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Tue, 07 Jul 2020 10:46:46 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-513-hGipqnMGMciNUEmyxoNk1Q-1; Tue, 07 Jul 2020 10:46:38 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E69941005510; Tue, 7 Jul 2020 14:46:36 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-114-113.ams2.redhat.com [10.36.114.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id D1D5F5C1B2; Tue, 7 Jul 2020 14:46:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594133199; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=8uRqbq9+MGzTzxMr5ja7NLIkCymq/NQVdrEfBxzsaNI=; b=W324qQbHVPQrPVPfNx+m5RZl4deiWjCGxHTbZ7ad8qfjE/1zpKFoSRn6QGvRcBDsPEES4f 3QRV2SdIX1iHpdmXMmcASp2wIAv4O7zn+m0gigKAbndjZMZP0oxwxwBwwB0/9mt2foq5iL 32RcU8MPaoFp37ZvtnjUl6XKFMw2fD8= X-MC-Unique: hGipqnMGMciNUEmyxoNk1Q-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH] qemu-img map: Don't limit block status request size Date: Tue, 7 Jul 2020 16:46:29 +0200 Message-Id: <20200707144629.51235-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=207.211.31.81; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 00:20:54 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @redhat.com) Content-Type: text/plain; charset="utf-8" Limiting each loop iteration of qemu-img map to 1 GB was arbitrary from the beginning, though it only cut the maximum in half then because the interface a signed 32 bit byte count. These days, bdrv_block_status() supports a 64 bit byte count, so the arbitrary limit is even worse. On file-posix, bdrv_block_status() eventually maps to SEEK_HOLE and SEEK_DATA, which don't support a limit, but always do all of the work necessary to find the start of the next hole/data. Much of this work may be repeated if we don't use this information fully, but query with an only slightly larger offset in the next loop iteration. Therefore, if bdrv_block_status() is called in a loop, it should always pass the full number of bytes that the whole loop is interested in. This removes the arbitrary limit and speeds up 'qemu-img map' significantly on heavily fragmented images. Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake --- qemu-img.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index bdb9f6aa46..74946f81ca 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3217,12 +3217,9 @@ static int img_map(int argc, char **argv) curr.start =3D start_offset; while (curr.start + curr.length < length) { int64_t offset =3D curr.start + curr.length; - int64_t n; + int64_t n =3D length - offset; =20 - /* Probe up to 1 GiB at a time. */ - n =3D MIN(1 * GiB, length - offset); ret =3D get_block_status(bs, offset, n, &next); - if (ret < 0) { error_report("Could not read file metadata: %s", strerror(-ret= )); goto out; --=20 2.25.4