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Tue, 1 Oct 2019 14:13:10 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.251]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5FC295D9D5; Tue, 1 Oct 2019 14:13:06 +0000 (UTC) Subject: Re: bitmap migration bug with -drive while block mirror runs To: Vladimir Sementsov-Ogievskiy , John Snow References: <315cff78-dcdb-a3ce-2742-da3cc9f0ca97@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <6dd4e735-47e7-45d1-98e9-2131746d470c@redhat.com> Date: Tue, 1 Oct 2019 16:13:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="oZ7VuI6VUMhDwKX5TMbxc17vU3EVmGrr7" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.62]); Tue, 01 Oct 2019 14:13:10 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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 Krempa , qemu-devel , Qemu-block 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) --oZ7VuI6VUMhDwKX5TMbxc17vU3EVmGrr7 Content-Type: multipart/mixed; boundary="zyv6WEWOGmu44j5vmPQEvn0c6ScwdADBn" --zyv6WEWOGmu44j5vmPQEvn0c6ScwdADBn Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01.10.19 16:00, Vladimir Sementsov-Ogievskiy wrote: > 01.10.2019 3:09, John Snow wrote: >> Hi folks, I identified a problem with the migration code that Red Hat = QE >> found and thought you'd like to see it: >> >> https://bugzilla.redhat.com/show_bug.cgi?id=3D1652424#c20 >> >> Very, very briefly: drive-mirror inserts a filter node that changes wh= at >> bdrv_get_device_or_node_name() returns, which causes a migration probl= em. >> >> >> Ignorant question #1: Can we multi-parent the filter node and >> source-node? It looks like at the moment both consider their only pare= nt >> to be the block-job and don't have a link back to their parents otherw= ise. >> >> >> Otherwise: I have a lot of cloudy ideas on how to solve this, but >> ultimately what we want is to be able to find the "addressable" name f= or >> the node the bitmap is attached to, which would be the name of the fir= st >> ancestor node that isn't a filter. (OR, the name of the block-backend >> above that node.) >=20 > Not the name of ancestor node, it will break mapping: it must be name o= f the > node itself or name of parent (may be through several filters) block-ba= ckend >=20 >> >> A simple way to do this might be a "child_unfiltered" BdrvChild role >> that simply bypasses the filter that was inserted and serves no real >> purpose other than to allow the child to have a parent link and find w= ho >> it's """real""" parent is. >> >> Because of flushing, reopen, sync, drain &c &c &c I'm not sure how >> feasible this quick idea might be, though. >> >> >> - Corollary fix #1: call error_setg if the bitmap node name that's abo= ut >> to go over the wire is an autogenerated node: this is never correct! >> >> (Why not? because the target is incapable of matching the node-name >> because they are randomly generated AND you cannot specify node-names >> with # prefixes as they are especially reserved! >> >> (This raises a related problem: if you explicitly add bitmaps to nodes= >> with autogenerated names, you will be unable to migrate them.)) >> >> --js >> >=20 > What about the following: >=20 > diff --git a/block.c b/block.c > index 5944124845..6739c19be9 100644 > --- a/block.c > +++ b/block.c > @@ -1009,8 +1009,20 @@ static void bdrv_inherited_options(int *child_fl= ags, QDict *child_options, > *child_flags =3D flags; > } >=20 > +static const char *bdrv_child_get_name(BdrvChild *child) > +{ > + BlockDriverState *parent =3D child->opaque; > + > + if (parent->drv && parent->drv->is_filter) { > + return bdrv_get_parent_name(parent); > + } > + > + return NULL; > +} > + Why would we skip filters explicitly added by the user? 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