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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Fri, 26 Oct 2018 12:01:55 -0400
Message-ID: <CAN-5tyGq2S9EvUFWGJDC+YZhd-WXN7_gpA71fce49MaF8no0bw@mail.gmail.com>
Subject: Re: copy offload support and absent file system
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
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On Fri, Oct 26, 2018 at 11:44 AM Chuck Lever <chuck.lever@oracle.com> wrote:
>
>
>
> > On Oct 26, 2018, at 11:39 AM, Olga Kornievskaia <aglo@umich.edu> wrote:
> >
> > On Fri, Oct 26, 2018 at 11:04 AM Chuck Lever <chuck.lever@oracle.com> wrote:
> >>
> >>
> >>
> >>> On Oct 26, 2018, at 8:54 AM, Olga Kornievskaia <aglo@umich.edu> wrote:
> >>>
> >>> Hi Chuck,
> >>>
> >>> 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?
> >>
> >> I'm no expert... so what follows is an uninformed opinion.
> >
> > 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).
> >
> >
> >> 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).
> >
> > 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.

In such case, I would hope that the OPEN of the destination file for
writing would fail and we won't even get to the COPY.

>
> --
> Chuck Lever
>
>
>