EPERM
> > +The calling process does not have the required
> > +.B \%CAP_SYS_ADMIN
> > +capability.
> > +.SH STANDARDS
> > +Linux.
> > +.SH HISTORY
> > +Linux 5.2.
> > +.\" commit 24dcb3d90a1f67fe08c68a004af37df059d74005
> > +.\" commit 400913252d09f9cfb8cce33daee43167921fc343
> > +glibc 2.36.
> > +.SH BUGS
> > +.SS Message retrieval interface and \fB\%EMSGSIZE\fP
> > +As described in the "Message retrieval interface" subsection above,
> > +calling
> > +.BR read (2)
> > +with too small a buffer to contain
> > +the next pending message in the message queue
> > +for the filesystem configuration context
> > +will cause
> > +.BR read (2)
> > +to return \-1 and set
> > +.BR errno (3)
> > +to
> > +.BR \%EMSGSIZE .
> > +.P
> > +However,
> > +this failed operation still
> > +consumes the message from the message queue.
> > +This effectively discards the message silently,
> > +as no data is copied into the
> > +.BR read (2)
> > +buffer.
> > +.P
> > +Programs should take care to ensure that
> > +their buffers are sufficiently large
> > +to contain any reasonable message string,
> > +in order to avoid silently losing valuable diagnostic information.
> > +.\" Aleksa Sarai
> > +.\" This unfortunate behaviour has existed since this feature was merged, but
> > +.\" I have sent a patchset which will finally fix it.
> > +.\" <https://lore.kernel.org/r/20250807-fscontext-log-cleanups-v3-1-8d91d6242dc3@cyphar.com/>
> > +.SH EXAMPLES
> > +To illustrate the workflow for creating a new mount,
> > +the following is an example of how to mount an
> > +.BR ext4 (5)
> > +filesystem stored on
> > +.I /dev/sdb1
> > +onto
> > +.IR /mnt .
> > +.P
> > +.in +4n
> > +.EX
> > +int fsfd, mntfd;
> > +\&
> > +fsfd = fsopen("ext4", FSOPEN_CLOEXEC);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_SET_PATH, "source", "/dev/sdb1", AT_FDCWD);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "noatime", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "acl", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "iversion", NULL, 0)
> > +fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> > +mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_RELATIME);
> > +move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
> > +.EE
> > +.in
> > +.P
> > +First,
> > +an ext4 configuration context is created and attached to the file descriptor
> > +.IR fsfd .
> > +Then, a series of parameters
> > +(such as the source of the filesystem)
> > +are provided using
> > +.BR fsconfig (2),
> > +followed by the filesystem instance being created with
> > +.BR \%FSCONFIG_CMD_CREATE .
> > +.BR fsmount (2)
> > +is then used to create a new mount object attached to the file descriptor
> > +.IR mntfd ,
> > +which is then attached to the intended mount point using
> > +.BR move_mount (2).
> > +.P
> > +The above procedure is functionally equivalent to
> > +the following mount operation using
> > +.BR mount (2):
> > +.P
> > +.in +4n
> > +.EX
> > +mount("/dev/sdb1", "/mnt", "ext4", MS_RELATIME,
> > + "ro,noatime,acl,user_xattr,iversion");
> > +.EE
> > +.in
> > +.P
> > +And here's an example of creating a mount object
> > +of an NFS server share
> > +and setting a Smack security module label.
> > +However, instead of attaching it to a mount point,
> > +the program uses the mount object directly
> > +to open a file from the NFS share.
> > +.P
> > +.in +4n
> > +.EX
> > +int fsfd, mntfd, fd;
> > +\&
> > +fsfd = fsopen("nfs", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "example.com/pub/linux", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_STRING, "nfsvers", "3", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_STRING, "rsize", "65536", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_STRING, "wsize", "65536", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_STRING, "smackfsdef", "foolabel", 0);
> > +fsconfig(fsfd, FSCONFIG_SET_FLAG, "rdma", NULL, 0);
> > +fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> > +mntfd = fsmount(fsfd, 0, MOUNT_ATTR_NODEV);
> > +fd = openat(mntfd, "src/linux-5.2.tar.xz", O_RDONLY);
> > +.EE
> > +.in
> > +.P
> > +Unlike the previous example,
> > +this operation has no trivial equivalent with
> > +.BR mount (2),
> > +as it was not previously possible to create a mount object
> > +that is not attached to any mount point.
> > +.SH SEE ALSO
> > +.BR fsconfig (2),
> > +.BR fsmount (2),
> > +.BR fspick (2),
> > +.BR mount (2),
> > +.BR mount_setattr (2),
> > +.BR move_mount (2),
> > +.BR open_tree (2),
> > +.BR mount_namespaces (7)
> >
> > --
> > 2.51.0
> >
>
> --
> <https://www.alejandro-colomar.es>
> Use port 80 (that is, <...:80/>).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]
^ permalink raw reply
page: next (older) | prev (newer) | latest
- recent:[subjects (threaded)|topics (new)|topics (active)]
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox