Re: [RFC 1/1] NFSD add vfs_fsync after async copy is done

[dai.ngo@xxxxxxxxxx]

On 4/22/21 10:27 AM, Olga Kornievskaia wrote:
> On Thu, Apr 22, 2021 at 12:54 PM <dai.ngo@xxxxxxxxxx> wrote:
> > On 4/22/21 9:19 AM, Olga Kornievskaia wrote:
> > > From: Olga Kornievskaia <kolga@xxxxxxxxxx>
> > >
> > > Currently, the server does all copies as NFS_UNSTABLE. For synchronous
> > > copies linux client will append a COMMIT to the COPY compound but for
> > > async copies it does not (because COMMIT needs to be done after all
> > > bytes are copied and not as a reply to the COPY operation).
> > >
> > > However, in order to save the client doing a COMMIT as a separate
> > > rpc, the server can reply back with NFS_FILE_SYNC copy. This patch
> > > proposed to add vfs_fsync() call at the end of the async copy.
> > >
> > > Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
> > > ---
> > >    fs/nfsd/nfs4proc.c | 22 +++++++++++++++++-----
> > >    1 file changed, 17 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > index 66dea2f1eed8..c6f45f67d59b 100644
> > > --- a/fs/nfsd/nfs4proc.c
> > > +++ b/fs/nfsd/nfs4proc.c
> > > @@ -1536,19 +1536,21 @@ static const struct nfsd4_callback_ops nfsd4_cb_offload_ops = {
> > >        .done = nfsd4_cb_offload_done
> > >    };
> > >
> > > -static void nfsd4_init_copy_res(struct nfsd4_copy *copy, bool sync)
> > > +static void nfsd4_init_copy_res(struct nfsd4_copy *copy, bool sync,
> > > +                             bool committed)
> > >    {
> > > -     copy->cp_res.wr_stable_how = NFS_UNSTABLE;
> > > +     copy->cp_res.wr_stable_how = committed ? NFS_FILE_SYNC : NFS_UNSTABLE;
> > >        copy->cp_synchronous = sync;
> > >        gen_boot_verifier(&copy->cp_res.wr_verifier, copy->cp_clp->net);
> > >    }
> > >
> > > -static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy)
> > > +static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy, bool *committed)
> > >    {
> > >        ssize_t bytes_copied = 0;
> > >        size_t bytes_total = copy->cp_count;
> > >        u64 src_pos = copy->cp_src_pos;
> > >        u64 dst_pos = copy->cp_dst_pos;
> > > +     __be32 status;
> > >
> > >        do {
> > >                if (kthread_should_stop())
> > > @@ -1563,6 +1565,15 @@ static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy)
> > >                src_pos += bytes_copied;
> > >                dst_pos += bytes_copied;
> > >        } while (bytes_total > 0 && !copy->cp_synchronous);
> > > +     /* for a non-zero asynchronous copy do a commit of data */
> > > +     if (!copy->cp_synchronous && bytes_copied > 0) {
> > I think (bytes_copied > 0) should be (bytes_total < copy->cp_count).
> I don't think so. A successful async copy should never be less the
> requested bytes.

nfsd_copy_file_range can return 0 on the last write in the loop which
causes the test (bytes_copied > 0) to fail which then skipping the
commit. The check (bytes_total < copy->cp_count) says do the commit
if there are any bytes successfully written so far.

-Dai

> > -Dai
> >
> > > +             down_write(&copy->nf_dst->nf_rwsem);
> > > +             status = vfs_fsync_range(copy->nf_dst->nf_file,
> > > +                                      copy->cp_dst_pos, bytes_copied, 0);
> > > +             up_write(&copy->nf_dst->nf_rwsem);
> > > +             if (!status)
> > > +                     *committed = true;
> > > +     }
> > >        return bytes_copied;
> > >    }
> > >
> > > @@ -1570,15 +1581,16 @@ static __be32 nfsd4_do_copy(struct nfsd4_copy *copy, bool sync)
> > >    {
> > >        __be32 status;
> > >        ssize_t bytes;
> > > +     bool committed = false;
> > >
> > > -     bytes = _nfsd_copy_file_range(copy);
> > > +     bytes = _nfsd_copy_file_range(copy, &committed);
> > >        /* for async copy, we ignore the error, client can always retry
> > >         * to get the error
> > >         */
> > >        if (bytes < 0 && !copy->cp_res.wr_bytes_written)
> > >                status = nfserrno(bytes);
> > >        else {
> > > -             nfsd4_init_copy_res(copy, sync);
> > > +             nfsd4_init_copy_res(copy, sync, committed);
> > >                status = nfs_ok;
> > >        }