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

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.

Jess