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Tue, 01 Oct 2019 23:47:19 +0000 Received: from b01ledav001.gho.pok.ibm.com (b01ledav001.gho.pok.ibm.com [9.57.199.106]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x91NlIUk48038200 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 1 Oct 2019 23:47:18 GMT Received: from b01ledav001.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 95F0A28060; Tue, 1 Oct 2019 23:47:18 +0000 (GMT) Received: from b01ledav001.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 79CC628059; Tue, 1 Oct 2019 23:47:18 +0000 (GMT) Received: from localhost (unknown [9.53.179.213]) by b01ledav001.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 1 Oct 2019 23:47:18 +0000 (GMT) From: Michael Roth To: qemu-devel@nongnu.org Subject: [PATCH 13/97] block/file-posix: Unaligned O_DIRECT block-status Date: Tue, 1 Oct 2019 18:44:52 -0500 Message-Id: <20191001234616.7825-14-mdroth@linux.vnet.ibm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191001234616.7825-1-mdroth@linux.vnet.ibm.com> References: <20191001234616.7825-1-mdroth@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-10-01_10:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910010203 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.158.5 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 , qemu-stable@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Max Reitz Currently, qemu crashes whenever someone queries the block status of an unaligned image tail of an O_DIRECT image: $ echo > foo $ qemu-img map --image-opts driver=file,filename=foo,cache.direct=on Offset Length Mapped to File qemu-img: block/io.c:2093: bdrv_co_block_status: Assertion `*pnum && QEMU_IS_ALIGNED(*pnum, align) && align > offset - aligned_offset' failed. This is because bdrv_co_block_status() checks that the result returned by the driver's implementation is aligned to the request_alignment, but file-posix can fail to do so, which is actually mentioned in a comment there: "[...] possibly including a partial sector at EOF". Fix this by rounding up those partial sectors. There are two possible alternative fixes: (1) We could refuse to open unaligned image files with O_DIRECT altogether. That sounds reasonable until you realize that qcow2 does necessarily not fill up its metadata clusters, and that nobody runs qemu-img create with O_DIRECT. Therefore, unpreallocated qcow2 files usually have an unaligned image tail. (2) bdrv_co_block_status() could ignore unaligned tails. It actually throws away everything past the EOF already, so that sounds reasonable. Unfortunately, the block layer knows file lengths only with a granularity of BDRV_SECTOR_SIZE, so bdrv_co_block_status() usually would have to guess whether its file length information is inexact or whether the driver is broken. Fixing what raw_co_block_status() returns is the safest thing to do. There seems to be no other block driver that sets request_alignment and does not make sure that it always returns aligned values. Cc: qemu-stable@nongnu.org Signed-off-by: Max Reitz Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf (cherry picked from commit 9c3db310ff0b7473272ae8dce5e04e2f8a825390) Signed-off-by: Michael Roth --- block/file-posix.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index 1cf4ee49eb..c185f34a2e 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2475,6 +2475,8 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs, off_t data = 0, hole = 0; int ret; + assert(QEMU_IS_ALIGNED(offset | bytes, bs->bl.request_alignment)); + ret = fd_open(bs); if (ret < 0) { return ret; @@ -2500,6 +2502,20 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs, /* On a data extent, compute bytes to the end of the extent, * possibly including a partial sector at EOF. */ *pnum = MIN(bytes, hole - offset); + + /* + * We are not allowed to return partial sectors, though, so + * round up if necessary. + */ + if (!QEMU_IS_ALIGNED(*pnum, bs->bl.request_alignment)) { + int64_t file_length = raw_getlength(bs); + if (file_length > 0) { + /* Ignore errors, this is just a safeguard */ + assert(hole == file_length); + } + *pnum = ROUND_UP(*pnum, bs->bl.request_alignment); + } + ret = BDRV_BLOCK_DATA; } else { /* On a hole, compute bytes to the beginning of the next extent. */ -- 2.17.1