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Date:   Fri, 4 Sep 2020 10:29:23 -0400
From:   Bruce Fields <bfields@fieldses.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Anna Schumaker <schumaker.anna@gmail.com>,
        Bruce Fields <bfields@redhat.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v4 2/5] NFSD: Add READ_PLUS data support
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On Fri, Sep 04, 2020 at 10:07:22AM -0400, Chuck Lever wrote:
> My primary concern is that the result of a file copy operation should
> look the same on NFS/TCP (with READ_PLUS) and NFS/RDMA (with SEEK_DATA/HOLE).

I'm not sure what you mean.

I don't see the spec providing any guarantee of consistency between
READ_PLUS and SEEK.  It also doesn't guarantee that the results tell you
anything about how the file is actually stored--a returned "hole" could
represent an unallocated segment, or a fully allocated segment that's
filled with zeroes, or some combination.

So, for example, if you implemented an optimized copy that used
ALLOCATE, DEALLOCATE, SEEK and/or READ_PLUS to avoid reading and writing
a lot of zeroes--there's no guarantee that the target file would end up
allocated in the same way as the source.

--b.