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

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Date:   Thu, 12 Dec 2019 12:47:47 -0500
From:   Laura Abbott <labbott@...hat.com>
To:     Ilya Dryomov <idryomov@...il.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Jeremi Piotrowski <jeremi.piotrowski@...il.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vfs: Don't reject unknown parameters

On 12/12/19 12:13 PM, Ilya Dryomov wrote:
> On Thu, Dec 12, 2019 at 3:51 PM Laura Abbott <labbott@...hat.com> 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@gentoo-tp.home/
>> Reported-by: Jeremi Piotrowski <jeremi.piotrowski@...il.com>
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1781863
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>>   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