On Mon, Jul 3, 2023 at 9:14 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> On Wed, Jun 21, 2023 at 01:18:26PM +0200, Alexander Larsson wrote:
> > Historically overlay.metacopy was a zero-size xattr, and it's
> > existence marked a metacopy file. This change adds a versioned header
> > with a flag field, a length and a digest. The initial use-case of this
> > will be for validating a fs-verity digest, but the flags field could
> > also be used later for other new features.
> >
> > ovl_check_metacopy_xattr() now returns the size of the xattr,
> > emulating a size of OVL_METACOPY_MIN_SIZE for empty xattrs to
> > distinguish it from the no-xattr case.
> >
> > Signed-off-by: Alexander Larsson <alexl@xxxxxxxxxx>
> > ---
> > fs/overlayfs/namei.c | 10 +++++-----
> > fs/overlayfs/overlayfs.h | 24 +++++++++++++++++++++++-
> > fs/overlayfs/util.c | 37 +++++++++++++++++++++++++++++++++----
> > 3 files changed, 61 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> > index 57adf911735f..3dd480253710 100644
> > --- a/fs/overlayfs/namei.c
> > +++ b/fs/overlayfs/namei.c
> > @@ -25,7 +25,7 @@ struct ovl_lookup_data {
> > bool stop;
> > bool last;
> > char *redirect;
> > - bool metacopy;
> > + int metacopy;
>
> Should this be called 'metacopy_size' now?
Honestly I don't know. That would change a lot of locations that still
use this as "essentially" a boolean (i.e. != 0 means "has metacopy"),
and ity would make that code less compact. I guess this is up to Amir
and Miklos. Surely we could add a comment in the struct definition
though.
> > - err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path);
> > + err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path, NULL);
> > if (err < 0)
> > goto out_err;
>
> This part is confusing because variables named 'err' conventionally contain only
> 0 or a negative errno value. But this patch makes it possible for
> ovl_check_metacopy_xattr() to return a positive size.
It was already returning "negative, 0 or 1", so it's not fundamentally
changed. Again, this is not my code so I'd rather Amir and Miklos
decide such code style questions.
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Alexander Larsson Red Hat, Inc
alexl@xxxxxxxxxx alexander.larsson@xxxxxxxxx
