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Subject: Re: [PATCH 11/14] nfsd: add user xattr RPC XDR encoding/decoding logic
Date:   Wed, 25 Mar 2020 23:44:56 +0000
From:   Frank van der Linden <fllinden@amazon.com>
To:     Chuck Lever <chuck.lever@oracle.com>
CC:     Bruce Fields <bfields@fieldses.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Thu, Mar 12, 2020 at 12:24:18PM -0400, Chuck Lever wrote:
> > On Mar 11, 2020, at 3:59 PM, Frank van der Linden <fllinden@amazon.com> wrote:
> > +     /*
> > +      * Unfortunately, there is no interface to only list xattrs for
> > +      * one prefix. So there is no good way to convert maxcount to
> > +      * a maximum value to pass to vfs_listxattr, as we don't know
> > +      * how many of the returned attributes will be user attributes.
> > +      *
> > +      * So, always ask vfs_listxattr for the maximum size, and encode
> > +      * as many as possible.
> > +      */
> 
> Well, this approach worries me a little bit. Wouldn't it be better if the
> VFS provided the APIs? Review by linux-fsdevel might help here.

I missed this comment initially, sorry about the slow reply.

I'll copy this one to -fsdevel for v2.

It would require a modified or new entry point to all filesystems to
support this properly, so I didn't touch it. It's not a complex
task, it just would lead to quite a bit of code churn.

- Frank