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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Thu, 25 Oct 2018 07:58:57 +0300
Message-ID: <CAOQ4uxgW+AAxGszy=rsNCZLAJPpJbz6O4Xtnje-=WeDo+oATag@mail.gmail.com>
Subject: Re: [PATCH v1 02/11] VFS permit cross device vfs_copy_file_range
To:     Olga Kornievskaia <olga.kornievskaia@gmail.com>
Cc:     Jeff Layton <jlayton@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        fweimer@redhat.com, Steve French <smfrench@gmail.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Christoph Hellwig <hch@lst.de>, linux-api@vger.kernel.org
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Sender: linux-nfs-owner@vger.kernel.org
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On Wed, Oct 24, 2018 at 10:59 PM Olga Kornievskaia
<olga.kornievskaia@gmail.com> wrote:
>
[...]
> It feels like folks are now ok with either the check being in the
> drivers or doing the check in the VFS layer.
>
> I'm picking the choice of not doing the check in the VFS layer because
> it allows for do_splice_direct() by any caller.

I'm sorry, but this reasoning in flawed and this is not the reason that
Matthew promoted not doing same fs type check in vfs.
You did not understand the option that I was promoting to begin with.
What I suggested was:

1. Remove current same sb check in beginning of vfs_copy_file_range()
2. Check sb && ->clone_file_range
3. Check same sb type && ->copy_file_range
4. Cross fs do_splice_direct()

It's fine that you chose not to check for same fs type in VFS before calling
copy_file_range() method, but still requires an ACK from Al that he agrees
with passing in file * of another filesystem on the interface.

> I'm about to submit
> the new version of the patches (this time I will include the NFS patch
> series). We can continue with the discussion on the new version.
>
> I have added checks for the CIFS and OverlayFS to be consistent with
> the previous behavior -- no cross-device copy_offload, I assume if and
> when those file systems are ready to make use of it they'll remove the
> check.
>

Actually overlayfs code is "ready" for cross sb copy, but neither nfs nor
cifs are supported as upper file system, so it doesn't matter much.

Thanks,
Amir.