Date: Fri, 11 Jun 2021 00:48:01 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 043f20498526 - stable/13 - fdescfs: add an option to return underlying file vnode on lookup Message-ID: <202106110048.15B0m1w9047989@gitrepo.freebsd.org>
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The branch stable/13 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=043f204985261d6daae69538c4609b3e143ee444 commit 043f204985261d6daae69538c4609b3e143ee444 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-05-05 22:53:20 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2021-06-11 00:33:48 +0000 fdescfs: add an option to return underlying file vnode on lookup (cherry picked from commit f9b1e711f0d8c27f2d29e7a8e6276947d37a6a22) --- 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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