[PATCH v3] close_range.2: new page documenting close_range(2)

[PATCH v3] close_range.2: new page documenting close_range(2)

[Stephen Kitt]

This documents close_range(2) based on information in
278a5fbaed89dacd04e9d052f4594ffd0e0585de,
60997c3d45d9a67daf01c56d805ae4fec37e0bd8, and
582f1fb6b721facf04848d2ca57f34468da1813e.

Signed-off-by: Stephen Kitt <steve@sk2.org>
---
V3: fix synopsis overflow
    copy notes from membarrier.2 re the lack of wrapper
    semantic newlines
    drop non-standard "USE CASES" section heading
    add code example

V2: unsigned int to match the kernel declarations
    groff and grammar tweaks
    CLOSE_RANGE_UNSHARE unshares *and* closes
    Explain that EMFILE and ENOMEM can occur with C_R_U
    "Conforming to" phrasing
    Detailed explanation of CLOSE_RANGE_UNSHARE
    Reading /proc isn't common

 man2/close_range.2 | 266 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 266 insertions(+)
 create mode 100644 man2/close_range.2

diff --git a/man2/close_range.2 b/man2/close_range.2
new file mode 100644
index 000000000..f8f2053ac
--- /dev/null
+++ b/man2/close_range.2
@@ -0,0 +1,266 @@
+.\" Copyright (c) 2020 Stephen Kitt <steve@sk2.org>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual"
+.SH NAME
+close_range \- close all file descriptors in a given range
+.SH SYNOPSIS
+.nf
+.B #include <linux/close_range.h>
+.PP
+.BI "int close_range(unsigned int " first ", unsigned int " last ,
+.BI "                unsigned int " flags );
+.fi
+.PP
+.IR Note :
+There is no glibc wrapper for this system call; see NOTES.
+.SH DESCRIPTION
+The
+.BR close_range ()
+system call closes all open file descriptors from
+.I first
+to
+.I last
+(included).
+.PP
+Errors closing a given file descriptor are currently ignored.
+.PP
+.I flags
+can be 0 or set to one or both of the following:
+.TP
+.B CLOSE_RANGE_UNSHARE
+unshares the range of file descriptors from any other processes,
+before closing them,
+avoiding races with other threads sharing the file descriptor table.
+.TP
+.BR CLOSE_RANGE_CLOEXEC " (since Linux 5.10)"
+sets the close-on-exec bit instead of immediately closing the file
+descriptors.
+.SH RETURN VALUE
+On success,
+.BR close_range ()
+returns 0.
+On error, \-1 is returned and
+.I errno
+is set to indicate the cause of the error.
+.SH ERRORS
+.TP
+.B EINVAL
+.I flags
+is not valid, or
+.I first
+is greater than
+.IR last .
+.PP
+The following can occur with
+.B CLOSE_RANGE_UNSHARE
+(when constructing the new descriptor table):
+.TP
+.B EMFILE
+The per-process limit on the number of open file descriptors has been reached
+(see the description of
+.B RLIMIT_NOFILE
+in
+.BR getrlimit (2)).
+.TP
+.B ENOMEM
+Insufficient kernel memory was available.
+.SH VERSIONS
+.BR close_range ()
+first appeared in Linux 5.9.
+.SH CONFORMING TO
+.BR close_range ()
+is a nonstandard function that is also present on FreeBSD.
+.SH NOTES
+Glibc does not provide a wrapper for this system call; call it using
+.BR syscall (2).
+.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
+.SS Closing all open file descriptors
+To avoid blindly closing file descriptors in the range of possible
+file descriptors,
+this is sometimes implemented (on Linux) by listing open file
+descriptors in
+.I /proc/self/fd/
+and calling
+.BR close (2)
+on each one.
+.BR close_range ()
+can take care of this without requiring
+.I /proc
+and with a single system call,
+which provides significant performance benefits.
+.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
+.SS Closing file descriptors before exec
+File descriptors can be closed safely using
+.PP
+.in +4n
+.EX
+/* we don't want anything past stderr here */
+close_range(3, ~0U, CLOSE_RANGE_UNSHARE);
+execve(....);
+.EE
+.in
+.PP
+.B CLOSE_RANGE_UNSHARE
+is conceptually equivalent to
+.PP
+.in +4n
+.EX
+unshare(CLONE_FILES);
+close_range(first, last, 0);
+.EE
+.in
+.PP
+but can be more efficient:
+if the unshared range extends past the current maximum number of file
+descriptors allocated in the caller's file descriptor table
+(the common case when
+.I last
+is
+.BR ~0U ),
+the kernel will unshare a new file descriptor table for the caller up
+to
+.IR first .
+This avoids subsequent close calls entirely;
+the whole operation is complete once the table is unshared.
+.\" 582f1fb6b721facf04848d2ca57f34468da1813e
+.SS Closing files on \fBexec\fP
+This is particularly useful in cases where multiple
+.RB pre- exec
+setup steps risk conflicting with each other.
+For example, setting up a
+.BR seccomp (2)
+profile can conflict with a
+.B close_range
+call:
+if the file descriptors are closed before the seccomp profile is set
+up,
+the profile setup can't use them control their closure;
+if the file descriptors are closed afterwards,
+the seccomp profile can't block the
+.B close_range
+call or any fallbacks.
+Using
+.B CLOSE_RANGE_CLOEXEC
+avoids this:
+the descriptors can be marked before the seccomp profile is set up,
+and the profile can control access to
+.B close_range
+without affecting the calling process.
+.SH EXAMPLES
+The following program is designed to be execed by the second program
+below.
+It lists its open file descriptors:
+.PP
+.in +4n
+.EX
+/* listopen.c */
+
+#include <stdio.h>
+#include <sys/stat.h>
+
+int
+main(int argc, char *argv[])
+{
+    int i;
+    struct stat buf;
+
+    for (i = 0; i < 100; i++) {
+        if (!fstat(i, &buf))
+            printf("FD %d is open.\n", i);
+    }
+
+    exit(EXIT_SUCCESS);
+)
+.EE
+.in
+.PP
+This program executes the command given on its command-line after
+opening the files listed after the command,
+and then using
+.B close_range
+to close them:
+.PP
+.in +4n
+.EX
+/* close_range.c */
+
+#include <fcntl.h>
+#include <linux/close_range.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int
+main(int argc, char *argv[])
+{
+    char *newargv[] = { NULL };
+    char *newenviron[] = { NULL };
+    int i;
+
+    if (argc < 3) {
+        fprintf(stderr, "Usage: %s <command-to-run> <files-to-open>\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    for (i = 2; i < argc; i++) {
+        if (open(argv[i], O_RDONLY) == -1) {
+            perror(argv[i]);
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    if (syscall(__NR_close_range, 3, ~0U, CLOSE_RANGE_UNSHARE) == -1) {
+        perror("close_range");
+        exit(EXIT_FAILURE);
+    }
+
+    execve(argv[1], newargv, newenviron);
+    perror("execve");
+    exit(EXIT_FAILURE);
+}
+.EE
+.in
+.PP
+We can use the second program to exec the first as follows:
+.PP
+.in +4n
+.EX
+.RB "$" " make listopen close_range"
+.RB "$" " ./close_range ./listopen /dev/null /dev/zero"
+FD 0 is open.
+FD 1 is open.
+FD 2 is open.
+.EE
+.in
+.PP
+Removing the call to
+.B close_range
+will show different output, with the file descriptors for the named
+files still open.
+.SH SEE ALSO
+.BR close (2)

base-commit: b5dae3959625f5ff378e9edf9139057d1c06bb55
-- 
2.20.1

Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Alejandro Colomar (man-pages)]

Hi Stephen,

Please see some comments below.
It's looking good ;)

Thanks,

Alex

On 12/18/20 5:58 PM, Stephen Kitt wrote:
> This documents close_range(2) based on information in
> 278a5fbaed89dacd04e9d052f4594ffd0e0585de,
> 60997c3d45d9a67daf01c56d805ae4fec37e0bd8, and
> 582f1fb6b721facf04848d2ca57f34468da1813e.
> 
> Signed-off-by: Stephen Kitt <steve@sk2.org>
> ---
> V3: fix synopsis overflow
>     copy notes from membarrier.2 re the lack of wrapper
>     semantic newlines
>     drop non-standard "USE CASES" section heading
>     add code example
> 
> V2: unsigned int to match the kernel declarations
>     groff and grammar tweaks
>     CLOSE_RANGE_UNSHARE unshares *and* closes
>     Explain that EMFILE and ENOMEM can occur with C_R_U
>     "Conforming to" phrasing
>     Detailed explanation of CLOSE_RANGE_UNSHARE
>     Reading /proc isn't common
> 
>  man2/close_range.2 | 266 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 266 insertions(+)
>  create mode 100644 man2/close_range.2
> 
> diff --git a/man2/close_range.2 b/man2/close_range.2
> new file mode 100644
> index 000000000..f8f2053ac
> --- /dev/null
> +++ b/man2/close_range.2
> @@ -0,0 +1,266 @@
> +.\" Copyright (c) 2020 Stephen Kitt <steve@sk2.org>
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" Permission is granted to make and distribute verbatim copies of this
> +.\" manual provided the copyright notice and this permission notice are
> +.\" preserved on all copies.
> +.\"
> +.\" Permission is granted to copy and distribute modified versions of this
> +.\" manual under the conditions for verbatim copying, provided that the
> +.\" entire resulting derived work is distributed under the terms of a
> +.\" permission notice identical to this one.
> +.\"
> +.\" Since the Linux kernel and libraries are constantly changing, this
> +.\" manual page may be incorrect or out-of-date.  The author(s) assume no
> +.\" responsibility for errors or omissions, or for damages resulting from
> +.\" the use of the information contained herein.  The author(s) may not
> +.\" have taken the same level of care in the production of this manual,
> +.\" which is licensed free of charge, as they might when working
> +.\" professionally.
> +.\"
> +.\" Formatted or processed versions of this manual, if unaccompanied by
> +.\" the source, must acknowledge the copyright and authors of this work.
> +.\" %%%LICENSE_END
> +.\"
> +.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +close_range \- close all file descriptors in a given range
> +.SH SYNOPSIS
> +.nf
> +.B #include <linux/close_range.h>
> +.PP
> +.BI "int close_range(unsigned int " first ", unsigned int " last ,
> +.BI "                unsigned int " flags );
> +.fi
> +.PP
> +.IR Note :
> +There is no glibc wrapper for this system call; see NOTES.
> +.SH DESCRIPTION
> +The
> +.BR close_range ()
> +system call closes all open file descriptors from
> +.I first
> +to
> +.I last
> +(included).
> +.PP
> +Errors closing a given file descriptor are currently ignored.
> +.PP
> +.I flags
> +can be 0 or set to one or both of the following:
> +.TP
> +.B CLOSE_RANGE_UNSHARE
> +unshares the range of file descriptors from any other processes,
> +before closing them,
> +avoiding races with other threads sharing the file descriptor table.
> +.TP
> +.BR CLOSE_RANGE_CLOEXEC " (since Linux 5.10)"

|sort

I prefer alphabetic order rather than adding new items at the bottom.
When lists grow, it becomes difficult to find what you're looking for.

CLOEXEC should go before UNSHARE.

> +sets the close-on-exec bit instead of immediately closing the file
> +descriptors.

[
sets the close-on-exec bit instead of
immediately closing the file descriptors.
]

> +.SH RETURN VALUE
> +On success,
> +.BR close_range ()
> +returns 0.
> +On error, \-1 is returned and
> +.I errno
> +is set to indicate the cause of the error.
> +.SH ERRORS
> +.TP
> +.B EINVAL
> +.I flags
> +is not valid, or
> +.I first
> +is greater than
> +.IR last .
> +.PP
> +The following can occur with
> +.B CLOSE_RANGE_UNSHARE
> +(when constructing the new descriptor table):
> +.TP
> +.B EMFILE
> +The per-process limit on the number of open file descriptors has been reached
> +(see the description of
> +.B RLIMIT_NOFILE
> +in
> +.BR getrlimit (2)).
> +.TP
> +.B ENOMEM
> +Insufficient kernel memory was available.
> +.SH VERSIONS
> +.BR close_range ()
> +first appeared in Linux 5.9.
> +.SH CONFORMING TO
> +.BR close_range ()
> +is a nonstandard function that is also present on FreeBSD.
> +.SH NOTES
> +Glibc does not provide a wrapper for this system call; call it using
> +.BR syscall (2).
> +.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
> +.SS Closing all open file descriptors

The comment with the commit would be better inside the section it refers
to, so:

[
.SS Closing all open file descriptors
.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
]

> +To avoid blindly closing file descriptors in the range of possible
> +file descriptors,

[
To avoid blindly closing file descriptors
in the range of possible file descriptors,
]

> +this is sometimes implemented (on Linux) by listing open file
> +descriptors in

[
this is sometimes implemented (on Linux)
by listing open file descriptors in
]

> +.I /proc/self/fd/
> +and calling
> +.BR close (2)
> +on each one.
> +.BR close_range ()
> +can take care of this without requiring
> +.I /proc
> +and with a single system call,

s/with/within/

> +which provides significant performance benefits.
> +.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
> +.SS Closing file descriptors before exec

[
.SS Closing file descriptors before exec
.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
]

> +File descriptors can be closed safely using
> +.PP
> +.in +4n
> +.EX
> +/* we don't want anything past stderr here */
> +close_range(3, ~0U, CLOSE_RANGE_UNSHARE);
> +execve(....);> +.EE
> +.in
> +.PP
> +.B CLOSE_RANGE_UNSHARE
> +is conceptually equivalent to
> +.PP
> +.in +4n
> +.EX
> +unshare(CLONE_FILES);
> +close_range(first, last, 0);
> +.EE
> +.in
> +.PP
> +but can be more efficient:
> +if the unshared range extends past the current maximum number of file
> +descriptors allocated in the caller's file descriptor table

[
if the unshared range extends past
the current maximum number of file descriptors allocated
in the caller's file descriptor table
]

> +(the common case when
> +.I last
> +is
> +.BR ~0U ),

Literal values are not (usually) formatted.

[
.I last
is ~0U),
]

> +the kernel will unshare a new file descriptor table for the caller up
> +to

[
the kernel will unshare a new file descriptor table for the caller up to
]

> +.IR first .
> +This avoids subsequent close calls entirely;
> +the whole operation is complete once the table is unshared.
> +.\" 582f1fb6b721facf04848d2ca57f34468da1813e
> +.SS Closing files on \fBexec\fP

[
.SS Closing files on \fBexec\fP
.\" 582f1fb6b721facf04848d2ca57f34468da1813e
]

> +This is particularly useful in cases where multiple
> +.RB pre- exec
> +setup steps risk conflicting with each other.
> +For example, setting up a
> +.BR seccomp (2)
> +profile can conflict with a
> +.B close_range

.BR close_range ()

> +call:
> +if the file descriptors are closed before the seccomp profile is set

.BR seccomp (2)

> +up,

Please, split at a different point.

> +the profile setup can't use them control their closure;

I don't understand what you wanted to say.  them?

> +if the file descriptors are closed afterwards,
> +the seccomp profile can't block the
> +.B close_range

.BR close_range ()

> +call or any fallbacks.
> +Using
> +.B CLOSE_RANGE_CLOEXEC
> +avoids this:
> +the descriptors can be marked before the seccomp profile is set up,

.BR seccomp (2)

> +and the profile can control access to
> +.B close_range

.BR close_range ()

> +without affecting the calling process.
> +.SH EXAMPLES
> +The following program is designed to be execed by the second program
> +below.
> +It lists its open file descriptors:
> +.PP
> +.in +4n
> +.EX
> +/* listopen.c */
> +
> +#include <stdio.h>
> +#include <sys/stat.h>
> +
> +int
> +main(int argc, char *argv[])
> +{
> +    int i;

We use C99 declarations for loop indices.

> +    struct stat buf;
> +
> +    for (i = 0; i < 100; i++) {

    for (int i = 0; i < 100; i++) {

> +        if (!fstat(i, &buf))
> +            printf("FD %d is open.\n", i);

s/\\/\\e/

see: d1a719857b7eb68f5e5c1c965089038dee683240

I sometimes forget to fix those after copying the program to the page.
My solution is to copy the rendered text from the man page to a file
and then compile, and those errors become obvious ;)

> +    }
> +
> +    exit(EXIT_SUCCESS);
> +)
> +.EE
> +.in
> +.PP
> +This program executes the command given on its command-line after
> +opening the files listed after the command,
> +and then using

s/using/uses/

> +.B close_range

.BR close_range ()

> +to close them:
> +.PP
> +.in +4n
> +.EX
> +/* close_range.c */
> +
> +#include <fcntl.h>
> +#include <linux/close_range.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/stat.h>
> +#include <sys/syscall.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +int
> +main(int argc, char *argv[])
> +{
> +    char *newargv[] = { NULL };
> +    char *newenviron[] = { NULL };
> +    int i;

dd

> +
> +    if (argc < 3) {
> +        fprintf(stderr, "Usage: %s <command-to-run> <files-to-open>\n", argv[0]);

s/\\/\\e/

> +        exit(EXIT_FAILURE);
> +    }
> +
> +    for (i = 2; i < argc; i++) {

    for (int i = 2; i < argc; i++) {

> +        if (open(argv[i], O_RDONLY) == -1) {
> +            perror(argv[i]);
> +            exit(EXIT_FAILURE);
> +        }
> +    }
> +
> +    if (syscall(__NR_close_range, 3, ~0U, CLOSE_RANGE_UNSHARE) == -1) {
> +        perror("close_range");
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    execve(argv[1], newargv, newenviron);
> +    perror("execve");
> +    exit(EXIT_FAILURE);
> +}
> +.EE
> +.in
> +.PP
> +We can use the second program to exec the first as follows:
> +.PP
> +.in +4n
> +.EX
> +.RB "$" " make listopen close_range"
> +.RB "$" " ./close_range ./listopen /dev/null /dev/zero"
> +FD 0 is open.
> +FD 1 is open.
> +FD 2 is open.
> +.EE
> +.in
> +.PP
> +Removing the call to
> +.B close_range

.BR close_range ()

> +will show different output, with the file descriptors for the named
> +files still open.

[
will show different output,
with the file descriptors for the named files still open.
]

> +.SH SEE ALSO
> +.BR close (2)
> 
> base-commit: b5dae3959625f5ff378e9edf9139057d1c06bb55
> 

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/

Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Stephen Kitt]

[-- Attachment #1: Type: text/plain, Size: 12369 bytes --]

Hi Alex,

On Sat, 19 Dec 2020 15:00:00 +0100, "Alejandro Colomar (man-pages)"
<alx.manpages@gmail.com> wrote:
> Please see some comments below.
> It's looking good ;)

Thanks for your review and patience!

> On 12/18/20 5:58 PM, Stephen Kitt wrote:
> > This documents close_range(2) based on information in
> > 278a5fbaed89dacd04e9d052f4594ffd0e0585de,
> > 60997c3d45d9a67daf01c56d805ae4fec37e0bd8, and
> > 582f1fb6b721facf04848d2ca57f34468da1813e.
> > 
> > Signed-off-by: Stephen Kitt <steve@sk2.org>
> > ---
> > V3: fix synopsis overflow
> >     copy notes from membarrier.2 re the lack of wrapper
> >     semantic newlines
> >     drop non-standard "USE CASES" section heading
> >     add code example
> > 
> > V2: unsigned int to match the kernel declarations
> >     groff and grammar tweaks
> >     CLOSE_RANGE_UNSHARE unshares *and* closes
> >     Explain that EMFILE and ENOMEM can occur with C_R_U
> >     "Conforming to" phrasing
> >     Detailed explanation of CLOSE_RANGE_UNSHARE
> >     Reading /proc isn't common
> > 
> >  man2/close_range.2 | 266 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 266 insertions(+)
> >  create mode 100644 man2/close_range.2
> > 
> > diff --git a/man2/close_range.2 b/man2/close_range.2
> > new file mode 100644
> > index 000000000..f8f2053ac
> > --- /dev/null
> > +++ b/man2/close_range.2
> > @@ -0,0 +1,266 @@
> > +.\" Copyright (c) 2020 Stephen Kitt <steve@sk2.org>
> > +.\"
> > +.\" %%%LICENSE_START(VERBATIM)
> > +.\" Permission is granted to make and distribute verbatim copies of this
> > +.\" manual provided the copyright notice and this permission notice are
> > +.\" preserved on all copies.
> > +.\"
> > +.\" Permission is granted to copy and distribute modified versions of
> > this +.\" manual under the conditions for verbatim copying, provided that
> > the +.\" entire resulting derived work is distributed under the terms of a
> > +.\" permission notice identical to this one.
> > +.\"
> > +.\" Since the Linux kernel and libraries are constantly changing, this
> > +.\" manual page may be incorrect or out-of-date.  The author(s) assume no
> > +.\" responsibility for errors or omissions, or for damages resulting from
> > +.\" the use of the information contained herein.  The author(s) may not
> > +.\" have taken the same level of care in the production of this manual,
> > +.\" which is licensed free of charge, as they might when working
> > +.\" professionally.
> > +.\"
> > +.\" Formatted or processed versions of this manual, if unaccompanied by
> > +.\" the source, must acknowledge the copyright and authors of this work.
> > +.\" %%%LICENSE_END
> > +.\"
> > +.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual"
> > +.SH NAME
> > +close_range \- close all file descriptors in a given range
> > +.SH SYNOPSIS
> > +.nf
> > +.B #include <linux/close_range.h>
> > +.PP
> > +.BI "int close_range(unsigned int " first ", unsigned int " last ,
> > +.BI "                unsigned int " flags );
> > +.fi
> > +.PP
> > +.IR Note :
> > +There is no glibc wrapper for this system call; see NOTES.
> > +.SH DESCRIPTION
> > +The
> > +.BR close_range ()
> > +system call closes all open file descriptors from
> > +.I first
> > +to
> > +.I last
> > +(included).
> > +.PP
> > +Errors closing a given file descriptor are currently ignored.
> > +.PP
> > +.I flags
> > +can be 0 or set to one or both of the following:
> > +.TP
> > +.B CLOSE_RANGE_UNSHARE
> > +unshares the range of file descriptors from any other processes,
> > +before closing them,
> > +avoiding races with other threads sharing the file descriptor table.
> > +.TP
> > +.BR CLOSE_RANGE_CLOEXEC " (since Linux 5.10)"  
> 
> |sort
> 
> I prefer alphabetic order rather than adding new items at the bottom.
> When lists grow, it becomes difficult to find what you're looking for.
> 
> CLOEXEC should go before UNSHARE.

That makes sense.

> > +sets the close-on-exec bit instead of immediately closing the file
> > +descriptors.  
> 
> [
> sets the close-on-exec bit instead of
> immediately closing the file descriptors.
> ]

Is this for semantic reasons, or to balance the lines and make them easier to
read in the roff source?

> > +.SH RETURN VALUE
> > +On success,
> > +.BR close_range ()
> > +returns 0.
> > +On error, \-1 is returned and
> > +.I errno
> > +is set to indicate the cause of the error.
> > +.SH ERRORS
> > +.TP
> > +.B EINVAL
> > +.I flags
> > +is not valid, or
> > +.I first
> > +is greater than
> > +.IR last .
> > +.PP
> > +The following can occur with
> > +.B CLOSE_RANGE_UNSHARE
> > +(when constructing the new descriptor table):
> > +.TP
> > +.B EMFILE
> > +The per-process limit on the number of open file descriptors has been
> > reached +(see the description of
> > +.B RLIMIT_NOFILE
> > +in
> > +.BR getrlimit (2)).
> > +.TP
> > +.B ENOMEM
> > +Insufficient kernel memory was available.
> > +.SH VERSIONS
> > +.BR close_range ()
> > +first appeared in Linux 5.9.
> > +.SH CONFORMING TO
> > +.BR close_range ()
> > +is a nonstandard function that is also present on FreeBSD.
> > +.SH NOTES
> > +Glibc does not provide a wrapper for this system call; call it using
> > +.BR syscall (2).
> > +.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
> > +.SS Closing all open file descriptors  
> 
> The comment with the commit would be better inside the section it refers
> to, so:
> 
> [
> .SS Closing all open file descriptors
> .\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
> ]

Indeed!

> > +To avoid blindly closing file descriptors in the range of possible
> > +file descriptors,  
> 
> [
> To avoid blindly closing file descriptors
> in the range of possible file descriptors,
> ]
> 
> > +this is sometimes implemented (on Linux) by listing open file
> > +descriptors in  
> 
> [
> this is sometimes implemented (on Linux)
> by listing open file descriptors in
> ]
> 
> > +.I /proc/self/fd/
> > +and calling
> > +.BR close (2)
> > +on each one.
> > +.BR close_range ()
> > +can take care of this without requiring
> > +.I /proc
> > +and with a single system call,  
> 
> s/with/within/
> 
> > +which provides significant performance benefits.
> > +.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
> > +.SS Closing file descriptors before exec  
> 
> [
> .SS Closing file descriptors before exec
> .\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
> ]
> 
> > +File descriptors can be closed safely using
> > +.PP
> > +.in +4n
> > +.EX
> > +/* we don't want anything past stderr here */
> > +close_range(3, ~0U, CLOSE_RANGE_UNSHARE);  
> > +execve(....);> +.EE  
> > +.in
> > +.PP
> > +.B CLOSE_RANGE_UNSHARE
> > +is conceptually equivalent to
> > +.PP
> > +.in +4n
> > +.EX
> > +unshare(CLONE_FILES);
> > +close_range(first, last, 0);
> > +.EE
> > +.in
> > +.PP
> > +but can be more efficient:
> > +if the unshared range extends past the current maximum number of file
> > +descriptors allocated in the caller's file descriptor table  
> 
> [
> if the unshared range extends past
> the current maximum number of file descriptors allocated
> in the caller's file descriptor table
> ]
> 
> > +(the common case when
> > +.I last
> > +is
> > +.BR ~0U ),  
> 
> Literal values are not (usually) formatted.
> 
> [
> .I last
> is ~0U),
> ]
> 
> > +the kernel will unshare a new file descriptor table for the caller up
> > +to  
> 
> [
> the kernel will unshare a new file descriptor table for the caller up to
> ]
> 
> > +.IR first .
> > +This avoids subsequent close calls entirely;
> > +the whole operation is complete once the table is unshared.
> > +.\" 582f1fb6b721facf04848d2ca57f34468da1813e
> > +.SS Closing files on \fBexec\fP  
> 
> [
> .SS Closing files on \fBexec\fP
> .\" 582f1fb6b721facf04848d2ca57f34468da1813e
> ]
> 
> > +This is particularly useful in cases where multiple
> > +.RB pre- exec
> > +setup steps risk conflicting with each other.
> > +For example, setting up a
> > +.BR seccomp (2)
> > +profile can conflict with a
> > +.B close_range  
> 
> .BR close_range ()
> 
> > +call:
> > +if the file descriptors are closed before the seccomp profile is set  
> 
> .BR seccomp (2)
> 
> > +up,  
> 
> Please, split at a different point.
> 
> > +the profile setup can't use them control their closure;  
> 
> I don't understand what you wanted to say.  them?

Oops, I meant "the profile setup can't use them itself, or control their
closure".

> 
> > +if the file descriptors are closed afterwards,
> > +the seccomp profile can't block the
> > +.B close_range  
> 
> .BR close_range ()
> 
> > +call or any fallbacks.
> > +Using
> > +.B CLOSE_RANGE_CLOEXEC
> > +avoids this:
> > +the descriptors can be marked before the seccomp profile is set up,  
> 
> .BR seccomp (2)
> 
> > +and the profile can control access to
> > +.B close_range  
> 
> .BR close_range ()
> 
> > +without affecting the calling process.
> > +.SH EXAMPLES
> > +The following program is designed to be execed by the second program
> > +below.
> > +It lists its open file descriptors:
> > +.PP
> > +.in +4n
> > +.EX
> > +/* listopen.c */
> > +
> > +#include <stdio.h>
> > +#include <sys/stat.h>
> > +
> > +int
> > +main(int argc, char *argv[])
> > +{
> > +    int i;  
> 
> We use C99 declarations for loop indices.
> 
> > +    struct stat buf;
> > +
> > +    for (i = 0; i < 100; i++) {  
> 
>     for (int i = 0; i < 100; i++) {
> 
> > +        if (!fstat(i, &buf))
> > +            printf("FD %d is open.\n", i);  
> 
> s/\\/\\e/
> 
> see: d1a719857b7eb68f5e5c1c965089038dee683240
> 
> I sometimes forget to fix those after copying the program to the page.
> My solution is to copy the rendered text from the man page to a file
> and then compile, and those errors become obvious ;)

Ah yes, good catch. I was looking into automating checks for the source code
included in man pages throughout the project, but that throws a spanner in
the works!

> 
> > +    }
> > +
> > +    exit(EXIT_SUCCESS);
> > +)
> > +.EE
> > +.in
> > +.PP
> > +This program executes the command given on its command-line after
> > +opening the files listed after the command,
> > +and then using  
> 
> s/using/uses/
> 
> > +.B close_range  
> 
> .BR close_range ()
> 
> > +to close them:
> > +.PP
> > +.in +4n
> > +.EX
> > +/* close_range.c */
> > +
> > +#include <fcntl.h>
> > +#include <linux/close_range.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <sys/stat.h>
> > +#include <sys/syscall.h>
> > +#include <sys/types.h>
> > +#include <unistd.h>
> > +
> > +int
> > +main(int argc, char *argv[])
> > +{
> > +    char *newargv[] = { NULL };
> > +    char *newenviron[] = { NULL };
> > +    int i;  
> 
> dd
> 
> > +
> > +    if (argc < 3) {
> > +        fprintf(stderr, "Usage: %s <command-to-run> <files-to-open>\n",
> > argv[0]);  
> 
> s/\\/\\e/
> 
> > +        exit(EXIT_FAILURE);
> > +    }
> > +
> > +    for (i = 2; i < argc; i++) {  
> 
>     for (int i = 2; i < argc; i++) {
> 
> > +        if (open(argv[i], O_RDONLY) == -1) {
> > +            perror(argv[i]);
> > +            exit(EXIT_FAILURE);
> > +        }
> > +    }
> > +
> > +    if (syscall(__NR_close_range, 3, ~0U, CLOSE_RANGE_UNSHARE) == -1) {
> > +        perror("close_range");
> > +        exit(EXIT_FAILURE);
> > +    }
> > +
> > +    execve(argv[1], newargv, newenviron);
> > +    perror("execve");
> > +    exit(EXIT_FAILURE);
> > +}
> > +.EE
> > +.in
> > +.PP
> > +We can use the second program to exec the first as follows:
> > +.PP
> > +.in +4n
> > +.EX
> > +.RB "$" " make listopen close_range"
> > +.RB "$" " ./close_range ./listopen /dev/null /dev/zero"
> > +FD 0 is open.
> > +FD 1 is open.
> > +FD 2 is open.
> > +.EE
> > +.in
> > +.PP
> > +Removing the call to
> > +.B close_range  
> 
> .BR close_range ()
> 
> > +will show different output, with the file descriptors for the named
> > +files still open.  
> 
> [
> will show different output,
> with the file descriptors for the named files still open.
> ]

Thanks, I'll send a v4 with all the fixes above.

Regards,

Stephen

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Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Alejandro Colomar (man-pages)]

On 12/20/20 11:00 PM, Stephen Kitt wrote:
> Hi Alex,
> 
> On Sat, 19 Dec 2020 15:00:00 +0100, "Alejandro Colomar (man-pages)"
> <alx.manpages@gmail.com> wrote:
>> Please see some comments below.
>> It's looking good ;)
> 
> Thanks for your review and patience!
> 
>> On 12/18/20 5:58 PM, Stephen Kitt wrote:
>>> This documents close_range(2) based on information in
>>> 278a5fbaed89dacd04e9d052f4594ffd0e0585de,
>>> 60997c3d45d9a67daf01c56d805ae4fec37e0bd8, and
>>> 582f1fb6b721facf04848d2ca57f34468da1813e.
>>>
>>> Signed-off-by: Stephen Kitt <steve@sk2.org>
>>> ---
>>> V3: fix synopsis overflow
>>>     copy notes from membarrier.2 re the lack of wrapper
>>>     semantic newlines
>>>     drop non-standard "USE CASES" section heading
>>>     add code example
>>>
>>> V2: unsigned int to match the kernel declarations
>>>     groff and grammar tweaks
>>>     CLOSE_RANGE_UNSHARE unshares *and* closes
>>>     Explain that EMFILE and ENOMEM can occur with C_R_U
>>>     "Conforming to" phrasing
>>>     Detailed explanation of CLOSE_RANGE_UNSHARE
>>>     Reading /proc isn't common
>>>
>>>  man2/close_range.2 | 266 +++++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 266 insertions(+)
>>>  create mode 100644 man2/close_range.2
>>>
>>> diff --git a/man2/close_range.2 b/man2/close_range.2
>>> new file mode 100644
>>> index 000000000..f8f2053ac
>>> --- /dev/null
>>> +++ b/man2/close_range.2
>>> @@ -0,0 +1,266 @@
>>> +.\" Copyright (c) 2020 Stephen Kitt <steve@sk2.org>
>>> +.\"
>>> +.\" %%%LICENSE_START(VERBATIM)
>>> +.\" Permission is granted to make and distribute verbatim copies of this
>>> +.\" manual provided the copyright notice and this permission notice are
>>> +.\" preserved on all copies.
>>> +.\"
>>> +.\" Permission is granted to copy and distribute modified versions of
>>> this +.\" manual under the conditions for verbatim copying, provided that
>>> the +.\" entire resulting derived work is distributed under the terms of a
>>> +.\" permission notice identical to this one.
>>> +.\"
>>> +.\" Since the Linux kernel and libraries are constantly changing, this
>>> +.\" manual page may be incorrect or out-of-date.  The author(s) assume no
>>> +.\" responsibility for errors or omissions, or for damages resulting from
>>> +.\" the use of the information contained herein.  The author(s) may not
>>> +.\" have taken the same level of care in the production of this manual,
>>> +.\" which is licensed free of charge, as they might when working
>>> +.\" professionally.
>>> +.\"
>>> +.\" Formatted or processed versions of this manual, if unaccompanied by
>>> +.\" the source, must acknowledge the copyright and authors of this work.
>>> +.\" %%%LICENSE_END
>>> +.\"
>>> +.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual"
>>> +.SH NAME
>>> +close_range \- close all file descriptors in a given range
>>> +.SH SYNOPSIS
>>> +.nf
>>> +.B #include <linux/close_range.h>
>>> +.PP
>>> +.BI "int close_range(unsigned int " first ", unsigned int " last ,
>>> +.BI "                unsigned int " flags );
>>> +.fi
>>> +.PP
>>> +.IR Note :
>>> +There is no glibc wrapper for this system call; see NOTES.
>>> +.SH DESCRIPTION
>>> +The
>>> +.BR close_range ()
>>> +system call closes all open file descriptors from
>>> +.I first
>>> +to
>>> +.I last
>>> +(included).
>>> +.PP
>>> +Errors closing a given file descriptor are currently ignored.
>>> +.PP
>>> +.I flags
>>> +can be 0 or set to one or both of the following:
>>> +.TP
>>> +.B CLOSE_RANGE_UNSHARE
>>> +unshares the range of file descriptors from any other processes,
>>> +before closing them,
>>> +avoiding races with other threads sharing the file descriptor table.
>>> +.TP
>>> +.BR CLOSE_RANGE_CLOEXEC " (since Linux 5.10)"  
>>
>> |sort
>>
>> I prefer alphabetic order rather than adding new items at the bottom.
>> When lists grow, it becomes difficult to find what you're looking for.
>>
>> CLOEXEC should go before UNSHARE.
> 
> That makes sense.
> 
>>> +sets the close-on-exec bit instead of immediately closing the file
>>> +descriptors.  
>>
>> [
>> sets the close-on-exec bit instead of
>> immediately closing the file descriptors.
>> ]
> 
> Is this for semantic reasons, or to balance the lines and make them easier to
> read in the roff source?

B is also true, but mostly A.

Cheers,

Alex

> 
>>> +.SH RETURN VALUE
>>> +On success,
>>> +.BR close_range ()
>>> +returns 0.
>>> +On error, \-1 is returned and
>>> +.I errno
>>> +is set to indicate the cause of the error.
>>> +.SH ERRORS
>>> +.TP
>>> +.B EINVAL
>>> +.I flags
>>> +is not valid, or
>>> +.I first
>>> +is greater than
>>> +.IR last .
>>> +.PP
>>> +The following can occur with
>>> +.B CLOSE_RANGE_UNSHARE
>>> +(when constructing the new descriptor table):
>>> +.TP
>>> +.B EMFILE
>>> +The per-process limit on the number of open file descriptors has been
>>> reached +(see the description of
>>> +.B RLIMIT_NOFILE
>>> +in
>>> +.BR getrlimit (2)).
>>> +.TP
>>> +.B ENOMEM
>>> +Insufficient kernel memory was available.
>>> +.SH VERSIONS
>>> +.BR close_range ()
>>> +first appeared in Linux 5.9.
>>> +.SH CONFORMING TO
>>> +.BR close_range ()
>>> +is a nonstandard function that is also present on FreeBSD.
>>> +.SH NOTES
>>> +Glibc does not provide a wrapper for this system call; call it using
>>> +.BR syscall (2).
>>> +.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
>>> +.SS Closing all open file descriptors  
>>
>> The comment with the commit would be better inside the section it refers
>> to, so:
>>
>> [
>> .SS Closing all open file descriptors
>> .\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
>> ]
> 
> Indeed!
> 
>>> +To avoid blindly closing file descriptors in the range of possible
>>> +file descriptors,  
>>
>> [
>> To avoid blindly closing file descriptors
>> in the range of possible file descriptors,
>> ]
>>
>>> +this is sometimes implemented (on Linux) by listing open file
>>> +descriptors in  
>>
>> [
>> this is sometimes implemented (on Linux)
>> by listing open file descriptors in
>> ]
>>
>>> +.I /proc/self/fd/
>>> +and calling
>>> +.BR close (2)
>>> +on each one.
>>> +.BR close_range ()
>>> +can take care of this without requiring
>>> +.I /proc
>>> +and with a single system call,  
>>
>> s/with/within/
>>
>>> +which provides significant performance benefits.
>>> +.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
>>> +.SS Closing file descriptors before exec  
>>
>> [
>> .SS Closing file descriptors before exec
>> .\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8
>> ]
>>
>>> +File descriptors can be closed safely using
>>> +.PP
>>> +.in +4n
>>> +.EX
>>> +/* we don't want anything past stderr here */
>>> +close_range(3, ~0U, CLOSE_RANGE_UNSHARE);  
>>> +execve(....);> +.EE  
>>> +.in
>>> +.PP
>>> +.B CLOSE_RANGE_UNSHARE
>>> +is conceptually equivalent to
>>> +.PP
>>> +.in +4n
>>> +.EX
>>> +unshare(CLONE_FILES);
>>> +close_range(first, last, 0);
>>> +.EE
>>> +.in
>>> +.PP
>>> +but can be more efficient:
>>> +if the unshared range extends past the current maximum number of file
>>> +descriptors allocated in the caller's file descriptor table  
>>
>> [
>> if the unshared range extends past
>> the current maximum number of file descriptors allocated
>> in the caller's file descriptor table
>> ]
>>
>>> +(the common case when
>>> +.I last
>>> +is
>>> +.BR ~0U ),  
>>
>> Literal values are not (usually) formatted.
>>
>> [
>> .I last
>> is ~0U),
>> ]
>>
>>> +the kernel will unshare a new file descriptor table for the caller up
>>> +to  
>>
>> [
>> the kernel will unshare a new file descriptor table for the caller up to
>> ]
>>
>>> +.IR first .
>>> +This avoids subsequent close calls entirely;
>>> +the whole operation is complete once the table is unshared.
>>> +.\" 582f1fb6b721facf04848d2ca57f34468da1813e
>>> +.SS Closing files on \fBexec\fP  
>>
>> [
>> .SS Closing files on \fBexec\fP
>> .\" 582f1fb6b721facf04848d2ca57f34468da1813e
>> ]
>>
>>> +This is particularly useful in cases where multiple
>>> +.RB pre- exec
>>> +setup steps risk conflicting with each other.
>>> +For example, setting up a
>>> +.BR seccomp (2)
>>> +profile can conflict with a
>>> +.B close_range  
>>
>> .BR close_range ()
>>
>>> +call:
>>> +if the file descriptors are closed before the seccomp profile is set  
>>
>> .BR seccomp (2)
>>
>>> +up,  
>>
>> Please, split at a different point.
>>
>>> +the profile setup can't use them control their closure;  
>>
>> I don't understand what you wanted to say.  them?
> 
> Oops, I meant "the profile setup can't use them itself, or control their
> closure".
> 
>>
>>> +if the file descriptors are closed afterwards,
>>> +the seccomp profile can't block the
>>> +.B close_range  
>>
>> .BR close_range ()
>>
>>> +call or any fallbacks.
>>> +Using
>>> +.B CLOSE_RANGE_CLOEXEC
>>> +avoids this:
>>> +the descriptors can be marked before the seccomp profile is set up,  
>>
>> .BR seccomp (2)
>>
>>> +and the profile can control access to
>>> +.B close_range  
>>
>> .BR close_range ()
>>
>>> +without affecting the calling process.
>>> +.SH EXAMPLES
>>> +The following program is designed to be execed by the second program
>>> +below.
>>> +It lists its open file descriptors:
>>> +.PP
>>> +.in +4n
>>> +.EX
>>> +/* listopen.c */
>>> +
>>> +#include <stdio.h>
>>> +#include <sys/stat.h>
>>> +
>>> +int
>>> +main(int argc, char *argv[])
>>> +{
>>> +    int i;  
>>
>> We use C99 declarations for loop indices.
>>
>>> +    struct stat buf;
>>> +
>>> +    for (i = 0; i < 100; i++) {  
>>
>>     for (int i = 0; i < 100; i++) {
>>
>>> +        if (!fstat(i, &buf))
>>> +            printf("FD %d is open.\n", i);  
>>
>> s/\\/\\e/
>>
>> see: d1a719857b7eb68f5e5c1c965089038dee683240
>>
>> I sometimes forget to fix those after copying the program to the page.
>> My solution is to copy the rendered text from the man page to a file
>> and then compile, and those errors become obvious ;)
> 
> Ah yes, good catch. I was looking into automating checks for the source code
> included in man pages throughout the project, but that throws a spanner in
> the works!
> 
>>
>>> +    }
>>> +
>>> +    exit(EXIT_SUCCESS);
>>> +)
>>> +.EE
>>> +.in
>>> +.PP
>>> +This program executes the command given on its command-line after
>>> +opening the files listed after the command,
>>> +and then using  
>>
>> s/using/uses/
>>
>>> +.B close_range  
>>
>> .BR close_range ()
>>
>>> +to close them:
>>> +.PP
>>> +.in +4n
>>> +.EX
>>> +/* close_range.c */
>>> +
>>> +#include <fcntl.h>
>>> +#include <linux/close_range.h>
>>> +#include <stdio.h>
>>> +#include <stdlib.h>
>>> +#include <sys/stat.h>
>>> +#include <sys/syscall.h>
>>> +#include <sys/types.h>
>>> +#include <unistd.h>
>>> +
>>> +int
>>> +main(int argc, char *argv[])
>>> +{
>>> +    char *newargv[] = { NULL };
>>> +    char *newenviron[] = { NULL };
>>> +    int i;  
>>
>> dd
>>
>>> +
>>> +    if (argc < 3) {
>>> +        fprintf(stderr, "Usage: %s <command-to-run> <files-to-open>\n",
>>> argv[0]);  
>>
>> s/\\/\\e/
>>
>>> +        exit(EXIT_FAILURE);
>>> +    }
>>> +
>>> +    for (i = 2; i < argc; i++) {  
>>
>>     for (int i = 2; i < argc; i++) {
>>
>>> +        if (open(argv[i], O_RDONLY) == -1) {
>>> +            perror(argv[i]);
>>> +            exit(EXIT_FAILURE);
>>> +        }
>>> +    }
>>> +
>>> +    if (syscall(__NR_close_range, 3, ~0U, CLOSE_RANGE_UNSHARE) == -1) {
>>> +        perror("close_range");
>>> +        exit(EXIT_FAILURE);
>>> +    }
>>> +
>>> +    execve(argv[1], newargv, newenviron);
>>> +    perror("execve");
>>> +    exit(EXIT_FAILURE);
>>> +}
>>> +.EE
>>> +.in
>>> +.PP
>>> +We can use the second program to exec the first as follows:
>>> +.PP
>>> +.in +4n
>>> +.EX
>>> +.RB "$" " make listopen close_range"
>>> +.RB "$" " ./close_range ./listopen /dev/null /dev/zero"
>>> +FD 0 is open.
>>> +FD 1 is open.
>>> +FD 2 is open.
>>> +.EE
>>> +.in
>>> +.PP
>>> +Removing the call to
>>> +.B close_range  
>>
>> .BR close_range ()
>>
>>> +will show different output, with the file descriptors for the named
>>> +files still open.  
>>
>> [
>> will show different output,
>> with the file descriptors for the named files still open.
>> ]
> 
> Thanks, I'll send a v4 with all the fixes above.
> 
> Regards,
> 
> Stephen
> 

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/

Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Stephen Kitt]

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Hi Alex,

On Sat, 19 Dec 2020 15:00:00 +0100, "Alejandro Colomar (man-pages)"
<alx.manpages@gmail.com> wrote:
> On 12/18/20 5:58 PM, Stephen Kitt wrote:
[...]
> > +This program executes the command given on its command-line after
> > +opening the files listed after the command,
> > +and then using  
> 
> s/using/uses/

It’s the same form as “opening”: “after opening ... and then using”. The
overall sequence is “open”, “close_range”, “execve”.

Regards,

Stephen

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Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Alejandro Colomar (man-pages)]

Hi Stephen,

On 12/21/20 8:24 PM, Stephen Kitt wrote:
> Hi Alex,
>
> On Sat, 19 Dec 2020 15:00:00 +0100, "Alejandro Colomar (man-pages)"
> <alx.manpages@gmail.com> wrote:
>> On 12/18/20 5:58 PM, Stephen Kitt wrote:
> [...]
>>> +This program executes the command given on its command-line after
>>> +opening the files listed after the command,
>>> +and then using
>>
>> s/using/uses/
>
> It’s the same form as “opening”: “after opening ... and then using”. The
> overall sequence is “open”, “close_range”, “execve”.
>
> Regards,
>
> Stephen
>


Ahhh.  Then I think the comma is misleading.
What about the following?:


On 12/18/20 5:58 PM, Stephen Kitt wrote:
> +.PP
> +This program executes the command given on its command-line after
> +opening the files listed after the command,
> +and then using
> +.B close_range
> +to close them:

This program executes the command given on its command line,
after opening the files listed after the command
and then using *close_range()* to close them:


Thanks,

Alex

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/

Re: [PATCH v3] close_range.2: new page documenting close_range(2)

[Stephen Kitt]

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Hi Alex,

On Mon, 21 Dec 2020 20:33:06 +0100, "Alejandro Colomar (man-pages)"
<alx.manpages@gmail.com> wrote:
> On 12/21/20 8:24 PM, Stephen Kitt wrote:
> > On Sat, 19 Dec 2020 15:00:00 +0100, "Alejandro Colomar (man-pages)"
> > <alx.manpages@gmail.com> wrote:  
> >> On 12/18/20 5:58 PM, Stephen Kitt wrote:  
> > [...]  
> >>> +This program executes the command given on its command-line after
> >>> +opening the files listed after the command,
> >>> +and then using  
> >>
> >> s/using/uses/  
> >
> > It’s the same form as “opening”: “after opening ... and then using”. The
> > overall sequence is “open”, “close_range”, “execve”.
> 
> Ahhh.  Then I think the comma is misleading.
> What about the following?:
> 
> 
> On 12/18/20 5:58 PM, Stephen Kitt wrote:
> > +.PP
> > +This program executes the command given on its command-line after
> > +opening the files listed after the command,
> > +and then using
> > +.B close_range
> > +to close them:  
> 
> This program executes the command given on its command line,
> after opening the files listed after the command
> and then using *close_range()* to close them:

Yes, that works better.

I’ll follow up with a v5 with just that change.

Regards,

Stephen

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