| Message ID | 20220930111840.10695-3-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfs/nfsd: clean up handling of i_version counter | expand |
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@verbum.org> > Cc: NeilBrown <neilb@suse.de> > Cc: Trond Myklebust <trondmy@hammerspace.com> > Cc: Dave Chinner <david@fromorbit.com> > Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t > Signed-off-by: Jeff Layton <jlayton@kernel.org> > --- > 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@suse.de> 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 > >
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@verbum.org> > > Cc: NeilBrown <neilb@suse.de> > > Cc: Trond Myklebust <trondmy@hammerspace.com> > > Cc: Dave Chinner <david@fromorbit.com> > > Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > --- > > 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@suse.de> > > 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 > > > >
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. * * 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
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@verbum.org> Cc: NeilBrown <neilb@suse.de> Cc: Trond Myklebust <trondmy@hammerspace.com> Cc: Dave Chinner <david@fromorbit.com> Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t Signed-off-by: Jeff Layton <jlayton@kernel.org> --- include/linux/iversion.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)