[PATCH 16/16] vfs: return -EOPNOTSUPP for fscaps from vfs_*xattr()

[Amir Goldstein]

On Wed, Nov 29, 2023 at 11:51 PM Seth Forshee (DigitalOcean)
<sforshee at kernel.org> wrote:
>
> Now that the new vfs-level interfaces are fully supported and all code
> has been converted to use them, stop permitting use of the top-level vfs
> xattr interfaces for capabilities xattrs. Unlike with ACLs we still need
> to be able to work with fscaps xattrs using lower-level interfaces in a
> handful of places, so only use of the top-level xattr interfaces is
> restricted.

Can you explain why?
Is there an inherent difference between ACLs and fscaps in that respect
or is it just a matter of more work that needs to be done?

>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>
> ---
>  fs/xattr.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 372644b15457..4b779779ad8c 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -540,6 +540,9 @@ vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
>         const void  *orig_value = value;
>         int error;
>
> +       if (!strcmp(name, XATTR_NAME_CAPS))
> +               return -EOPNOTSUPP;
> +

It this is really not expected, then it should be an assert and
please use an inline helper like is_posix_acl_xattr():

if (WARN_ON_ONCE(is_fscaps_xattr(name)))

It wouldn't hurt to add those assertions to is_posix_acl_xattr()
cases as well, but that is unrelated to your change.

Thanks,
Amir.