On Tue, 2022-10-04 at 10:10 +1100, NeilBrown wrote: > On Fri, 30 Sep 2022, Jeff Layton wrote: > > The i_version field in the kernel has had different semantics over > > the decades, but NFSv4 has certain expectations. Update the comments > > in iversion.h to describe when the i_version must change. > > > > Cc: Colin Walters <walters@xxxxxxxxxx> > > 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 6755d8b4f20b..9925cac1fa94 100644 > > --- a/include/linux/iversion.h > > +++ b/include/linux/iversion.h > > @@ -9,8 +9,14 @@ > > * --------------------------- > > * 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 larger to observers if there was an explicit change to the inode's > > + * data or metadata since it was last queried. > > + * > > + * An explicit change is one that would ordinarily result in a change to the > > + * inode status change time (aka ctime). i_version must appear to change, even > > + * if the ctime does not (since the whole point is to avoid missing updates due > > + * to timestamp granularity). If POSIX mandates that the ctime must change due > > + * to an operation, then the i_version counter must be incremented as well. > > POSIX doesn't (that I can see) describe when the ctime changes w.r.t > when the file changes. For i_version we do want to specify that > i_version change is not visible before the file change is visible. > So this goes beyond the POSIX mandate. I might be worth making that > explicit. > But this patch is nonetheless an improvement, so: > > Reviewed-by: NeilBrown <neilb@xxxxxxx> > > Thanks, Now that we're looking at setting the ctime and i_version separately, I'll plan to add something that makes this explict. > > * > > * 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 > > -- > > 2.37.3 > > > > -- Jeff Layton <jlayton@xxxxxxxxxx>
