{"id":813521,"url":"http://patchwork.ozlabs.org/api/patches/813521/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20170913160333.23622-16-eblake@redhat.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20170913160333.23622-16-eblake@redhat.com>","list_archive_url":null,"date":"2017-09-13T16:03:25","name":"[v4,15/23] qemu-img: Add find_nonzero()","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"aaa36e793815c260035d751ae8a60cea9505f234","submitter":{"id":6591,"url":"http://patchwork.ozlabs.org/api/people/6591/?format=json","name":"Eric Blake","email":"eblake@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20170913160333.23622-16-eblake@redhat.com/mbox/","series":[{"id":2944,"url":"http://patchwork.ozlabs.org/api/series/2944/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=2944","date":"2017-09-13T16:03:10","name":"make bdrv_get_block_status byte-based","version":4,"mbox":"http://patchwork.ozlabs.org/series/2944/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/813521/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/813521/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@bilbo.ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=pass (mailfrom) smtp.mailfrom=nongnu.org\n\t(client-ip=208.118.235.17; helo=lists.gnu.org;\n\tenvelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n\treceiver=)","ext-mx08.extmail.prod.ext.phx2.redhat.com;\n\tdmarc=none (p=none dis=none) header.from=redhat.com","ext-mx08.extmail.prod.ext.phx2.redhat.com;\n\tspf=fail smtp.mailfrom=eblake@redhat.com"],"Received":["from lists.gnu.org (lists.gnu.org [208.118.235.17])\n\t(using TLSv1 with cipher AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3xsmyD3DnVz9s72\n\tfor ;\n\tThu, 14 Sep 2017 02:16:52 +1000 (AEST)","from localhost ([::1]:43420 helo=lists.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.71) (envelope-from\n\t)\n\tid 1dsALK-00073V-Bj\n\tfor incoming@patchwork.ozlabs.org; Wed, 13 Sep 2017 12:16:50 -0400","from eggs.gnu.org ([2001:4830:134:3::10]:45992)\n\tby lists.gnu.org with esmtp (Exim 4.71)\n\t(envelope-from ) id 1dsA9c-0001xg-SZ\n\tfor qemu-devel@nongnu.org; Wed, 13 Sep 2017 12:04:45 -0400","from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)\n\t(envelope-from ) id 1dsA9b-0006LV-RF\n\tfor qemu-devel@nongnu.org; Wed, 13 Sep 2017 12:04:44 -0400","from mx1.redhat.com ([209.132.183.28]:33518)\n\tby eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32)\n\t(Exim 4.71) (envelope-from )\n\tid 1dsA9X-0006HQ-5F; Wed, 13 Sep 2017 12:04:39 -0400","from smtp.corp.redhat.com\n\t(int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11])\n\t(using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby mx1.redhat.com (Postfix) with ESMTPS id 3D592C0587F7;\n\tWed, 13 Sep 2017 16:04:38 +0000 (UTC)","from red.redhat.com (ovpn-120-201.rdu2.redhat.com [10.10.120.201])\n\tby smtp.corp.redhat.com (Postfix) with ESMTP id 08AF869FCA;\n\tWed, 13 Sep 2017 16:04:36 +0000 (UTC)"],"DMARC-Filter":"OpenDMARC Filter v1.3.2 mx1.redhat.com 3D592C0587F7","From":"Eric Blake ","To":"qemu-devel@nongnu.org","Date":"Wed, 13 Sep 2017 11:03:25 -0500","Message-Id":"<20170913160333.23622-16-eblake@redhat.com>","In-Reply-To":"<20170913160333.23622-1-eblake@redhat.com>","References":"<20170913160333.23622-1-eblake@redhat.com>","X-Scanned-By":"MIMEDefang 2.79 on 10.5.11.11","X-Greylist":"Sender IP whitelisted, not delayed by milter-greylist-4.5.16\n\t(mx1.redhat.com [10.5.110.32]);\n\tWed, 13 Sep 2017 16:04:38 +0000 (UTC)","X-detected-operating-system":"by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic]\n\t[fuzzy]","X-Received-From":"209.132.183.28","Subject":"[Qemu-devel] [PATCH v4 15/23] qemu-img: Add find_nonzero()","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.21","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Cc":"kwolf@redhat.com, jsnow@redhat.com, famz@redhat.com,\n\tqemu-block@nongnu.org, Max Reitz ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"\"Qemu-devel\"\n\t"},"content":"During 'qemu-img compare', when we are checking that an allocated\nportion of one file is all zeros, we don't need to waste time\ncomputing how many additional sectors after the first non-zero\nbyte are also non-zero. Create a new helper find_nonzero() to do\nthe check for a first non-zero sector, and rebase\ncheck_empty_sectors() to use it.\n\nThe new interface intentionally uses bytes in its interface, even\nthough it still crawls the buffer a sector at a time; it is robust\nto a partial sector at the end of the buffer.\n\nSigned-off-by: Eric Blake \n\n---\nv3: new patch\n---\n qemu-img.c | 32 ++++++++++++++++++++++++++++----\n 1 file changed, 28 insertions(+), 4 deletions(-)","diff":"diff --git a/qemu-img.c b/qemu-img.c\nindex f5ab29d176..dfccebe6bc 100644\n--- a/qemu-img.c\n+++ b/qemu-img.c\n@@ -1064,6 +1064,28 @@ done:\n }\n\n /*\n+ * Returns -1 if 'buf' contains only zeroes, otherwise the byte index\n+ * of the first sector boundary within buf where the sector contains a\n+ * non-zero byte. This function is robust to a buffer that is not\n+ * sector-aligned.\n+ */\n+static int64_t find_nonzero(const uint8_t *buf, int64_t n)\n+{\n+ int64_t i;\n+ int64_t end = QEMU_ALIGN_DOWN(n, BDRV_SECTOR_SIZE);\n+\n+ for (i = 0; i < end; i += BDRV_SECTOR_SIZE) {\n+ if (!buffer_is_zero(buf + i, BDRV_SECTOR_SIZE)) {\n+ return i;\n+ }\n+ }\n+ if (i < n && !buffer_is_zero(buf + i, n - end)) {\n+ return i;\n+ }\n+ return -1;\n+}\n+\n+/*\n * Returns true iff the first sector pointed to by 'buf' contains at least\n * a non-NUL byte.\n *\n@@ -1188,7 +1210,9 @@ static int check_empty_sectors(BlockBackend *blk, int64_t sect_num,\n int sect_count, const char *filename,\n uint8_t *buffer, bool quiet)\n {\n- int pnum, ret = 0;\n+ int ret = 0;\n+ int64_t idx;\n+\n ret = blk_pread(blk, sect_num << BDRV_SECTOR_BITS, buffer,\n sect_count << BDRV_SECTOR_BITS);\n if (ret < 0) {\n@@ -1196,10 +1220,10 @@ static int check_empty_sectors(BlockBackend *blk, int64_t sect_num,\n sectors_to_bytes(sect_num), filename, strerror(-ret));\n return ret;\n }\n- ret = is_allocated_sectors(buffer, sect_count, &pnum);\n- if (ret || pnum != sect_count) {\n+ idx = find_nonzero(buffer, sect_count * BDRV_SECTOR_SIZE);\n+ if (idx >= 0) {\n qprintf(quiet, \"Content mismatch at offset %\" PRId64 \"!\\n\",\n- sectors_to_bytes(ret ? sect_num : sect_num + pnum));\n+ sectors_to_bytes(sect_num) + idx);\n return 1;\n }\n\n","prefixes":["v4","15/23"]}