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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:40842 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kIr8x-0003pH-LX for qemu-devel@archiver.kernel.org; Thu, 17 Sep 2020 06:27:59 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34006) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kIr0m-0003G2-EA for qemu-devel@nongnu.org; Thu, 17 Sep 2020 06:19:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23611) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kIr0k-0004TF-BF for qemu-devel@nongnu.org; Thu, 17 Sep 2020 06:19:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600337969; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <07832208-dcc8-8e33-c7e7-05f9c891fec3@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="E8pNq7L9f6QaDJP8JNi3cux5srbrnOdgm" Received-SPF: pass client-ip=216.205.24.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/17 02:01:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -51 X-Spam_score: -5.2 X-Spam_bar: ----- X-Spam_report: (-5.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.062, 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=ham 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: kwolf@redhat.com, eshenitz@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --E8pNq7L9f6QaDJP8JNi3cux5srbrnOdgm Content-Type: multipart/mixed; boundary="h9SGduBELzdgVLvEONw1T4EYz9rlfxoY6" --h9SGduBELzdgVLvEONw1T4EYz9rlfxoY6 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 15.09.20 15:31, Eric Blake wrote: > On 9/15/20 3:57 AM, Max Reitz wrote: >> On 14.09.20 21:10, Eric Blake wrote: >>> If you have the chain 'base.qcow2 <- top.qcow2' and want to merge a >>> bitmap from top into base, qemu-img was failing with: >>> >>> qemu-img: Could not open 'top.qcow2': Could not open backing file: >>> Failed to get shared "write" lock >>> Is another process using the image [base.qcow2]? >>> >>> The easiest fix is to not open the entire backing chain of either >>> image (source or destination); after all, the point of 'qemu-img >>> bitmap' is solely to manipulate bitmaps directly within a single qcow2 >>> image, and this is made more precise if we don't pay attention to >>> other images in the chain that may happen to have a bitmap by the same >>> name. >>> >>> However, note that during normal usage, it is a feature that qemu will >>> allow a bitmap from a backing image to be exposed by an overlay BDS; >>> doing so makes it easier to perform incremental backup, where we have: >>> >>> Base <- Active <- temporrary >> >> *temporary >> >> (Also it=E2=80=99s a bit strange that =E2=80=9CBase=E2=80=9D and =E2=80= =9CActive=E2=80=9D are capitalized, but >> =E2=80=9Ctemporary=E2=80=9D isn=E2=80=99t) >> >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 \--block j= ob ->/ >>> >>> with temporary being fed by a block-copy 'sync' job; when exposing >> >> s/block-copy 'sync'/backup 'sync=3Dnone'/? >=20 > Will fix both. >=20 >> >>> temporary over NBD, referring to a bitmap that lives only in Active is >>> less effort than having to copy a bitmap into temporary [1].=C2=A0 So t= he >>> testsuite additions in this patch check both where bitmaps get >>> allocated (the qemu-img info output), and, when NOT using 'qemu-img >>> bitmap', that bitmaps are indeed visible through a backing chain. >> >> Well.=C2=A0 It is useful over NBD but I would doubt that it isn=E2=80=99= t useful in >> general.=C2=A0 For example, the QMP commands that refer to bitmaps alway= s do >> so through a node-name + bitmap-name combination, and they require that >> the given bitmap is exactly on the given node. >> >> So I think this is a very much a case-by-case question.=C2=A0 (And in >> practice, NBD seems to be the outlier, not qemu-img bitmap.) >> >=20 > I'm happy to reword slightly to give that caveat. >=20 >>> [1] Full disclosure: prior to the recent commit 374eedd1c4 and >>> friends, we were NOT able to see bitmaps through filters, which meant >>> that we actually did not have nice clean semantics for uniformly being >>> able to pick up bitmaps from anywhere in the backing chain (seen as a >>> change in behavior between qemu 4.1 and 4.2 at commit 00e30f05de, when >>> block-copy swapped from a one-off to a filter).=C2=A0 Which means libvi= rt >>> was already coded to copy bitmaps around for the sake of older qemu, >>> even though modern qemu no longer needs it.=C2=A0 Oh well. >>> >>> Fixes: http://bugzilla.redhat.com/1877209 >>> Reported-by: Eyal Shenitzky >>> Signed-off-by: Eric Blake >>> --- >>> >>> In v2: >>> - also use BDRV_O_NO_BACKING on source [Max] >>> - improved commit message [Max] >>> >>> =C2=A0 qemu-img.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 11 ++++++-- >>> =C2=A0 tests/qemu-iotests/291=C2=A0=C2=A0=C2=A0=C2=A0 | 12 ++++++++ >>> =C2=A0 tests/qemu-iotests/291.out | 56 ++++++++++++++++++++++++++++++++= ++++++ >>> =C2=A0 3 files changed, 76 insertions(+), 3 deletions(-) >> >> The code looks good to me, but I wonder whether in the commit message it >> should be noted that we don=E2=80=99t want to let bitmaps from deeper no= des >> shine through by default everywhere, but just in specific cases where >> that=E2=80=99s useful (i.e. only NBD so far AFAIA). >=20 > So is this a Reviewed-by?=C2=A0 I'm happy to queue it through my bitmaps > tree, if so. It wasn=E2=80=99t meant as an R-b, because my R-b depends on how the commit message addresses the question of when exactly bitmaps from the backing chain should be visible on the top image. Whether qemu-img bitmap is an exception, or whether this is really a case-by-case question. (I wanted to know whether you agree on including it. Normally, I=E2=80=99m happy to give an R-b on the basis of =E2=80=9Cwith that done=E2=80=9D, but = in this case I wasn=E2=80=99t entirely sure whether my request was reasonable, but I als= o felt that in case it was, it wasn=E2=80=99t optional, given that you do hav= e an entire paragraph in the commit message dedicated to why the backing image=E2=80=99s bitmap is visible on an image exported over NBD.) I have to say I would like to see how you do phrase it in the end, but given that you do agree on including it, I can give a Reviewed-by: Max Reitz Now. --h9SGduBELzdgVLvEONw1T4EYz9rlfxoY6-- --E8pNq7L9f6QaDJP8JNi3cux5srbrnOdgm Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl9jOCsACgkQ9AfbAGHV z0Dzlgf+ORL5BZQNJEYqbclvEHCMonMEl/gC2Vhy/jNNKSVFX6CXnBq09eBRHvQs 3GL2lDKJIdX18xhBxLIei55E+fjCZTybaJmk9n/9lNpveDDdbQKMQPglmvzbZUYP FbP0I9IM+/frtqhFIJHIZgG9Skz7zMRR7SXoOh8uStldsj7fQ64zp1AGT7fDzwnP hID6eclFOqwG2rzFCdco0M9zekK3Gcx/p7f9ACFf0AmelH5rDIx4fwVwGCp1U6To piUtetPTtdpXLpDEMWvNYH3A3+UYQqSacVi5XZ0QmWe4k4s7NPeLYksk2t2HcvXD ZVftoUf8g5Bcza88lKiFvekbW+cHXw== =xPuE -----END PGP SIGNATURE----- --E8pNq7L9f6QaDJP8JNi3cux5srbrnOdgm--