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Mon, 27 Jul 2020 08:12:31 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwNk/DiwCmak3npfh1kAwMumgaUwDeymyQ2rkpLTvOupt4Eaivg78zbN+F/LXbUxVxK4AsXD6b9M5yutxKLJgI= X-Received: by 2002:a05:6808:486:: with SMTP id z6mr19388061oid.56.1595862751426; Mon, 27 Jul 2020 08:12:31 -0700 (PDT) MIME-Version: 1.0 References: <20200726152532.256261-1-nsoffer@redhat.com> <20200726152532.256261-2-nsoffer@redhat.com> <1737bdc4-6192-1adb-7027-faf09bdbd92c@redhat.com> In-Reply-To: <1737bdc4-6192-1adb-7027-faf09bdbd92c@redhat.com> From: Nir Soffer Date: Mon, 27 Jul 2020 18:12:15 +0300 Message-ID: Subject: Re: [PATCH 1/2] block: nbd: Fix convert qcow2 compressed to nbd To: Eric Blake X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=205.139.110.120; envelope-from=nsoffer@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 01:44:14 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H2=-1, 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 , Max Reitz , qemu-block , Nir Soffer , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 27, 2020 at 5:04 PM Eric Blake wrote: > > On 7/26/20 10:25 AM, Nir Soffer wrote: > > When converting to qcow2 compressed format, the last step is a special > > zero length compressed write, ending in call to bdrv_co_truncate(). This > > call always fail for the nbd driver since it does not implement > > fails > > > bdrv_co_truncate(). > > Arguably, qemu-img should be taught to ignore the failure, since it is > not unique to the nbd driver. But I can live with your approach here. > > > > > For block devices, which have the same limits, the call succeeds since > > file driver implements bdrv_co_truncate(). If the caller asked to > > truncate to the same or smaller size with exact=false, the truncate > > succeeds. Implement the same logic for nbd. > > > > Example failing without this change: > > > > > > > Fixes: https://bugzilla.redhat.com/1860627 > > Signed-off-by: Nir Soffer > > --- > > block/nbd.c | 27 +++++++++++++++++++++++++++ > > 1 file changed, 27 insertions(+) > > > > diff --git a/block/nbd.c b/block/nbd.c > > index 65a4f56924..2154113af3 100644 > > --- a/block/nbd.c > > +++ b/block/nbd.c > > @@ -1966,6 +1966,30 @@ static void nbd_close(BlockDriverState *bs) > > nbd_clear_bdrvstate(s); > > } > > > > +/* > > + * NBD cannot truncate, but if the caller ask to truncate to the same size, or > > asks > > > + * to a smaller size with extact=false, there is not reason to fail the > > exact, no > > > + * operation. > > + */ > > +static int coroutine_fn nbd_co_truncate(BlockDriverState *bs, int64_t offset, > > + bool exact, PreallocMode prealloc, > > + BdrvRequestFlags flags, Error **errp) > > +{ > > + BDRVNBDState *s = bs->opaque; > > + > > + if (offset != s->info.size && exact) { > > + error_setg(errp, "Cannot resize NBD nodes"); > > + return -ENOTSUP; > > + } > > + > > + if (offset > s->info.size) { > > + error_setg(errp, "Cannot grow NBD nodes"); > > + return -EINVAL; > > + } > > + > > + return 0; > > Looks reasonable. As Max said, I wonder if we want to reject particular > preallocation modes (looking at block/file-posix.c:raw_co_truncate), in > the case where the image was resized down and then back up (since > s->info.size is constant, but the BDS size is not if inexact resize > succeeds). Do we want to fail if someone specifies -o preallocation={falloc,full}? I see we convert DRV_REQ_MAY_UNMAP to NBD_CMD_FLAG_NO_HOLE so using -o preallocation=falloc,full should be correct. But the last request zero length write request does not do anything, so failing does not look useful. > As you have a bugzilla entry, I think this is safe for -rc2; I'll be > touching up the typos and queuing it through my NBD tree later today. > > -- > Eric Blake, Principal Software Engineer > Red Hat, Inc. +1-919-301-3226 > Virtualization: qemu.org | libvirt.org >