From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 496C8C49ED7 for ; Fri, 20 Sep 2019 07:25:54 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1F12C2086A for ; Fri, 20 Sep 2019 07:25:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F12C2086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ispras.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:53036 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iBDIf-0007oP-6O for qemu-devel@archiver.kernel.org; Fri, 20 Sep 2019 03:25:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56222) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iBDHo-0007Du-Cu for qemu-devel@nongnu.org; Fri, 20 Sep 2019 03:25:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iBDHm-0001MY-Uy for qemu-devel@nongnu.org; Fri, 20 Sep 2019 03:25:00 -0400 Received: from mail.ispras.ru ([83.149.199.45]:46030) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1iBDHm-0001LK-LD for qemu-devel@nongnu.org; Fri, 20 Sep 2019 03:24:58 -0400 Received: from PASHAISP (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id B61F154006A; Fri, 20 Sep 2019 10:24:55 +0300 (MSK) From: "Pavel Dovgalyuk" To: "'Kevin Wolf'" References: <20190918091831.GD5207@localhost.localdomain> <001201d56e02$9d88b5f0$d89a21d0$@ru> <20190918093305.GF5207@localhost.localdomain> <001401d56e04$b93c02a0$2bb407e0$@ru> <20190918094436.GG5207@localhost.localdomain> <001501d56e06$bbd7aa30$3386fe90$@ru> <20190919085302.GA10163@localhost.localdomain> <001901d56ec9$620ae260$2620a720$@ru> <20190919112702.GC10163@localhost.localdomain> <001a01d56ee3$4354a530$c9fdef90$@ru> <20190919130005.GF10163@localhost.localdomain> In-Reply-To: <20190919130005.GF10163@localhost.localdomain> Subject: RE: [for-4.2 PATCH 3/6] replay: update docs for record/replay with block devices Date: Fri, 20 Sep 2019 10:25:00 +0300 Message-ID: <002401d56f84$83900e40$8ab02ac0$@ru> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook 12.0 Content-Language: ru Thread-Index: AdVu6jGMvI/1655mR8ugxifB44kziQAmiPDw X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 83.149.199.45 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: peter.maydell@linaro.org, pavel.dovgaluk@ispras.ru, quintela@redhat.com, ciro.santilli@gmail.com, jasowang@redhat.com, crosthwaite.peter@gmail.com, qemu-devel@nongnu.org, armbru@redhat.com, alex.bennee@linaro.org, maria.klimushenkova@ispras.ru, mst@redhat.com, kraxel@redhat.com, boost.lists@gmail.com, thomas.dullien@googlemail.com, pbonzini@redhat.com, mreitz@redhat.com, artem.k.pisarenko@gmail.com, dgilbert@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > From: Kevin Wolf [mailto:kwolf@redhat.com] > Am 19.09.2019 um 14:10 hat Pavel Dovgalyuk geschrieben: > > > From: Kevin Wolf [mailto:kwolf@redhat.com] > > > Am 19.09.2019 um 11:05 hat Pavel Dovgalyuk geschrieben: > > > > > From: Kevin Wolf [mailto:kwolf@redhat.com] > > > > > > > > > > > > > > However, global -snapshot is just a convenient shortcut for specifying > > > > > > > snapshot=on for all -drive arguments. So if -snapshot is incompatible > > > > > > > with replay, shouldn't manually marking all drives as snapshot=on be > > > > > > > incompatible as well? > > > > > > > > > > > > > > Maybe you're really interested in some specific drive not having > > > > > > > snapshot=on? But then it might be better to check that specific drive > > > > > > > instad of forbidding just the shortcut for setting it. > > > > > > > > > > > > -snapshot adds the flag for top-level drive, making driver operations > > > > > > dependent on temporary file structure. > > > > > > > > > > > > Moving this overlay beneath blkreplay driver makes drive operations > > > > > > deterministic for the top-level device. > > > > > > > > > > So the real requirement is that blkreplay is the top-level node of any > > > > > guest device, right? And only because of this, you can't use -snapshot > > > > > (or snapshot=on on the blkreplay driver). > > > > > > > > > > If we instead check e.g. in blk_insert_bs() or blk_attach_dev() that in > > > > > record/replay mode, the root node of the BlockBackend is blkreplay, > > > > > wouldn't we catch many more incorrect setups? > > > > > > > > That sounds interesting. > > > > Will it help to check that every backend is connected to blkreplay? > > > > > > Yes, it would return an error when you try to attach a non-blkreplay > > > node to a BlockBackend (and every guest device uses a BlockBackend). > > > > > > Note that this restriction would currently make block jobs unavailable > > > on non-blkreplay nodes as they also use BlockBackends internally (though > > > this is going to change in the long run). I believe this restriction is > > > harmless and the typical replay use case doesn't involve any block jobs, > > > but if you do think it's a problem, blk_attach_dev() would be the place > > > that affects only devices. > > > > > > > How then this check has to be done? > > > > > > Only compile-tested, but maybe something like below? > > > > > > Kevin > > > > > > diff --git a/include/block/block_int.h b/include/block/block_int.h > > > index 0422acdf1c..9fa72bea51 100644 > > > --- a/include/block/block_int.h > > > +++ b/include/block/block_int.h > > > @@ -955,6 +955,7 @@ static inline BlockDriverState *backing_bs(BlockDriverState *bs) > > > extern BlockDriver bdrv_file; > > > extern BlockDriver bdrv_raw; > > > extern BlockDriver bdrv_qcow2; > > > +extern BlockDriver bdrv_blkreplay; > > > > > > int coroutine_fn bdrv_co_preadv(BdrvChild *child, > > > int64_t offset, unsigned int bytes, QEMUIOVector *qiov, > > > diff --git a/block/blkreplay.c b/block/blkreplay.c > > > index 2b7931b940..16a4f1df6a 100644 > > > --- a/block/blkreplay.c > > > +++ b/block/blkreplay.c > > > @@ -126,7 +126,7 @@ static int coroutine_fn blkreplay_co_flush(BlockDriverState *bs) > > > return ret; > > > } > > > > > > -static BlockDriver bdrv_blkreplay = { > > > +BlockDriver bdrv_blkreplay = { > > > .format_name = "blkreplay", > > > .instance_size = 0, > > > > > > diff --git a/block/block-backend.c b/block/block-backend.c > > > index 1c605d5444..c57d3d9fdf 100644 > > > --- a/block/block-backend.c > > > +++ b/block/block-backend.c > > > @@ -17,6 +17,7 @@ > > > #include "block/throttle-groups.h" > > > #include "hw/qdev-core.h" > > > #include "sysemu/blockdev.h" > > > +#include "sysemu/replay.h" > > > #include "sysemu/runstate.h" > > > #include "qapi/error.h" > > > #include "qapi/qapi-events-block.h" > > > @@ -808,6 +809,12 @@ void blk_remove_bs(BlockBackend *blk) > > > int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp) > > > { > > > ThrottleGroupMember *tgm = &blk->public.throttle_group_member; > > > + > > > + if (replay_mode != REPLAY_MODE_NONE && bs->drv != &bdrv_blkreplay) { > > > + error_setg(errp, "Root node must be blkreplay"); > > > + return -ENOTSUP; > > > + } > > > > I guess this is opposite direction - bs->drv is bdrv_file. > > And we should check its parent. > > If bs->drv is bdrv_file, you want this to fail because only > bdrv_blkreplay should be able to be attached to devices. There was a regular rr invocation (as described in docs). And bs->drv always was a pointer to bdrv_file: for original image, and for temporary snapshot. Pavel Dovgalyuk