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Subject: Re: [PATCH v4 2/5] NFSD: Add READ_PLUS data support
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20200904142923.GE26706@fieldses.org>
Date:   Fri, 4 Sep 2020 10:36:36 -0400
Cc:     Anna Schumaker <schumaker.anna@gmail.com>,
        Bruce Fields <bfields@redhat.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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To:     Bruce Fields <bfields@fieldses.org>
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> On Sep 4, 2020, at 10:29 AM, Bruce Fields <bfields@fieldses.org> =
wrote:
>=20
> 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).
>=20
> I'm not sure what you mean.
>=20
> I don't see the spec providing any guarantee of consistency between
> READ_PLUS and SEEK.

IMO this is an implementation quality issue, not a spec compliance
issue.


> 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.

Understood, but the resulting copied file should look the same whether
it was read from the server using READ_PLUS or SEEK_DATA/HOLE.


> 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.


--
Chuck Lever