Re: [PATCH v4 6/9] xfs: switch to multigrain timestamps

Jeff Layton
2024-07-08T18:51:10Z

On Mon, 2024-07-08 at 11:47 -0700, Darrick J. Wong wrote:
> On Mon, Jul 08, 2024 at 11:53:39AM -0400, Jeff Layton wrote:
> > Enable multigrain timestamps, which should ensure that there is an
> > apparent change to the timestamp whenever it has been written after
> > being actively observed via getattr.
> >
> > Also, anytime the mtime changes, the ctime must also change, and those
> > are now the only two options for xfs_trans_ichgtime. Have that function
> > unconditionally bump the ctime, and ASSERT that XFS_ICHGTIME_CHG is
> > always set.
> >
> > Finally, stop setting STATX_CHANGE_COOKIE in getattr, since the ctime
> > should give us better semantics now.
> >
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/xfs/libxfs/xfs_trans_inode.c | 6 +++---
> > fs/xfs/xfs_iops.c | 10 +++-------
> > fs/xfs/xfs_super.c | 2 +-
> > 3 files changed, 7 insertions(+), 11 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> > index 69fc5b981352..1f3639bbf5f0 100644
> > --- a/fs/xfs/libxfs/xfs_trans_inode.c
> > +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> > @@ -62,12 +62,12 @@ xfs_trans_ichgtime(
> > ASSERT(tp);
> > xfs_assert_ilocked(ip, XFS_ILOCK_EXCL);
> >
> > - tv = current_time(inode);
> > + /* If the mtime changes, then ctime must also change */
> > + ASSERT(flags & XFS_ICHGTIME_CHG);
> >
> > + tv = inode_set_ctime_current(inode);
> > if (flags & XFS_ICHGTIME_MOD)
> > inode_set_mtime_to_ts(inode, tv);
> > - if (flags & XFS_ICHGTIME_CHG)
> > - inode_set_ctime_to_ts(inode, tv);
> > if (flags & XFS_ICHGTIME_CREATE)
> > ip->i_crtime = tv;
> > }
> > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> > index a00dcbc77e12..d25872f818fa 100644
> > --- a/fs/xfs/xfs_iops.c
> > +++ b/fs/xfs/xfs_iops.c
> > @@ -592,8 +592,9 @@ xfs_vn_getattr(
> > stat->gid = vfsgid_into_kgid(vfsgid);
> > stat->ino = ip->i_ino;
> > stat->atime = inode_get_atime(inode);
> > - stat->mtime = inode_get_mtime(inode);
> > - stat->ctime = inode_get_ctime(inode);
> > +
> > + fill_mg_cmtime(stat, request_mask, inode);
>
> Sooo... for setting up a commit-range operation[1], XFS_IOC_START_COMMIT
> could populate its freshness data by calling:
>
> struct kstat dummy;
>
> fill_mg_ctime(&dummy, STATX_CTIME | STATX_MTIME, inode);
>
> and then using dummy.[cm]time to populate the freshness data that it
> gives to userspace, right? Having set QUERIED, a write to the file
> immediately afterwards will cause a (tiny) increase in ctime_nsec which
> will cause the XFS_IOC_COMMIT_RANGE to reject the commit[2]. Right?
>

Yes. Once you call fill_mg_ctime, the first write after that point
should cause the kernel to ensure that there is a distinct change in
the ctime.

IOW, I think this should alleviate the concerns I had before with using
timestamps with the XFS_IOC_COMMIT_RANGE interface.

> --D
>
> [1] https://lore.kernel.org/linux-xfs/20240227174649.GL6184@frogsfrogsfrogs/
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=atomic-file-commits&id=0520d89c2698874c1f56ddf52ec4b8a3595baa14
>
> > +
> > stat->blocks = XFS_FSB_TO_BB(mp, ip->i_nblocks + ip->i_delayed_blks);
> >
> > if (xfs_has_v3inodes(mp)) {
> > @@ -603,11 +604,6 @@ xfs_vn_getattr(
> > }
> > }
> >
> > - if ((request_mask & STATX_CHANGE_COOKIE) && IS_I_VERSION(inode)) {
> > - stat->change_cookie = inode_query_iversion(inode);
> > - stat->result_mask |= STATX_CHANGE_COOKIE;
> > - }
> > -
> > /*
> > * Note: If you add another clause to set an attribute flag, please
> > * update attributes_mask below.
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index 27e9f749c4c7..210481b03fdb 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -2052,7 +2052,7 @@ static struct file_system_type xfs_fs_type = {
> > .init_fs_context = xfs_init_fs_context,
> > .parameters = xfs_fs_parameters,
> > .kill_sb = xfs_kill_sb,
> > - .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
> > + .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME,
> > };
> > MODULE_ALIAS_FS("xfs");
> >
> >
> > --
> > 2.45.2
> >
> >

--
Jeff Layton <jlayton@kernel.org>