On Tue, Aug 16, 2022 at 09:17:36AM -0400, Jeff Layton wrote:
> The i_version in xfs_trans_log_inode is bumped for any inode update,
> including atime-only updates due to reads. We don't want to record those
> in the i_version, as they don't represent "real" changes. Remove that
> callsite.
>
> In xfs_vn_update_time, if S_VERSION is flagged, then attempt to bump the
> i_version and turn on XFS_ILOG_CORE if it happens. In
> xfs_trans_ichgtime, update the i_version if the mtime or ctime are being
> updated.
What about operations that don't touch the mtime but change the file
metadata anyway? There are a few of those, like the blockgc garbage
collector, deduperange, and the defrag tool.
Zooming out a bit -- what does i_version signal, concretely? I thought
it was used by nfs (and maybe ceph?) to signal to clients that the file
on the server has moved on, and the client needs to invalidate its
caches. I thought afs had a similar generation counter, though it's
only used to cache file data, not metadata? Does an i_version change
cause all of them to invalidate caches, or is there more behavior I
don't know about?
Does that mean that we should bump i_version for any file data or
attribute that could be queried or observed by userspace? In which case
I suppose this change is still correct, even if it relaxes i_version
updates from "any change to the inode whatsoever" to "any change that
would bump mtime". Unless FIEMAP is part of "attributes observed by
userspace".
(The other downside I can see is that now we have to remember to bump
timestamps for every new file operation we add, unlike the current code
which is centrally located in xfs_trans_log_inode.)
--D
> Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_trans_inode.c | 17 +++--------------
> fs/xfs/xfs_iops.c | 4 ++++
> 2 files changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> index 8b5547073379..78bf7f491462 100644
> --- a/fs/xfs/libxfs/xfs_trans_inode.c
> +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> @@ -71,6 +71,8 @@ xfs_trans_ichgtime(
> inode->i_ctime = tv;
> if (flags & XFS_ICHGTIME_CREATE)
> ip->i_crtime = tv;
> + if (flags & (XFS_ICHGTIME_MOD|XFS_ICHGTIME_CHG))
> + inode_inc_iversion(inode);
> }
>
> /*
> @@ -116,20 +118,7 @@ xfs_trans_log_inode(
> spin_unlock(&inode->i_lock);
> }
>
> - /*
> - * First time we log the inode in a transaction, bump the inode change
> - * counter if it is configured for this to occur. While we have the
> - * inode locked exclusively for metadata modification, we can usually
> - * avoid setting XFS_ILOG_CORE if no one has queried the value since
> - * the last time it was incremented. If we have XFS_ILOG_CORE already
> - * set however, then go ahead and bump the i_version counter
> - * unconditionally.
> - */
> - if (!test_and_set_bit(XFS_LI_DIRTY, &iip->ili_item.li_flags)) {
> - if (IS_I_VERSION(inode) &&
> - inode_maybe_inc_iversion(inode, flags & XFS_ILOG_CORE))
> - iversion_flags = XFS_ILOG_CORE;
> - }
> + set_bit(XFS_LI_DIRTY, &iip->ili_item.li_flags);
>
> /*
> * If we're updating the inode core or the timestamps and it's possible
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 45518b8c613c..162e044c7f56 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -718,6 +718,7 @@ xfs_setattr_nonsize(
> }
>
> setattr_copy(mnt_userns, inode, iattr);
> + inode_inc_iversion(inode);
> xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
>
> XFS_STATS_INC(mp, xs_ig_attrchg);
> @@ -943,6 +944,7 @@ xfs_setattr_size(
>
> ASSERT(!(iattr->ia_valid & (ATTR_UID | ATTR_GID)));
> setattr_copy(mnt_userns, inode, iattr);
> + inode_inc_iversion(inode);
> xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
>
> XFS_STATS_INC(mp, xs_ig_attrchg);
> @@ -1047,6 +1049,8 @@ xfs_vn_update_time(
> inode->i_mtime = *now;
> if (flags & S_ATIME)
> inode->i_atime = *now;
> + if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
> + log_flags |= XFS_ILOG_CORE;
>
> xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
> xfs_trans_log_inode(tp, ip, log_flags);
> --
> 2.37.2
>
