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, NeilBrown > * > * 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 > >
