On Mon, 2022-08-22 at 13:39 -0400, Mimi Zohar wrote: > On Mon, 2022-08-22 at 12:22 -0400, Jeff Layton wrote: > > On Mon, 2022-08-22 at 11:40 -0400, Mimi Zohar wrote: > > > On Mon, 2022-08-22 at 09:33 -0400, Jeff Layton wrote: > > > > Add an explicit paragraph codifying that atime updates due to reads > > > > should not be counted against the i_version counter. None of the > > > > existing subsystems that use the i_version want those counted, and > > > > there is an easy workaround for those that do. > > > > > > > > Cc: NeilBrown <neilb@xxxxxxx> > > > > Cc: Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> > > > > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > > > > Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@xxxxxxxxxxxxxxxxxxxxx/#t > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > > --- > > > > include/linux/iversion.h | 10 ++++++++-- > > > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/include/linux/iversion.h b/include/linux/iversion.h > > > > index 3bfebde5a1a6..da6cc1cc520a 100644 > > > > --- a/include/linux/iversion.h > > > > +++ b/include/linux/iversion.h > > > > @@ -9,8 +9,8 @@ > > > > * --------------------------- > > > > * The change attribute (i_version) is mandated by NFSv4 and is mostly for > > > > * knfsd, but is also used for other purposes (e.g. IMA). The i_version must > > > > - * appear different to observers if there was a change to the inode's data or > > > > - * metadata since it was last queried. > > > > + * appear different to observers if there was an explicit change to the inode's > > > > + * data or metadata since it was last queried. > > > > * > > > > * Observers see the i_version as a 64-bit number that never decreases. If it > > > > * remains the same since it was last checked, then nothing has changed in the > > > > @@ -18,6 +18,12 @@ > > > > * anything about the nature or magnitude of the changes from the value, only > > > > * that the inode has changed in some fashion. > > > > * > > > > + * Note that atime updates due to reads or similar activity do _not_ represent > > > > + * an explicit change to the inode. If the only change is to the atime and it > > > > > > Thanks, Jeff. The ext4 patch increments i_version on file metadata > > > changes. Could the wording here be more explicit to reflect changes > > > based on either inode data or metadata changes?b > > > > > > > > > > Thanks Mimi, > > > > Care to suggest some wording? > > > > The main issue we have is that ext4 and xfs both increment i_version on > > atime updates due to reads. I have patches in flight to fix those, but > > going forward, we want to ensure that i_version gets incremented on all > > changes _except_ for atime updates. > > > > The best wording we have at the moment is what Trond suggested, which is > > to classify the changes to the inode as "explicit" (someone or something > > made a deliberate change to the inode) and "implicit" (the change to the > > inode was due to activity such as reads that don't actually change > > anything). > > > > Is there a better way to describe this? > > "explicit change to the inode" probably implies both the inode file > data and metadata, but let's call it out by saying "an explicit change > to either the inode data or metadata". > > > > > > > + * wasn't set via utimes() or a similar mechanism, then i_version should not be > > > > + * incremented. If an observer cares about atime updates, it should plan to > > > > + * fetch and store them in conjunction with the i_version. > > > > + * > > > > * Not all filesystems properly implement the i_version counter. Subsystems that > > > > * want to use i_version field on an inode should first check whether the > > > > * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro). > > > > > > > > > > Thanks Mimi, Here's what I have now. I'll plan to send a v2 patch once others have had a chance to comment as well. -- Jeff diff --git a/include/linux/iversion.h b/include/linux/iversion.h index 3bfebde5a1a6..524abd372100 100644 --- a/include/linux/iversion.h +++ b/include/linux/iversion.h @@ -9,8 +9,8 @@ * --------------------------- * The change attribute (i_version) is mandated by NFSv4 and is mostly for * knfsd, but is also used for other purposes (e.g. IMA). The i_version must - * appear different to observers if there was a change to the inode's data or - * metadata since it was last queried. + * appear different to observers if there was an explicit change to the inode's + * data or metadata since it was last queried. * * Observers see the i_version as a 64-bit number that never decreases. If it * remains the same since it was last checked, then nothing has changed in the @@ -18,6 +18,13 @@ * anything about the nature or magnitude of the changes from the value, only * that the inode has changed in some fashion. * + * Note that atime updates due to reads or similar activity do not represent + * an explicit change to the inode data or metadata. If the only change is to + * the atime and it wasn't set via utimes() or a similar mechanism, then + * i_version should not be incremented. If an observer cares about atime + * updates, it should plan to fetch and store them in conjunction with the + * i_version. + * * Not all filesystems properly implement the i_version counter. Subsystems that * want to use i_version field on an inode should first check whether the * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro). -- Jeff Layton <jlayton@xxxxxxxxxx>
