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Date:   Thu, 12 Mar 2020 21:15:55 +0000
From:   Frank van der Linden <fllinden@amazon.com>
To:     "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
CC:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 03/13] NFSv4.2: query the server for extended attribute
 support
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On Thu, Mar 12, 2020 at 08:51:39PM +0000, Frank van der Linden wrote:
> 1) The xattr_support attribute exists
> 2) The xattr support attribute exists *and* it's true for the root fh
> 
> Currently the code does 2) in one operation. That might not be 100%
> correct - the RFC does mention that (section 8.2):
> 
> "Before interrogating this attribute using GETATTR, a client should
>  determine whether it is a supported attribute by interrogating the
>  supported_attrs attribute."
> 
> That's a "should", not a "MUST", but it's still waving its finger
> at you not to do this.
> 
> Since 8.2.1 says:
> 
> "However, a client may reasonably assume that a server
>  (or file system) that does not support the xattr_support attribute
>  does not provide xattr support, and it acts on that basis."
> 
> ..I think you're right, and the code should just use the existence
> of the attribute as a signal that the server knows about xattrs -
> operations should still error out correctly if it doesn't.
> 
> I'll make that change, thanks.

..or, alternatively, only query xattr_support in nfs4_server_capabilities,
and then its actual value, if it exists, in nfs4_fs_info.

Any opinions on this?

- Frank