Re: [PATCH v2 0/4] NFSD: Add READ_PLUS support

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jan 28, 2015 at 03:42:53PM -0500, Anna.Schumaker@netapp.com wrote:
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> 
> These patches add server support for the NFS v4.2 operation READ_PLUS.
> 
> I noticed a race condition in the 3rd patch when I start needing vfs_llseek()
> to determine if I should encode the next segment as either data or a hole.  It
> is possible that the file could change on us between each of the seek calls,
> so we don't know if we are actually at a hole or data segment.  I don't want to
> add new locks to the NFS server for this case, so instead I've decided to
> encode any "quantum data" segments as if they were actually data.
> 
> I tested these patches using xfstests, specificially generic/075, generic/091,
> generic/112, generic/127, generic/210, and generic/263.  Additionally, three
> new tests are run once READ_PLUS support has been added: generic/213,
> generic/214, and generic/228.

Why do theses test start working when you use READ_PLUS?  They should
only depend on ALLOCATE support, and maybe SEEK if we're trying to
figure out information about mappings somehow.