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fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.\" Copyright (c) 2021 The FreeBSD Foundation, Inc.
.\"
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.\" Copyright (c) 1996
.\" Mike Pritchard <mpp@FreeBSD.org>. All rights reserved.
.\"
.\" Copyright (c) 1992, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\" All rights reserved.
.\"
.\" This code is derived from software donated to Berkeley by
.\" Jan-Simon Pendry.
.\"
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.\" Parts of this documentation was written by
.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
.\" from the FreeBSD Foundation.
.\"
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
multiple: Remove 3rd clause from BSD license where approved by the regents and renumber. This patch skips files in contrib/ and crypto/ Acked by: imp Discussed with: emaste
2014-03-14 03:07:51 +00:00
.\" 3. Neither the name of the University nor the names of its contributors
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
add missing cvs Id lines.
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.\"
$Id$ -> $FreeBSD$
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.\" $FreeBSD$
add missing cvs Id lines.
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.\"
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.Dd May 17, 2021
Rename (after a repo-copy) some mount(8) programs: mount_fdesc -> mount_fdescfs mount_null -> mount_nullfs mount_portal -> mount_portalfs mount_umap -> mount_umapfs mount_union -> mount_unionfs
2001-05-23 14:58:19 +00:00
.Dt FDESCFS 5
.Os
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Sh NAME
Rename (after a repo-copy) some mount(8) programs: mount_fdesc -> mount_fdescfs mount_null -> mount_nullfs mount_portal -> mount_portalfs mount_umap -> mount_umapfs mount_union -> mount_unionfs
2001-05-23 14:58:19 +00:00
.Nm fdescfs
Uniformly refer to a file system as "file system". Approved by: re
2002-12-12 17:26:04 +00:00
.Nd file-descriptor file system
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Sh SYNOPSIS
Deal with unsafe tab characters.
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.Bd -literal
Rename (after a repo-copy) some mount(8) programs: mount_fdesc -> mount_fdescfs mount_null -> mount_nullfs mount_portal -> mount_portalfs mount_umap -> mount_umapfs mount_union -> mount_unionfs
2001-05-23 14:58:19 +00:00
fdescfs /dev/fd fdescfs rw 0 0
Deal with unsafe tab characters.
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.Ed
Add fdesc(5) to document the file-descriptor file system.
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.Sh DESCRIPTION
Uniformly refer to a file system as "file system". Approved by: re
2002-12-12 17:26:04 +00:00
The file-descriptor file system, or
mdoc(7) police: use the new features of the Nm macro.
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.Nm ,
Add fdesc(5) to document the file-descriptor file system.
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provides access to the per-process file descriptor
Uniformly refer to a file system as "file system". Approved by: re
2002-12-12 17:26:04 +00:00
namespace in the global file system namespace.
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
The conventional mount point is
Document the `new' fdesc--now that it belongs only on /dev/fd, remove all non-/dev/fd related documentation (such as that for stdin, stdout, tty). Update the fstab line to refer to /dev/fd instead of /dev.
2000-05-11 22:20:23 +00:00
.Pa /dev/fd .
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Pp
Uniformly refer to a file system as "file system". Approved by: re
2002-12-12 17:26:04 +00:00
The file system's contents
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
appear as a list of numbered files
which correspond to the open files of the process reading the
directory.
The files
.Pa /dev/fd/0
through
.Pa /dev/fd/#
refer to file descriptors which can be accessed through the file
system.
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.Pp
The following mount options can be used when mounting
.Nm
filesystem:
.Bl -tag -width linrdlnk
.It Cm nodup
For file descriptors referencing vnodes, instead of the
.Xr dup 2
semantic described above, implement re-opening of the referenced vnode.
See below for more details.
.It Cm linrdlnk
Report the type of the
.Nm
vnode as
.Dv VLNK
instead of
.Fx
traditional
.Dv VCHR .
For
.Xr linux 4
ABI compatibility mount
.Nm
volume with the
.Cm linrdlnk
option.
.El
.Pp
For
.Nm
mounted without the
.Cm nodup
mount option,
if the file descriptor is open and the mode the file is being opened
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
with is a subset of the mode of the existing descriptor, the call:
.Bd -literal -offset indent
fd = open("/dev/fd/0", mode);
.Ed
.Pp
and the call:
.Bd -literal -offset indent
fd = fcntl(0, F_DUPFD, 0);
.Ed
.Pp
are equivalent.
Flags to the
.Xr open 2
call other than
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
.Dv O_RDONLY ,
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Dv O_WRONLY
and
.Dv O_RDWR
are ignored.
Note that devfs(5) and fdescfs(5) both create /dev/fd file descriptors. PR: 144534 Submitted by: Matthew Seaman <m.seaman at infracaninophile co uk> Patch by: Matthew Seaman, keramida Approved by: keramida (mentor) MFC after: 1 week
2010-09-18 19:23:14 +00:00
.Pp
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
For
.Nm
mounted with the
.Cm nodup
option, and file descriptor referencing a vnode, the call:
.Bd -literal -offset indent
fd = open("/dev/fd/0", mode);
.Ed
.Pp
reopens the referenced vnode with the specified
.Fa mode .
In other words, the
.Fn open
call above is equivalent to
.Bd -literal -offset indent
fd = openat(0, "", O_EMPTY_PATH, mode);
.Ed
.Pp
In particular, if the file descriptor was opened with the
.Dv O_PATH
flag, then either
.Dv O_EMPTY_PATH
or
.Fn open
over
.Nm
mount with
.Cm nodup
option allows one to convert it to a regularly opened file,
assuming that the current permissions allow the requested
.Fa mode .
.Pp
Note that devfs(5) and fdescfs(5) both create /dev/fd file descriptors. PR: 144534 Submitted by: Matthew Seaman <m.seaman at infracaninophile co uk> Patch by: Matthew Seaman, keramida Approved by: keramida (mentor) MFC after: 1 week
2010-09-18 19:23:14 +00:00
.Em "Note:"
.Pa /dev/fd/0 ,
.Pa /dev/fd/1
and
.Pa /dev/fd/2
files are created by default when devfs alone is mounted.
.Nm
creates entries for all file descriptors opened by the process.
mdoc: move remaining sections into consistent order This pertains mostly to FILES, HISTORY, EXIT STATUS and AUTHORS sections. Found by: mdocml lint run Reviewed by: ru
2010-05-13 12:08:11 +00:00
.Sh FILES
.Bl -tag -width /dev/stderr -compact
.It Pa /dev/fd/#
.El
Change reference from mount_devfs(8) to mount(8), and add an example. Remove reference to mount_fdescfs(8), since mount(8) calls nmount() directly to mount an fdescfs filesystem, instead of forking an external mount_fdescfs program.
2006-11-21 04:56:50 +00:00
.Sh EXAMPLES
Remove trailing whitespace per mdoc lint warning Disussed with: gavin No objection from: doc Approved by: joel MFC after: 3 days
2012-03-29 05:02:12 +00:00
To mount a
Change reference from mount_devfs(8) to mount(8), and add an example. Remove reference to mount_fdescfs(8), since mount(8) calls nmount() directly to mount an fdescfs filesystem, instead of forking an external mount_fdescfs program.
2006-11-21 04:56:50 +00:00
.Nm
volume located on
.Pa /dev/fd :
.Pp
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.Dl "mount -t fdescfs none /dev/fd"
Implement proper Linux /dev/fd and /proc/self/fd behavior by adding Linux specific things to the native fdescfs file system. Unlike FreeBSD, the Linux fdescfs is a directory containing a symbolic links to the actual files, which the process has open. A readlink(2) call on this file returns a full path in case of regular file or a string in a special format (type:[inode], anon_inode:<file-type>, etc..). As well as in a FreeBSD, opening the file in the Linux fdescfs directory is equivalent to duplicating the corresponding file descriptor. Here we have mutually exclusive requirements: - in case of readlink(2) call fdescfs lookup() method should return VLNK vnode otherwise our kern_readlink() fail with EINVAL error; - in the other calls fdescfs lookup() method should return non VLNK vnode. For what new vnode v_flag VV_READLINK was added, which is set if fdescfs has beed mounted with linrdlnk option an modified kern_readlinkat() to properly handle it. For now For Linux ABI compatibility mount fdescfs volume with linrdlnk option: mount -t fdescfs -o linrdlnk null /compat/linux/dev/fd Reviewed by: kib@ MFC after: 1 week Relnotes: yes
2017-08-01 03:40:19 +00:00
.Pp
For
.Xr linux 4
ABI compatibility:
.Pp
fdescfs: add an option to return underlying file vnode on lookup The 'nodup' option forces fdescfs to return real vnode behind file descriptor instead of the fdescfs fd vnode, on lookup. The end result is that e.g. stat("/dev/fd/3") returns the stat data for the underlying vnode, if any. Similarly, fchdir(2) works in the expected way. For open(2), if applied over file descriptor opened with O_PATH, it effectively re-open that vnode into normal file descriptor which has the specified access mode, assuming the current vnode permissions allow it. If the file descriptor does not reference vnode, the behavior is unchanged. This is done by a mount option, because permission check on open(2) breaks established fdescfs open semantic of dup(2)-ing the descriptor. So it is not suitable for /dev/fd mount. Tested by: Andrew Walker <awalker@ixsystems.com> Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D30140
2021-05-05 22:53:20 +00:00
.Dl "mount -t fdescfs -o linrdlnk none /compat/linux/dev/fd"
.Pp
For substitute of
.Dv O_EMPTY_PATH
flag use:
.Pp
.Dl "mount -t fdescfs -o nodup none /dev/fdpath"
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Sh SEE ALSO
Note that devfs(5) and fdescfs(5) both create /dev/fd file descriptors. PR: 144534 Submitted by: Matthew Seaman <m.seaman at infracaninophile co uk> Patch by: Matthew Seaman, keramida Approved by: keramida (mentor) MFC after: 1 week
2010-09-18 19:23:14 +00:00
.Xr devfs 5 ,
Change reference from mount_devfs(8) to mount(8), and add an example. Remove reference to mount_fdescfs(8), since mount(8) calls nmount() directly to mount an fdescfs filesystem, instead of forking an external mount_fdescfs program.
2006-11-21 04:56:50 +00:00
.Xr mount 8
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Sh HISTORY
The
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
.Nm
Uniformly refer to a file system as "file system". Approved by: re
2002-12-12 17:26:04 +00:00
file system first appeared in
Various man page cleanup: - Sort xrefs - FreeBSD.ORG -> FreeBSD.org - Be consistent with section names as outlined in mdoc(7). - Other misc mdoc cleanup. PR: doc/13144 Submitted by: Alexey M. Zelkin <phantom@cris.net>
1999-08-15 10:48:36 +00:00
.Bx 4.4 .
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
The
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Nm
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
manual page first appeared in
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Fx 2.2 .
.Sh AUTHOR -> .Sh AUTHORS according to mdoc specs. Use .An/.Aq.
1998-03-12 07:31:21 +00:00
.Sh AUTHORS
mdoc(7) police: do not split author names in the AUTHORS section.
2000-11-22 09:35:58 +00:00
.An -nosplit
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
The
Add fdesc(5) to document the file-descriptor file system.
1996-12-14 22:14:55 +00:00
.Nm
.Sh AUTHOR -> .Sh AUTHORS according to mdoc specs. Use .An/.Aq.
1998-03-12 07:31:21 +00:00
manual page was written by
use .Mt to mark up email addresses consistently (part6) PR: 191174 Submitted by: Franco Fichtner <franco at lastsummer.de>
2014-06-23 08:27:27 +00:00
.An Mike Pritchard Aq Mt mpp@FreeBSD.org ,
Removed whitespace at end-of-line; no content changes. I simply did cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//' BTW, what editors are the culprits? I'm using vim and it shows me whitespace at EOL in troff files with a thick blue block... Reviewed by: Silence from cvs diff -b MFC after: 7 days
2001-07-14 19:41:16 +00:00
and was based on the
.Sh AUTHOR -> .Sh AUTHORS according to mdoc specs. Use .An/.Aq.
1998-03-12 07:31:21 +00:00
manual page written by
.An Jan-Simon Pendry .
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