Hello. On úterý 14. října 2025 1:32:29, středoevropský letní čas Darrick J. Wong wrote: > From: Darrick J. Wong > > Apparently we can never deprecate mount options in this project, because > it will invariably turn out that some foolish userspace depends on some > behavior and break. From Oleksandr Natalenko: > > > In v6.18, the attr2 XFS mount option is removed. This may silently > > break system boot if the attr2 option is still present in /etc/fstab > > for rootfs. > > > > Consider Arch Linux that is being set up from scratch with / being > > formatted as XFS. The genfstab command that is used to generate > > /etc/fstab produces something like this by default: > > > > /dev/sda2 on / type xfs (rw,relatime,attr2,discard,inode64,logbufs=8,logbsize=32k,noquota) > > > > Once the system is set up and rebooted, there's no deprecation warning > > seen in the kernel log: > > > > # cat /proc/cmdline > > root=UUID=77b42de2-397e-47ee-a1ef-4dfd430e47e9 rootflags=discard rd.luks.options=discard quiet > > > > # dmesg | grep -i xfs > > [ 2.409818] SGI XFS with ACLs, security attributes, realtime, scrub, repair, quota, no debug enabled > > [ 2.415341] XFS (sda2): Mounting V5 Filesystem 77b42de2-397e-47ee-a1ef-4dfd430e47e9 > > [ 2.442546] XFS (sda2): Ending clean mount > > > > Although as per the deprecation intention, it should be there. > > > > Vlastimil (in Cc) suggests this is because xfs_fs_warn_deprecated() > > doesn't produce any warning by design if the XFS FS is set to be > > rootfs and gets remounted read-write during boot. This imposes two > > problems: > > > > 1) a user doesn't see the deprecation warning; and > > 2) with v6.18 kernel, the read-write remount fails because of unknown > > attr2 option rendering system unusable: > > > > systemd[1]: Switching root. > > systemd-remount-fs[225]: /usr/bin/mount for / exited with exit status 32. > > > > # mount -o rw / > > mount: /: fsconfig() failed: xfs: Unknown parameter 'attr2'. > > > > Thorsten (in Cc) suggested reporting this as a user-visible regression. > > > > From my PoV, although the deprecation is in place for 5 years already, > > it may not be visible enough as the warning is not emitted for rootfs. > > Considering the amount of systems set up with XFS on /, this may > > impose a mass problem for users. > > > > Vlastimil suggested making attr2 option a complete noop instead of > > removing it. > > IOWs, the initrd mounts the root fs with (I assume) no mount options, > and mount -a remounts with whatever options are in fstab. However, > XFS doesn't complain about deprecated mount options during a remount, so > technically speaking we were not warning all users in all combinations > that they were heading for a cliff. > > Gotcha!! > > Now, how did 'attr2' get slurped up on so many systems? The old code > would put that in /proc/mounts if the filesystem happened to be in attr2 > mode, even if user hadn't mounted with any such option. IOWs, this is > because someone thought it would be a good idea to advertise system > state via /proc/mounts. > > The easy way to fix this is to reintroduce the four mount options but > map them to a no-op option that ignores them, and hope that nobody's > depending on attr2 to appear in /proc/mounts. (Hint: use the fsgeometry > ioctl). > > Lessons learned: > > 1. Don't expose system state via /proc/mounts; the only strings that > ought to be there are options *explicitly* provided by the user. > 2. Never tidy, it's not worth the stress and irritation. > > Reported-by: oleksandr@natalenko.name > Reported-by: vbabka@suse.cz > Cc: # v6.18-rc1 > Fixes: b9a176e54162f8 ("xfs: remove deprecated mount options") > Signed-off-by: "Darrick J. Wong" > --- > fs/xfs/xfs_super.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > index e85a156dc17d16..e1df41991fccc3 100644 > --- a/fs/xfs/xfs_super.c > +++ b/fs/xfs/xfs_super.c > @@ -102,7 +102,7 @@ static const struct constant_table dax_param_enums[] = { > * Table driven mount option parser. > */ > enum { > - Opt_logbufs, Opt_logbsize, Opt_logdev, Opt_rtdev, > + Opt_quietlyignore, Opt_logbufs, Opt_logbsize, Opt_logdev, Opt_rtdev, > Opt_wsync, Opt_noalign, Opt_swalloc, Opt_sunit, Opt_swidth, Opt_nouuid, > Opt_grpid, Opt_nogrpid, Opt_bsdgroups, Opt_sysvgroups, > Opt_allocsize, Opt_norecovery, Opt_inode64, Opt_inode32, > @@ -115,6 +115,14 @@ enum { > }; > > static const struct fs_parameter_spec xfs_fs_parameters[] = { > + /* > + * These mount options were advertised in /proc/mounts even if the > + * filesystem had not been mounted with that option. Quietly ignore > + * them to avoid breaking scripts that captured /proc/mounts. > + */ > + fsparam_flag("attr", Opt_quietlyignore), Should have been "attr2" here I suppose. Thanks. > + fsparam_flag("noattr2", Opt_quietlyignore), > + > fsparam_u32("logbufs", Opt_logbufs), > fsparam_string("logbsize", Opt_logbsize), > fsparam_string("logdev", Opt_logdev), > @@ -1408,6 +1416,8 @@ xfs_fs_parse_param( > return opt; > > switch (opt) { > + case Opt_quietlyignore: > + return 0; > case Opt_logbufs: > parsing_mp->m_logbufs = result.uint_32; > return 0; > @@ -1528,7 +1538,6 @@ xfs_fs_parse_param( > xfs_mount_set_dax_mode(parsing_mp, result.uint_32); > return 0; > #endif > - /* Following mount options will be removed in September 2025 */ > case Opt_max_open_zones: > parsing_mp->m_max_open_zones = result.uint_32; > return 0; > -- Oleksandr Natalenko, MSE