[RFC] use a shared lock for VOP_GETEXTATTR

[mdf at FreeBSD.org]

On Wed, Mar 27, 2013 at 10:32 PM, Konstantin Belousov
<kostikbel at gmail.com> wrote:
> On Wed, Mar 27, 2013 at 06:37:51PM -0700, mdf at FreeBSD.org wrote:
>> VOP_GETEXTATTR is currently called with an exclusive lock, which seems
>> like overkill for what is essentially a read operation.  I had a look
>> over the various in-tree filesystems and it didn't look like any of
>> them will have a problem if a shared-mode lock is used for
>> vop_getextattr.
>>
>> Does anyone know otherwise?  Is someone using extended attributes
>> regularly who can test this?
>
> I think this change should be fine. At least it seems to for UFS.
>
> What other filesystems did you audited ?

I looked over zfs, pseudofs, unionfs, ffs/ufs.  None seemed to have
any asserts on the lock type nor anything that looked like it would
try to modify anything.  zfs, I think it was, even used VOP_ISLOCKED
to get the lock type in one path (but I think that was after a
lookup(), so it may have been on a different vnode).

Cheers,
matthew