From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37164) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bymgg-00012g-Kv for qemu-devel@nongnu.org; Mon, 24 Oct 2016 17:21:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bymgf-0000fp-Gl for qemu-devel@nongnu.org; Mon, 24 Oct 2016 17:21:42 -0400 References: From: Eric Blake Message-ID: <8a8853e4-d1ce-66b2-5214-b508fb897386@redhat.com> Date: Mon, 24 Oct 2016 16:21:33 -0500 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="JqapF1denxOVqpT5wCWJ7a5kigTsR2j0V" Subject: Re: [Qemu-devel] Assertion failure on qcow2 disk with cluster_size != 64k List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ed Swierk , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: Kevin Wolf , "Denis V. Lunev" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --JqapF1denxOVqpT5wCWJ7a5kigTsR2j0V From: Eric Blake To: Ed Swierk , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: Kevin Wolf , "Denis V. Lunev" Message-ID: <8a8853e4-d1ce-66b2-5214-b508fb897386@redhat.com> Subject: Re: [Qemu-devel] Assertion failure on qcow2 disk with cluster_size != 64k References: In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 10/20/2016 07:24 PM, Ed Swierk wrote: > Shortly after I start qemu 2.7.0 with a qcow2 disk image created with > -o cluster_size=3D1048576, it prints the following and dies: >=20 > block/qcow2.c:2451: qcow2_co_pwrite_zeroes: Assertion `head + count <=3D= > s->cluster_size' failed. >=20 > I narrowed the problem to bdrv_co_do_pwrite_zeroes(), called by > bdrv_aligned_pwritev() with flags & BDRV_REQ_ZERO_WRITE set. >=20 > On the first loop iteration, offset=3D8003584, count=3D2093056, > head=3D663552, tail=3D659456 and num=3D2093056. qcow2_co_pwrite_zeroes(= ) is > called with offset=3D8003584 and count=3D385024 and finds that the head= > portion is not already zero, so it returns -ENOTSUP. > bdrv_co_do_pwrite_zeroes() falls back to a normal write, with > max_transfer=3D65536. How are you getting max_transfer =3D=3D 65536? I can't reproduce it with= the following setup: $ qemu-img create -f qcow2 -o cluster_size=3D1M file 10M $ qemu-io -f qcow2 -c 'w 7m 1k' file $ qemu-io -f qcow2 -c 'w -z 8003584 2093056' file although I did confirm that the above sequence was enough to get the -ENOTSUP failure and fall into the code calculating max_transfer. I'm guessing that you are using something other than a file system as the backing protocol for your qcow2 image. But do you really have a protocol that takes AT MOST 64k per transaction, while still trying to a cluster size of 1M in the qcow2 format? That's rather awkward, as it means that you are required to do 16 transactions per cluster (the whole point of using larger clusters is usually to get fewer transactions). I think we need to get to a root cause of why you are seeing such a small max_transfer, before I can propose the right patch, since I haven't been able to reproduce it locally yet (although I admit I haven't tried to see if blkdebug could reliably introduce artificial limits to simulate your setup). And it may turn out that I just have to fix the bdrv_co_do_pwrite_zeroes() code to loop multiple times if the size of the unaligned head really does exceed the max_transfer size that the underlying protocol is able to support, rather than assuming that the unaligned head/tail always fit in a single fallback write. Can you also try this patch? If I'm right, you'll still fail, but the assertion will be slightly different. (Again, I'm passing locally, but that's because I'm using the file protocol, and my file system does not impose a puny 64k max transfer). diff --git i/block/io.c w/block/io.c index b136c89..8757063 100644 --- i/block/io.c +++ w/block/io.c @@ -1179,6 +1179,8 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, int max_write_zeroes =3D MIN_NON_ZERO(bs->bl.max_pwrite_zeroes, INT_= MAX); int alignment =3D MAX(bs->bl.pwrite_zeroes_alignment, bs->bl.request_alignment); + int max_transfer =3D MIN_NON_ZERO(bs->bl.max_transfer, + MAX_WRITE_ZEROES_BOUNCE_BUFFER); assert(alignment % bs->bl.request_alignment =3D=3D 0); head =3D offset % alignment; @@ -1197,6 +1199,8 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, /* Make a small request up to the first aligned sector. */ num =3D MIN(count, alignment - head); head =3D 0; + assert(num < max_write_zeroes); + assert(num < max_transfer); } else if (tail && num > alignment) { /* Shorten the request to the last aligned sector. */ num -=3D tail; @@ -1222,8 +1226,6 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, if (ret =3D=3D -ENOTSUP) { /* Fall back to bounce buffer if write zeroes is unsupported= */ - int max_transfer =3D MIN_NON_ZERO(bs->bl.max_transfer, - MAX_WRITE_ZEROES_BOUNCE_BUFFER); BdrvRequestFlags write_flags =3D flags & ~BDRV_REQ_ZERO_WRIT= E; if ((flags & BDRV_REQ_FUA) && --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --JqapF1denxOVqpT5wCWJ7a5kigTsR2j0V Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJYDntdAAoJEKeha0olJ0Nqzn4H/2pqsgv8YIxWS205TbFCYW5v 7P2JOrkKx/84wMcof34olLpLnfMfJhw65j4IIpU80MaBihMUijyoJmmf+UorsF/g 6gWR3LFqorO8c+dkfBhR6mFKhsTurDeEQ7CHi96osl3gq4p/aSr510tJCGnugDl9 C1yrDdYZtHFOwkCkUP5iQN9KMejJQtZSidSSGvyHFxbzWgIr+K5VNbmPzezsF0wk AbunHORff1wdV2sjMIGMbP3iwPNvdsdBuxO36HZg50dm4v1QMzXGVJxaAiix1f3c /sWXT2guX+jN9HqkzEOq47UrYNRy2Gfgiw/Vx5Hy2usDqyHWv+NNkKMvakTNKMM= =23vj -----END PGP SIGNATURE----- --JqapF1denxOVqpT5wCWJ7a5kigTsR2j0V--