Date: Fri, 4 Jun 2021 00:30:28 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: f9b1e711f0d8 - main - fdescfs: add an option to return underlying file vnode on lookup Message-ID: <202106040030.1540USg0002418@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=f9b1e711f0d8c27f2d29e7a8e6276947d37a6a22 commit f9b1e711f0d8c27f2d29e7a8e6276947d37a6a22 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-05-05 22:53:20 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2021-06-04 00:30:12 +0000 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 --- share/man/man5/fdescfs.5 | 94 +++++++++++++++++++++++++++++++++++++------ sys/fs/fdescfs/fdesc.h | 1 + sys/fs/fdescfs/fdesc_vfsops.c | 2 + sys/fs/fdescfs/fdesc_vnops.c | 12 +++++- 4 files changed, 95 insertions(+), 14 deletions(-) diff --git a/share/man/man5/fdescfs.5 b/share/man/man5/fdescfs.5 index 3f16104c0ac8..f2abda2bb4c2 100644 --- a/share/man/man5/fdescfs.5 +++ b/share/man/man5/fdescfs.5 @@ -1,3 +1,5 @@ +.\" Copyright (c) 2021 The FreeBSD Foundation, Inc. +.\" .\" Copyright (c) 1996 .\" Mike Pritchard <mpp@FreeBSD.org>. All rights reserved. .\" @@ -8,6 +10,10 @@ .\" This code is derived from software donated to Berkeley by .\" Jan-Simon Pendry. .\" +.\" Parts of this documentation was written by +.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship +.\" from the FreeBSD Foundation. +.\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: @@ -34,7 +40,7 @@ .\" .\" $FreeBSD$ .\" -.Dd August 1, 2017 +.Dd May 17, 2021 .Dt FDESCFS 5 .Os .Sh NAME @@ -62,7 +68,40 @@ through .Pa /dev/fd/# refer to file descriptors which can be accessed through the file system. -If the file descriptor is open and the mode the file is being opened +.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 with is a subset of the mode of the existing descriptor, the call: .Bd -literal -offset indent fd = open("/dev/fd/0", mode); @@ -74,7 +113,6 @@ fd = fcntl(0, F_DUPFD, 0); .Ed .Pp are equivalent. -.Pp Flags to the .Xr open 2 call other than @@ -84,6 +122,38 @@ and .Dv O_RDWR are ignored. .Pp +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 .Em "Note:" .Pa /dev/fd/0 , .Pa /dev/fd/1 @@ -92,14 +162,6 @@ and files are created by default when devfs alone is mounted. .Nm creates entries for all file descriptors opened by the process. -.Pp -For -.Xr linux 4 -ABI compatibility mount -.Nm -volume with -.Cm linrdlnk -option. .Sh FILES .Bl -tag -width /dev/stderr -compact .It Pa /dev/fd/# @@ -110,13 +172,19 @@ To mount a volume located on .Pa /dev/fd : .Pp -.Dl "mount -t fdescfs null /dev/fd" +.Dl "mount -t fdescfs none /dev/fd" .Pp For .Xr linux 4 ABI compatibility: .Pp -.Dl "mount -t fdescfs -o linrdlnk null /compat/linux/dev/fd" +.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" .Sh SEE ALSO .Xr devfs 5 , .Xr mount 8 diff --git a/sys/fs/fdescfs/fdesc.h b/sys/fs/fdescfs/fdesc.h index b578b7309130..94682f42cdb3 100644 --- a/sys/fs/fdescfs/fdesc.h +++ b/sys/fs/fdescfs/fdesc.h @@ -42,6 +42,7 @@ /* Private mount flags for fdescfs. */ #define FMNT_UNMOUNTF 0x01 #define FMNT_LINRDLNKF 0x02 +#define FMNT_NODUP 0x04 struct fdescmount { struct vnode *f_root; /* Root node */ diff --git a/sys/fs/fdescfs/fdesc_vfsops.c b/sys/fs/fdescfs/fdesc_vfsops.c index 64f8d28bdcfd..9d8fdda47cbf 100644 --- a/sys/fs/fdescfs/fdesc_vfsops.c +++ b/sys/fs/fdescfs/fdesc_vfsops.c @@ -101,6 +101,8 @@ fdesc_mount(struct mount *mp) fmp->flags = 0; if (vfs_getopt(mp->mnt_optnew, "linrdlnk", NULL, NULL) == 0) fmp->flags |= FMNT_LINRDLNKF; + if (vfs_getopt(mp->mnt_optnew, "nodup", NULL, NULL) == 0) + fmp->flags |= FMNT_NODUP; error = fdesc_allocvp(Froot, -1, FD_ROOT, mp, &rvp); if (error) { free(fmp, M_FDESCMNT); diff --git a/sys/fs/fdescfs/fdesc_vnops.c b/sys/fs/fdescfs/fdesc_vnops.c index 1271b50e6e94..c5a7b86f1de5 100644 --- a/sys/fs/fdescfs/fdesc_vnops.c +++ b/sys/fs/fdescfs/fdesc_vnops.c @@ -264,10 +264,20 @@ fdesc_get_ino_alloc(struct mount *mp, void *arg, int lkflags, struct vnode **rvp) { struct fdesc_get_ino_args *a; + struct fdescmount *fdm; + struct vnode *vp; int error; a = arg; - error = fdesc_allocvp(a->ftype, a->fd_fd, a->ix, mp, rvp); + fdm = VFSTOFDESC(mp); + if ((fdm->flags & FMNT_NODUP) != 0 && a->fp->f_type == DTYPE_VNODE) { + vp = a->fp->f_vnode; + vget(vp, lkflags | LK_RETRY); + *rvp = vp; + error = 0; + } else { + error = fdesc_allocvp(a->ftype, a->fd_fd, a->ix, mp, rvp); + } fdrop(a->fp, a->td); return (error); }
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