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Fri, 28 Aug 2020 08:13:29 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH 4/6] block, migration: add bdrv_finalize_vmstate helper References: <20200709132644.28470-1-den@openvz.org> <20200709132644.28470-5-den@openvz.org> <20200827125846.GA1429165@redhat.com> <20200827130645.GT192458@redhat.com> Date: Fri, 28 Aug 2020 08:13:29 +0200 In-Reply-To: <20200827130645.GT192458@redhat.com> ("Daniel P. =?utf-8?Q?Be?= =?utf-8?Q?rrang=C3=A9=22's?= message of "Thu, 27 Aug 2020 14:06:45 +0100") Message-ID: <87wo1j47sm.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/28 02:09:03 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.959, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , qemu-block@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Denis Plotnikov , Stefan Hajnoczi , "Denis V. Lunev" , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 writes: > On Thu, Aug 27, 2020 at 04:02:38PM +0300, Denis V. Lunev wrote: >> On 8/27/20 3:58 PM, Daniel P. Berrang=C3=A9 wrote: >> > On Thu, Jul 09, 2020 at 04:26:42PM +0300, Denis V. Lunev wrote: >> >> Right now bdrv_fclose() is just calling bdrv_flush(). >> >> >> >> The problem is that migration code is working inefficiently from bloc= k >> >> layer terms and are frequently called for very small pieces of >> >> unaligned data. Block layer is capable to work this way, but this is = very >> >> slow. >> >> >> >> This patch is a preparation for the introduction of the intermediate >> >> buffer at block driver state. It would be beneficial to separate >> >> conventional bdrv_flush() from closing QEMU file from migration code. >> >> >> >> The patch also forces bdrv_finalize_vmstate() operation inside >> >> synchronous blk_save_vmstate() operation. This helper is used from >> >> qemu-io only. >> >> >> >> Signed-off-by: Denis V. Lunev >> >> Reviewed-by: Vladimir Sementsov-Ogievskiy >> >> CC: Kevin Wolf >> >> CC: Max Reitz >> >> CC: Stefan Hajnoczi >> >> CC: Fam Zheng >> >> CC: Juan Quintela >> >> CC: "Dr. David Alan Gilbert" >> >> CC: Denis Plotnikov >> >> --- >> >> block/block-backend.c | 6 +++++- >> >> block/io.c | 15 +++++++++++++++ >> >> include/block/block.h | 5 +++++ >> >> migration/savevm.c | 4 ++++ >> >> 4 files changed, 29 insertions(+), 1 deletion(-) >> >> diff --git a/migration/savevm.c b/migration/savevm.c >> >> index 45c9dd9d8a..d8a94e312c 100644 >> >> --- a/migration/savevm.c >> >> +++ b/migration/savevm.c >> >> @@ -150,6 +150,10 @@ static ssize_t block_get_buffer(void *opaque, ui= nt8_t *buf, int64_t pos, >> >> =20 >> >> static int bdrv_fclose(void *opaque, Error **errp) >> >> { >> >> + int err =3D bdrv_finalize_vmstate(opaque); >> >> + if (err < 0) { >> >> + return err; >> > This is returning an error without having populating 'errp' which mean= s >> > the caller will be missing error diagnosis >>=20 >> but this behaves exactly like the branch below, >> bdrv_flush() could return error too and errp >> is not filled in the same way. > > Doh, it seems the only caller passes NULL for the errp too, > so it is a redundant parameter. So nothing wrong with your > patch after all. Not setting an error on failure is plainly wrong. If it works because all callers pass NULL, then the obvious fix is to drop the @errp parameter. I agree it's not this patch's fault. It needs fixing anyway. If you have to respin for some other reason, including a fix would be nice.