[PATCH v4 0/2] man-pages: add documentation for statmount/listmount

[PATCH v4 0/2] man-pages: add documentation for statmount/listmount

[Josef Bacik]

V3: https://lore.kernel.org/linux-fsdevel/cover.1719425922.git.josef@toxicpanda.com/
V2: https://lore.kernel.org/linux-fsdevel/cover.1719417184.git.josef@toxicpanda.com/
V1: https://lore.kernel.org/linux-fsdevel/cover.1719341580.git.josef@toxicpanda.com/

v3->v4:
- Addressed review comments.

v2->v3:
- Removed a spurious \t comment in listmount.2 (took me a while to figure out
  why it was needed in statmount.2 but not listmount.2, it's because it lets you
  know that there's a TS in the manpage).
- Fixed some unbalanced " in both pages
- Removed a EE in the nf section which is apparently not needed

v1->v2:
- Dropped the statx patch as Alejandro already took it (thanks!)
- Reworked everything to use semantic newlines
- Addressed all of the comments on the statmount.2 man page

Managed to get more of the build system running so hopefully this is all
formatted properly now.  Thanks,

Josef

Josef Bacik (2):
  statmount.2: New page describing the statmount syscall
  listmount.2: New page describing the listmount syscall

 man/man2/listmount.2 | 111 +++++++++++++++++
 man/man2/statmount.2 | 288 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 399 insertions(+)
 create mode 100644 man/man2/listmount.2
 create mode 100644 man/man2/statmount.2

-- 
2.43.0

[PATCH v4 1/2] statmount.2: New page describing the statmount syscall

[Josef Bacik]

Add some documentation on the new statmount syscall.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 man/man2/statmount.2 | 288 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 288 insertions(+)
 create mode 100644 man/man2/statmount.2

diff --git a/man/man2/statmount.2 b/man/man2/statmount.2
new file mode 100644
index 000000000..3e13107f5
--- /dev/null
+++ b/man/man2/statmount.2
@@ -0,0 +1,288 @@
+'\" t
+.\" Copyright (c) 2024 Josef Bacik <josef@toxicpanda.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH statmount 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+statmount \- get a mount status
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/mount.h>" "  /* Definition of STATMOUNT_* constants */"
+.B #include <unistd.h>
+.P
+.BI "int syscall(SYS_statmount, struct mnt_id_req * " req ,
+.BI "            struct statmount * " smbuf ", size_t " bufsize ,
+.BI "            unsigned long " flags );
+.P
+.B #include <linux/mount.h>
+.P
+.B struct mnt_id_req {
+.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
+.BR "    __u64 mnt_id;" "  /* The mnt_id being queried */"
+.BR "    __u64 param;" "   /* An ORed combination of the STATMOUNT_ constants */"
+.B };
+.P
+.B struct statmount {
+.B "    __u32 size;"
+.B "    __u64 mask;"
+.B "    __u32 sb_dev_major;"
+.B "    __u32 sb_dev_minor;"
+.B "    __u64 sb_magic;"
+.B "    __u32 sb_flags;"
+.B "    __u32 fs_type;"
+.B "    __u64 mnt_id;"
+.B "    __u64 mnt_parent_id;"
+.B "    __u32 mnt_id_old;"
+.B "    __u32 mnt_parent_id_old;"
+.B "    __u64 mnt_attr;"
+.B "    __u64 mnt_propagation;"
+.B "    __u64 mnt_peer_group;"
+.B "    __u64 mnt_master;"
+.B "    __u64 propagate_from;"
+.B "    __u32 mnt_root;"
+.B "    __u32 mnt_point;"
+.B "    char  str[];"
+.B };
+.fi
+.P
+.IR Note :
+glibc provides no wrapper for
+.BR statmount (),
+necessitating the use of
+.BR syscall (2).
+.SH DESCRIPTION
+To access a mount's status,
+you must have CAP_SYS_ADMIN in the user namespace.
+.P
+This function returns information about a mount,
+storing it in the buffer pointed to by
+.IR smbuf .
+The returned buffer is a
+.I struct statmount
+with the fields filled in as described below.
+.P
+(Note that reserved space and padding is omitted.)
+.SS The mnt_id_req structure
+.I req.size
+is used by the kernel to determine which struct
+.I mnt_id_req
+is being passed in,
+it should always be set to
+.IR sizeof(struct\~mnt_id_req) .
+.P
+.I req.mnt_id
+can be obtained from either
+.BR statx (2)
+using
+.B STATX_MNT_ID_UNIQUE
+or from
+.BR listmount (2)
+and is used as the identifier to query the status of the desired mount point.
+.P
+.I req.param
+is used to tell the kernel which fields the caller is interested in.
+It is an ORed combination of the following constants
+.P
+.in +4n
+.TS
+lBl.
+STATMOUNT_SB_BASIC	/* Want/got sb_* */
+STATMOUNT_MNT_BASIC	/* Want/got mnt_* */
+STATMOUNT_PROPAGATE_FROM	/* Want/got propagate_from */
+STATMOUNT_MNT_ROOT	/* Want/got mnt_root  */
+STATMOUNT_MNT_POINT	/* Want/got mnt_point */
+STATMOUNT_FS_TYPE	/* Want/got fs_type */
+.TE
+.in
+.P
+Note that,
+in general,
+the kernel does
+.I not
+reject values in
+.I req.param
+other than the above.
+(For an exception,
+see
+.B EINVAL
+in errors.)
+Instead,
+it simply informs the caller which values are supported
+by this kernel and filesystem via the
+.I statmount.mask
+field.
+Therefore,
+.I "do not"
+simply set
+.I req.param
+to
+.B UINT_MAX
+(all bits set),
+as one or more bits may,
+in the future,
+be used to specify an extension to the buffer.
+.SS The returned information
+The status information for the target mount is returned in the
+.I statmount
+structure pointed to by
+.IR smbuf .
+Included in this is
+.I size
+which indicates the size of the
+.I smbuf
+that was filled in,
+including any strings.
+.I mask
+which indicates what information in the structure has been filled in.
+.P
+It should be noted that the kernel may return fields that weren't requested
+and may fail to return fields that were requested,
+depending on what the backing file system and kernel supports.
+In either case,
+.I req.param
+will not be equal to
+.IR mask .
+.P
+The fields in the
+.I statmount
+structure are:
+.TP
+.I smbuf.size
+The size of the returned
+.I smbuf
+structure.
+.TP
+.I smbuf.mask
+The ORed combination of
+.B STATMOUNT_
+flags indicating which fields were filled in and thus valid.
+.TP
+.I smbuf.sb_dev_major
+.TQ
+.I smbuf.sb_dev_minor
+The device that is mounted at this mount point.
+.TP
+.I smbuf.sb_magic
+The file system specific super block magic.
+.TP
+.I smbuf.sb_flags
+The flags that are set on the super block,
+an ORed combination of
+.BR SB_RDONLY ,
+.BR SB_SYNCHRONOUS ,
+.BR SB_DIRSYNC ,
+.BR SB_LAZYTIME .
+.TP
+.I smbuf.fs_type
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mounted file system. It is
+a null-terminated string.
+.TP
+.I smbuf.mnt_id
+The unique mount ID of the mount.
+.TP
+.I smbuf.mnt_parent_id
+The unique mount ID of the parent mount point of this mount.
+If this is the root mount point then
+.IR smbuf.mnt_id\~==\~smbuf.parent_mount_id .
+.TP
+.I smbuf.mnt_id_old
+This corresponds to the mount ID that is exported by
+.IR /proc/ pid /mountinfo .
+.TP
+.I smbuf.mnt_parent_id_old
+This corresponds to the parent mount ID that is exported by
+.IR /proc/ pid /mountinfo .
+.TP
+.I smbuf.mnt_attr
+The
+.BI MOUNT_ATTR_ *
+flags set on this mount point.
+.TP
+.I smbuf.mnt_propagation
+The mount propagation flags,
+which can be one of
+.BR MS_SHARED ,
+.BR MS_SLAVE ,
+.BR MS_PRIVATE ,
+.BR MS_UNBINDABLE .
+.TP
+.I smbuf.mnt_peer_group
+The ID of the shared peer group.
+.TP
+.I smbuf.mnt_master
+The mount point receives its propagation from this mount ID.
+.TP
+.I smbuf.propagate_from
+The ID from the namespace we propagated from.
+.TP
+.I smbuf.mnt_root
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mount relative to the root
+of the file system.
+It is a NULL terminated string.
+.TP
+.I smbuf.mnt_point
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mount relative to the
+current root (ie if you are in a
+.BR chroot ).
+It is a NULL terminated string.
+.SH RETURN VALUE
+On success, zero is returned.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EPERM
+Permission is denied for accessing this mount.
+.TP
+.B EFAULT
+.I req
+or
+.I smbuf
+is NULL or points to a location outside the process's
+accessible address space.
+.TP
+.B EINVAL
+Invalid flag specified in
+.IR flags .
+.TP
+.B EINVAL
+.I req
+is of insufficient size to be utilized.
+.B E2BIG
+.I req
+is too large,
+the limit is the architectures page size.
+.TP
+.B EOVERFLOW
+The size of
+.I smbuf
+is too small to contain either the
+.IR smbuf.fs_type ,
+.IR smbuf.mnt_root ,
+or
+.IR smbuf.mnt_point .
+Allocate a larger buffer and retry the call.
+.TP
+.B ENOENT
+The specified
+.I req.mnt_id
+doesn't exist.
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.SH STANDARDS
+Linux.
+.SH SEE ALSO
+.BR listmount (2),
+.BR statx (2)
-- 
2.43.0

Re: [PATCH v4 1/2] statmount.2: New page describing the statmount syscall

[Alejandro Colomar]

[-- Attachment #1: Type: text/plain, Size: 9490 bytes --]

Hi Josef,

On Mon, Jul 01, 2024 at 09:37:53AM GMT, Josef Bacik wrote:
> Add some documentation on the new statmount syscall.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  man/man2/statmount.2 | 288 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 288 insertions(+)
>  create mode 100644 man/man2/statmount.2
> 
> diff --git a/man/man2/statmount.2 b/man/man2/statmount.2
> new file mode 100644
> index 000000000..3e13107f5
> --- /dev/null
> +++ b/man/man2/statmount.2
> @@ -0,0 +1,288 @@
> +'\" t
> +.\" Copyright (c) 2024 Josef Bacik <josef@toxicpanda.com>
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH statmount 2 (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +statmount \- get a mount status
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ", " \-lc )
> +.SH SYNOPSIS
> +.nf
> +.BR "#include <linux/mount.h>" "  /* Definition of STATMOUNT_* constants */"
> +.B #include <unistd.h>
> +.P
> +.BI "int syscall(SYS_statmount, struct mnt_id_req * " req ,
> +.BI "            struct statmount * " smbuf ", size_t " bufsize ,

Nothing in the page describes bufsize, AFAICS.

$ grep bufsize man/man2/statmount.2 | wc -l
1

> +.BI "            unsigned long " flags );
> +.P
> +.B #include <linux/mount.h>
> +.P
> +.B struct mnt_id_req {
> +.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
> +.BR "    __u64 mnt_id;" "  /* The mnt_id being queried */"
> +.BR "    __u64 param;" "   /* An ORed combination of the STATMOUNT_ constants */"
> +.B };
> +.P
> +.B struct statmount {
> +.B "    __u32 size;"
> +.B "    __u64 mask;"
> +.B "    __u32 sb_dev_major;"
> +.B "    __u32 sb_dev_minor;"
> +.B "    __u64 sb_magic;"
> +.B "    __u32 sb_flags;"
> +.B "    __u32 fs_type;"
> +.B "    __u64 mnt_id;"
> +.B "    __u64 mnt_parent_id;"
> +.B "    __u32 mnt_id_old;"
> +.B "    __u32 mnt_parent_id_old;"
> +.B "    __u64 mnt_attr;"
> +.B "    __u64 mnt_propagation;"
> +.B "    __u64 mnt_peer_group;"
> +.B "    __u64 mnt_master;"
> +.B "    __u64 propagate_from;"
> +.B "    __u32 mnt_root;"
> +.B "    __u32 mnt_point;"
> +.B "    char  str[];"
> +.B };
> +.fi
> +.P
> +.IR Note :
> +glibc provides no wrapper for
> +.BR statmount (),
> +necessitating the use of
> +.BR syscall (2).
> +.SH DESCRIPTION
> +To access a mount's status,
> +you must have CAP_SYS_ADMIN in the user namespace.

s/you/the caller/

> +.P
> +This function returns information about a mount,
> +storing it in the buffer pointed to by
> +.IR smbuf .
> +The returned buffer is a
> +.I struct statmount
> +with the fields filled in as described below.
> +.P
> +(Note that reserved space and padding is omitted.)
> +.SS The mnt_id_req structure
> +.I req.size
> +is used by the kernel to determine which struct
> +.I mnt_id_req

If you use 'struct\~foo', both words should be in italics.
You can do that, or make only 'foo' italics, and say foo structure.

> +is being passed in,

s/,/;/

> +it should always be set to
> +.IR sizeof(struct\~mnt_id_req) .
> +.P
> +.I req.mnt_id
> +can be obtained from either
> +.BR statx (2)
> +using
> +.B STATX_MNT_ID_UNIQUE
> +or from
> +.BR listmount (2)
> +and is used as the identifier to query the status of the desired mount point.
> +.P
> +.I req.param
> +is used to tell the kernel which fields the caller is interested in.
> +It is an ORed combination of the following constants
> +.P
> +.in +4n
> +.TS
> +lBl.

Let's put some space there:

lB l.

> +STATMOUNT_SB_BASIC	/* Want/got sb_* */
> +STATMOUNT_MNT_BASIC	/* Want/got mnt_* */
> +STATMOUNT_PROPAGATE_FROM	/* Want/got propagate_from */
> +STATMOUNT_MNT_ROOT	/* Want/got mnt_root  */
> +STATMOUNT_MNT_POINT	/* Want/got mnt_point */
> +STATMOUNT_FS_TYPE	/* Want/got fs_type */
> +.TE
> +.in
> +.P
> +Note that,

I'd remove the above, and start with "In general, ...".

Usually, everything is noteworthy, and if not, it should not go into the
documentation, or go into a footnote where it's marked as "unnecessary
on a first reading".  :)

See also:
<https://lore.kernel.org/linux-man/20230105225235.6cjtz6orjzxzvo6v@illithid/>

> +in general,
> +the kernel does
> +.I not
> +reject values in
> +.I req.param
> +other than the above.
> +(For an exception,
> +see
> +.B EINVAL
> +in errors.)
> +Instead,
> +it simply informs the caller which values are supported
> +by this kernel and filesystem via the
> +.I statmount.mask
> +field.
> +Therefore,
> +.I "do not"
> +simply set
> +.I req.param
> +to
> +.B UINT_MAX
> +(all bits set),
> +as one or more bits may,
> +in the future,
> +be used to specify an extension to the buffer.
> +.SS The returned information
> +The status information for the target mount is returned in the
> +.I statmount
> +structure pointed to by
> +.IR smbuf .

I think I'd move the text after this point to the descriptions of
smbuf.size and smbuf.mask.

> +Included in this is
> +.I size
> +which indicates the size of the
> +.I smbuf
> +that was filled in,
> +including any strings.
> +.I mask
> +which indicates what information in the structure has been filled in.

> +.P
> +It should be noted that the kernel may return fields that weren't requested

s/It should be noted that the/The/

For the reasons noted above.

> +and may fail to return fields that were requested,
> +depending on what the backing file system and kernel supports.
> +In either case,
> +.I req.param
> +will not be equal to
> +.IR mask .
> +.P
> +The fields in the
> +.I statmount
> +structure are:
> +.TP
> +.I smbuf.size
> +The size of the returned
> +.I smbuf
> +structure.
> +.TP
> +.I smbuf.mask
> +The ORed combination of
> +.B STATMOUNT_

.BI STATMOUNT_ *

> +flags indicating which fields were filled in and thus valid.
> +.TP
> +.I smbuf.sb_dev_major
> +.TQ
> +.I smbuf.sb_dev_minor
> +The device that is mounted at this mount point.
> +.TP
> +.I smbuf.sb_magic
> +The file system specific super block magic.
> +.TP
> +.I smbuf.sb_flags
> +The flags that are set on the super block,
> +an ORed combination of
> +.BR SB_RDONLY ,
> +.BR SB_SYNCHRONOUS ,
> +.BR SB_DIRSYNC ,
> +.BR SB_LAZYTIME .
> +.TP
> +.I smbuf.fs_type
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mounted file system. It is

New sentence, new line.

> +a null-terminated string.
> +.TP
> +.I smbuf.mnt_id
> +The unique mount ID of the mount.
> +.TP
> +.I smbuf.mnt_parent_id
> +The unique mount ID of the parent mount point of this mount.
> +If this is the root mount point then
> +.IR smbuf.mnt_id\~==\~smbuf.parent_mount_id .
> +.TP
> +.I smbuf.mnt_id_old
> +This corresponds to the mount ID that is exported by
> +.IR /proc/ pid /mountinfo .
> +.TP
> +.I smbuf.mnt_parent_id_old
> +This corresponds to the parent mount ID that is exported by
> +.IR /proc/ pid /mountinfo .
> +.TP
> +.I smbuf.mnt_attr
> +The
> +.BI MOUNT_ATTR_ *
> +flags set on this mount point.
> +.TP
> +.I smbuf.mnt_propagation
> +The mount propagation flags,
> +which can be one of
> +.BR MS_SHARED ,
> +.BR MS_SLAVE ,
> +.BR MS_PRIVATE ,
> +.BR MS_UNBINDABLE .
> +.TP
> +.I smbuf.mnt_peer_group
> +The ID of the shared peer group.
> +.TP
> +.I smbuf.mnt_master
> +The mount point receives its propagation from this mount ID.
> +.TP
> +.I smbuf.propagate_from
> +The ID from the namespace we propagated from.
> +.TP
> +.I smbuf.mnt_root
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mount relative to the root

I'd break the line right before "relative".

> +of the file system.
> +It is a NULL terminated string.
> +.TP
> +.I smbuf.mnt_point
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mount relative to the

I'd break the line right before "relative".

> +current root (ie if you are in a
> +.BR chroot ).
> +It is a NULL terminated string.
> +.SH RETURN VALUE
> +On success, zero is returned.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EPERM
> +Permission is denied for accessing this mount.
> +.TP
> +.B EFAULT
> +.I req
> +or
> +.I smbuf
> +is NULL or points to a location outside the process's
> +accessible address space.
> +.TP
> +.B EINVAL
> +Invalid flag specified in
> +.IR flags .
> +.TP
> +.B EINVAL
> +.I req
> +is of insufficient size to be utilized.
> +.B E2BIG
> +.I req
> +is too large,
> +the limit is the architectures page size.

I think the user should not know that the limit is a page size.
The user shall specify it as sizeof(struct mnt_id_req), and should
ignore any implementation details of the kernel.

So: "req is too large."

> +.TP
> +.B EOVERFLOW
> +The size of
> +.I smbuf
> +is too small to contain either the
> +.IR smbuf.fs_type ,
> +.IR smbuf.mnt_root ,
> +or
> +.IR smbuf.mnt_point .
> +Allocate a larger buffer and retry the call.
> +.TP
> +.B ENOENT
> +The specified
> +.I req.mnt_id
> +doesn't exist.
> +.TP
> +.B ENOMEM
> +Out of memory (i.e., kernel memory).
> +.SH STANDARDS
> +Linux.
> +.SH SEE ALSO
> +.BR listmount (2),
> +.BR statx (2)
> -- 
> 2.43.0

Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>

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[PATCH v4 2/2] listmount.2: New page describing the listmount syscall

[Josef Bacik]

Add some documentation for the new listmount syscall.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 man/man2/listmount.2 | 111 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 man/man2/listmount.2

diff --git a/man/man2/listmount.2 b/man/man2/listmount.2
new file mode 100644
index 000000000..a86f59a6d
--- /dev/null
+++ b/man/man2/listmount.2
@@ -0,0 +1,111 @@
+.\" Copyright (c) 2024 Josef Bacik <josef@toxicpanda.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH listmount 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+listmount \- get a list of mount ID's
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/mount.h>" "  /* Definition of struct mnt_id_req constants */"
+.B #include <unistd.h>
+.P
+.BI "int syscall(SYS_listmount, struct mnt_id_req * " req ,
+.BI "            u64 * " mnt_ids ", size_t " nr_mnt_ids ,
+.BI "            unsigned long " flags );
+.P
+.B #include <linux/mount.h>
+.P
+.B struct mnt_id_req {
+.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
+.BR "    __u64 mnt_id;" "  /* The parent mnt_id being searched */"
+.BR "    __u64 param;" "   /* The next mnt_id we want to find */"
+.B };
+.fi
+.P
+.IR Note :
+glibc provides no wrapper for
+.BR listmount (),
+necessitating the use of
+.BR syscall (2).
+.SH DESCRIPTION
+To access the mounts in your namespace,
+you must have CAP_SYS_ADMIN in the user namespace.
+.P
+This function returns a list of mount IDs under the
+.BR req.mnt_id .
+This is meant to be used in conjuction with
+.BR statmount (2)
+in order to provide a way to iterate and discover mounted file systems.
+.SS The mnt_id_req structure
+.I req.size
+is used by the kernel to determine which struct
+.I mnt_id_req
+is being passed in,
+it should always be set to sizeof(struct mnt_id req).
+.P
+.I req.mnt_id
+is the parent mnt_id that we will list from,
+which can either be
+.B LSMT_ROOT
+which means the root mount of the current mount namespace,
+or a mount ID obtained from either
+.BR statx (2)
+using
+.B STATX_MNT_ID_UNIQUE
+or from
+.BR listmount (2) .
+.P
+.I req.param
+is used to tell the kernel what mount ID to start the list from.
+This is useful if multiple calls to
+.BR listmount (2)
+are required.
+This can be set to the last mount ID returned + 1 in order to
+resume from a previous spot in the list.
+.SH RETURN VALUE
+On success, the number of entries filled into
+.I mnt_ids
+is returned, 0 if there are no more mounts left.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EPERM
+Permission is denied for accessing this mount.
+.TP
+.B EFAULT
+.I req
+or
+.I mnt_ids
+is NULL or points to a location outside the process's
+accessible address space.
+.TP
+.B EINVAL
+Invalid flag specified in
+.IR flags .
+.TP
+.B EINVAL
+.I req
+is of insufficient size to be utilized.
+.B E2BIG
+.I req
+is too large,
+the limit is the architectures page size.
+.TP
+.B ENOENT
+The specified
+.I req.mnt_id
+doesn't exist.
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.SH STANDARDS
+Linux.
+.SH SEE ALSO
+.BR statmount (2),
+.BR statx (2)
-- 
2.43.0