Re: [RFC PATCH 00/35] user xattr support (RFC8276)

Chuck Lever
2019-11-05T15:44:11Z

> On Nov 4, 2019, at 5:58 PM, Bruce Fields <bfields@fieldses.org> wrote:
>
> On Mon, Nov 04, 2019 at 04:21:47PM +0000, Frank van der Linden wrote:
>> On Mon, Nov 04, 2019 at 10:36:03AM -0500, Chuck Lever wrote:
>>>
>>> Following the server's local file systems' mount options seems like a
>>> good way to go. In particular, is there a need to expose user xattrs
>>> on the server host, but prevent NFS clients' access to them? I can't
>>> think of one.
>>
>> Ok, that sounds fine to me - I'll remove the user_xattr export flag,
>> and we had already agreed to do away with the CONFIGs.
>>
>> That leaves one last item with regard to enabling support: the client side
>> mount option. I assume the [no]user_xattr option should work the same as
>> with other filesystems. What about the default setting?
>
> Just checking code for other filesystems quickly; if I understand right:
>
> - ext4 has user_xattr and nouser_xattr options, but you get a
> deprecation warning if you try to use the latter;
> - xfs doesn't support either option;
> - cifs supports both, with xattr support the default.
>
> Not necessarily my call, but just for simplicity's sake, I'd probably
> leave out the option and see if anybody complains.

Agree, I would leave it out to begin with. Anyone on linux-fsdevel,
feel free to chime in here about why some other file systems have
this mount option. History lessons welcome.

>> Also, currently, my code does not fail the mount operation if user xattrs
>> are asked for, but the server does not support them. It just doesn't
>> set NFS_CAP_XATTR for the server, and the xattr handler entry points
>> eturn -EOPNOTSUPP, as they check for NFS_CAP_XATTR. What's the preferred
>> behavior there?
>
> getxattr(2) under ERRORS says:
>
> ENOTSUP
> Extended attributes are not supported by the filesystem,
> or are disabled.
>
> so I'm guessing just erroring out is clearest.

IMO on the client, we want getxattr failure behavior to be consistent among:

- A version of NFS that does not support xattrs at all (say, v3)

- A version of NFS that can support them but doesn't (say, NFSv4.2 before these patches)

- A version of NFS that can support them, but the server doesn't

- A version of NFS that can support them, a server that can support them, but it's filesystem doesn't

> I also see there's an EOPNOTSUPP return in the nouser_xattr case in
> ext4_xattr_user_get. (errno(3) says ENOTSUP and EOPNOTSUPP are the same
> value on Linux.)
>
> --b.

--
Chuck Lever
chucklever@gmail.com