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Subject: Re: copy offload support and absent file system
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <CAN-5tyE25JYUbnhvRD32_ZxyALdXd+emy2qK315DeXb+DgLn1Q@mail.gmail.com>
Date:   Fri, 26 Oct 2018 11:43:40 -0400
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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To:     Olga Kornievskaia <aglo@umich.edu>
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> On Oct 26, 2018, at 11:39 AM, Olga Kornievskaia <aglo@umich.edu> =
wrote:
>=20
> On Fri, Oct 26, 2018 at 11:04 AM Chuck Lever <chuck.lever@oracle.com> =
wrote:
>>=20
>>=20
>>=20
>>> On Oct 26, 2018, at 8:54 AM, Olga Kornievskaia <aglo@umich.edu> =
wrote:
>>>=20
>>> Hi Chuck,
>>>=20
>>> In the context of doing a copy between different "types" of
>>> filesystems, it was pointed out to me that NFS has many types:
>>> nfs4_fs_type, nfs4_remote_fs_type, nfs4_remote_referral_fs_type,
>>> nfs4_referral_fs_type. So doing a simple check that fs type of "in"
>>> and "out" might not be sufficient. Do you see any issues allowing a
>>> copy offload between different types? Basically checking that "in" =
and
>>> "out" descriptions come from any of the these types?
>>=20
>> I'm no expert... so what follows is an uninformed opinion.
>=20
> I was wondering if there was anything different about the
> migrated/replicated filesystem that maybe say they are typically
> read-only and thus doing a copy there wouldn't be appropriate. But it
> sounds like you don't see anything special about doing a copy from
> nfs4_fs_type to say nfs_remote_fs_type?

If I recall correctly the distinction between these "types" is
the way they are attached to the client's filesystem namespace.
I don't believe that would have any impact on whether copy
offload is supported or not.


>> All of these are NFSv4 file systems. But I don't think that's an
>> adequate check (it's necessary, but not sufficient).
>=20
>=20
>> The minor version of the mount point has to be 2 or higher, and
>> the client must confirm that the mounted server supports copy
>> offload (because all NFSv4.2 features are OPTIONAL).
>=20
> I agree that we should check for 4.2 versioning but the latter I don't
> think is necessary, as the COPY call will just gets not supported
> error (we already have the capability check for CAP_COPY inside of
> nfs42_proc_copy , just in case we already sent one copy and then
> negated the capabilities).

The COPY call could also return EROFS if the destination filesystem
is a read-only replica.

--
Chuck Lever