linux-kernel - Re: [PATCH v2] vfs: prevent copy_file

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Message-ID: <CAOQ4uxjGkm0Pn84UW6JKSK3mFkrPKykfkXDLL1V4YPSgAOXULA@mail.gmail.com>
Date:   Thu, 18 Feb 2021 14:49:10 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Luis Henriques <lhenriques@...e.de>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        Steve French <sfrench@...ba.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <dchinner@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Ian Lance Taylor <iant@...gle.com>,
        Luis Lozano <llozano@...omium.org>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH v2] vfs: prevent copy_file_range to copy across devices

On Thu, Feb 18, 2021 at 2:14 PM Luis Henriques <lhenriques@...e.de> wrote:
>
> Luis Henriques <lhenriques@...e.de> writes:
>
> > Amir Goldstein <amir73il@...il.com> writes:
> >
> >> On Thu, Feb 18, 2021 at 9:42 AM Christoph Hellwig <hch@...radead.org> wrote:
> >>>
> >>> Looks good:
> >>>
> >>> Reviewed-by: Christoph Hellwig <hch@....de>
> >>>
> >>> This whole idea of cross-device copie has always been a horrible idea,
> >>> and I've been arguing against it since the patches were posted.
> >>
> >> Ok. I'm good with this v2 as well, but need to add the fallback to
> >> do_splice_direct()
> >> in nfsd_copy_file_range(), because this patch breaks it.
> >>
> >> And the commit message of v3 is better in describing the reported issue.
> >
> > Except that, as I said in a previous email, v2 doesn't really fix the
> > issue: all the checks need to be done earlier in generic_copy_file_checks().
> >
> > I'll work on getting v4, based on v2 and but moving the checks and
> > implementing your review suggestions to v3 (plus this nfs change).
>
> There's something else:
>
> The filesystems (nfs, ceph, cifs, fuse) rely on the fallback to
> generic_copy_file_range() if something's wrong.  And this "something's
> wrong" is fs specific.  For example: in ceph it is possible to offload the
> file copy to the OSDs even if the files are in different filesystems as
> long as these filesystems are on the *same* ceph cluster.  If the copy
> being done is across two different clusters, then the copy reverts to
> splice.  This means that the boilerplate code being removed in v2 of this
> patch needs to be restored and replace by:
>
>         ret = __ceph_copy_file_range(src_file, src_off, dst_file, dst_off,
>                                      len, flags);
>
>         if (ret == -EOPNOTSUPP || ret == -EXDEV)
>                 ret = do_splice_direct(src_file, &src_off, dst_file, &dst_off,
>                                        len > MAX_RW_COUNT ? MAX_RW_COUNT : len,
>                                        flags);
>         return ret;
>

Why not leave the filesystem code as is and leave the
generic_copy_file_range() helper? Less churn.

Then nfsd_copy_file_range() can also fallback to generic_copy_file_range().

Thanks,
Amir.