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(No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AEA3220F2; Tue, 1 Oct 2019 16:07:57 +0000 (UTC) Received: from [10.10.120.126] (ovpn-120-126.rdu2.redhat.com [10.10.120.126]) by smtp.corp.redhat.com (Postfix) with ESMTP id E98EB5D9E1; Tue, 1 Oct 2019 16:07:55 +0000 (UTC) Subject: Re: bitmap migration bug with -drive while block mirror runs To: Vladimir Sementsov-Ogievskiy References: <315cff78-dcdb-a3ce-2742-da3cc9f0ca97@redhat.com> <4bc910ef-0bec-cfd6-89f6-a93d35367218@redhat.com> <9431d242-bfe1-b9db-17d0-6c1a280a05da@virtuozzo.com> From: John Snow Autocrypt: addr=jsnow@redhat.com; prefer-encrypt=mutual; keydata= mQINBFTKefwBEAChvwqYC6saTzawbih87LqBYq0d5A8jXYXaiFMV/EvMSDqqY4EY6whXliNO IYzhgrPEe7ZmPxbCSe4iMykjhwMh5byIHDoPGDU+FsQty2KXuoxto+ZdrP9gymAgmyqdk3aV vzzmCa3cOppcqKvA0Kqr10UeX/z4OMVV390V+DVWUvzXpda45/Sxup57pk+hyY52wxxjIqef rj8u5BN93s5uCVTus0oiVA6W+iXYzTvVDStMFVqnTxSxlpZoH5RGKvmoWV3uutByQyBPHW2U 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List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Krempa , qemu-devel , Qemu-block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/1/19 11:57 AM, Vladimir Sementsov-Ogievskiy wrote: > 01.10.2019 17:10, John Snow wrote: >> >> >> On 10/1/19 10:00 AM, Vladimir Sementsov-Ogievskiy wrote: >>>> 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 for >>>> the node the bitmap is attached to, which would be the name of the first >>>> ancestor node that isn't a filter. (OR, the name of the block-backend >>>> above that node.) >>> Not the name of ancestor node, it will break mapping: it must be name of the >>> node itself or name of parent (may be through several filters) block-backend >>> >> >> Ah, you are right of course -- because block-backends are the only >> "nodes" for which we actually descend the graph and add the bitmap to >> its child. >> >> So the real back-resolution mechanism is: >> Amendment: - If our local node-name N is well-formed, use this. - Otherwise: >> - Find the first non-filter ancestor, A >> - if A is not a block-backend, we must use our node-local name. Amendment: If it's not a BB, we have no addressable name for the bitmap and this is an error. >> - if A's name is empty, we must use our node-local name. Amendment: If it's empty, we have no addressable name for the bitmap and this is an error. >> - If the name we have chosen is not id_wellformed, we have no >> migration-stable addressable name for this bitmap and the migration must >> fail! (Handled by above amendments.) The reason for the change is to prefer user-defined node names whenever possible; only trying to find a "device" or "backend" name whenever we fail to find one. >> >> >> For resolving bitmap addresses via QMP (node, name) pairs; the >> resolution method would be this: >> >> - if the node-name N is a block-backend, descend the tree until we find >> the first non-filter node V. >> - if the node-name N is a BlockDriverState, use this node directly. >> > > Looks good for me. > I hope the increased leeway of the name resolution doesn't make things worse with respect to filters. I specified this to match the back-resolution process. I suppose if you want to add bitmaps to filters, you are required to add them by node-name specifically. > I also think if on destination we have both block-backend with name N and > block-node with name N and the latter is not (filtered) child of the former, > we should fail migration of at least that bitmap. (Hope, nobody reuse > block-backend names as node-names in practice.. (should we restrict it > explicitly ?)) > :( >> >> (I don't have the time to investigate the code snippet right now; my >> attention is being pulled to a different project. sorry!) >> > > So, you are not working on this? Then I'll make patches. > Right; I'm not prototyping a fix currently. --js