Re: [PATCH] vfs: Don't reject unknown parameters

[Laura Abbott]

On 12/12/19 12:13 PM, Ilya Dryomov wrote:
> On Thu, Dec 12, 2019 at 3:51 PM Laura Abbott <labbott@xxxxxxxxxx> wrote:
> > The new mount API currently rejects unknown parameters if the
> > filesystem doesn't have doesn't take any arguments. This is
> > unfortunately a regression from the old API which silently
> > ignores extra arguments. This is easly seen with the squashfs
> > conversion (5a2be1288b51 ("vfs: Convert squashfs to use the new
> > mount API")) which now fails to mount with extra options. Just
> > get rid of the error.
> >
> > Fixes: 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock
> > creation/configuration context")
> > Link: https://lore.kernel.org/lkml/20191130181548.GA28459@xxxxxxxxxxxxxx/
> > Reported-by: Jeremi Piotrowski <jeremi.piotrowski@xxxxxxxxx>
> > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1781863
> > Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> > ---
> >   fs/fs_context.c | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/fs/fs_context.c b/fs/fs_context.c
> > index 138b5b4d621d..7ec20b1f8a53 100644
> > --- a/fs/fs_context.c
> > +++ b/fs/fs_context.c
> > @@ -160,8 +160,7 @@ int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
> >                  return 0;
> >          }
> >
> > -       return invalf(fc, "%s: Unknown parameter '%s'",
> > -                     fc->fs_type->name, param->key);
> > +       return 0;
> >   }
> >   EXPORT_SYMBOL(vfs_parse_fs_param);
>
> Hi Laura,
>
> I'm pretty sure this is a regression for all other filesystems
> that used to check for unknown tokens and return an error from their
> ->mount/fill_super/etc methods before the conversion.
>
> All filesystems that provide ->parse_param expect that ENOPARAM is
> turned into an error with an error message.  I think we are going to
> need something a bit more involved in vfs_parse_fs_param(), or just
> a dummy ->parse_param for squashfs that would always return 0.
>
> Thanks,
>
>                  Ilya

Good point, I think I missed how that code flow worked for printing
out the error. I debated putting in a dummy parse_param but I
figured that squashfs wouldn't be the only fs that didn't take
arguments (it's in the minority but certainly not the only one).
I'll see about reworking the flow unless Al/David want to
see the dummy parse_param or give a patch.

Thanks,
Laura