Re: git: bfc8e3308bee - main - ext2fs: Fix the size of struct ufid and add a static assert

On Thu, Dec 5, 2024 at 6:40 PM Jessica Clarke <jrtc27@freebsd.org> wrote:
>
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> On 6 Dec 2024, at 02:06, Rick Macklem <rmacklem@FreeBSD.org> wrote:
> >
> > The branch main has been updated by rmacklem:
> >
> > URL: https://cgit.FreeBSD.org/src/commit/?id=bfc8e3308bee23d0f7836d57f32ed8d47da02627
> >
> > commit bfc8e3308bee23d0f7836d57f32ed8d47da02627
> > Author:     Rick Macklem <rmacklem@FreeBSD.org>
> > AuthorDate: 2024-12-06 02:05:06 +0000
> > Commit:     Rick Macklem <rmacklem@FreeBSD.org>
> > CommitDate: 2024-12-06 02:05:06 +0000
> >
> >    ext2fs: Fix the size of struct ufid and add a static assert
> >
> >    File system specific *fid structures are copied into the generic
> >    struct fid defined in sys/mount.h.
> >    As such, they cannot be larger than struct fid.
> >
> >    This patch packed the structure and checks via a __Static_assert().
> >
> >    Reviewed by:    markj
> >    MFC after:      2 weeks
> > ---
> > sys/fs/ext2fs/ext2_vnops.c | 2 ++
> > sys/fs/ext2fs/inode.h      | 2 +-
> > 2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/sys/fs/ext2fs/ext2_vnops.c b/sys/fs/ext2fs/ext2_vnops.c
> > index dfbb11f75421..064c10bd18b2 100644
> > --- a/sys/fs/ext2fs/ext2_vnops.c
> > +++ b/sys/fs/ext2fs/ext2_vnops.c
> > @@ -1889,6 +1889,8 @@ ext2_vptofh(struct vop_vptofh_args *ap)
> > {
> > struct inode *ip;
> > struct ufid *ufhp;
> > + _Static_assert(sizeof(struct ufid) <= sizeof(struct fid),
> > +    "struct ufid cannot be larger than struct fid");
> >
> > ip = VTOI(ap->a_vp);
> > ufhp = (struct ufid *)ap->a_fhp;
> > diff --git a/sys/fs/ext2fs/inode.h b/sys/fs/ext2fs/inode.h
> > index 9ee1b5672da6..63102deb10b0 100644
> > --- a/sys/fs/ext2fs/inode.h
> > +++ b/sys/fs/ext2fs/inode.h
> > @@ -191,7 +191,7 @@ struct ufid {
> > uint16_t ufid_pad; /* Force 32-bit alignment. */
> > ino_t ufid_ino; /* File number (ino). */
> > uint32_t ufid_gen; /* Generation number. */
> > -};
> > +} __packed;
>
> Why not just swap ufid_ino and ufid_gen? This will give worse codegen
> on architectures that don’t assume fast unaligned access.
You can commit such a change if you'd like, as far as I am concerned.

I suspect few (if any) export ext2fs file systems anyhow, so this structure
is unlikely to ever be used.

There was a discussion on phabricator in D47879 about reordering
entries and the consensus there seemed to be avoid doing that,
although admittedly I think they were referring to the first two fields,
which match the ones in the generic "struct fid".

rick

>
> Jess
>