From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D303DCA6002 for ; Wed, 7 Oct 2026 16:36:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xEUcp-0004xr-UQ; Wed, 07 Oct 2026 12:36:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xEUbX-00030V-3q for qemu-devel@nongnu.org; Wed, 07 Oct 2026 12:34:58 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xEUbT-0006Nr-MB for qemu-devel@nongnu.org; Wed, 07 Oct 2026 12:34:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791390889; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QGsZ5bbOV1gR0rGL3bdM0NNsq7wL7ymKlhbdLdCIB5M=; b=FEoXTwm5JM5OV+bo1LOTVccGm/1JXTar9m5JSbCyKe6Ha6DMa1ZvBehy9WaoDKkdJc/1cg +6yQY5W9ONziOz/DPd8ucxSY4qa+25pNO9hfn4LNZgEX7NQAH33qX+A/9hj+V/KQM3EWL/ fV2xKKU62MZVBHQh7UsjvpedVWVJG1M= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-251-ThguH2GcM8qhoS6tC97nFA-1; Wed, 07 Oct 2026 12:34:47 -0400 X-MC-Unique: ThguH2GcM8qhoS6tC97nFA-1 X-Mimecast-MFC-AGG-ID: ThguH2GcM8qhoS6tC97nFA_1791390886 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8D5891977010; Wed, 7 Oct 2026 16:34:46 +0000 (UTC) Received: from merkur.redhat.com (unknown [10.44.32.219]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 753831956087; Wed, 7 Oct 2026 16:34:44 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, richard.henderson@linaro.org, qemu-devel@nongnu.org Subject: [PULL 18/21] qcow2: do not clear the dirty bit when reopening a read-only node Date: Wed, 7 Oct 2026 18:32:59 +0200 Message-ID: <20261007163302.332250-19-kwolf@redhat.com> In-Reply-To: <20261007163302.332250-1-kwolf@redhat.com> References: <20261007163302.332250-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 10 X-Spam_score: 1.0 X-Spam_bar: + X-Spam_report: (1.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, 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_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: "Denis V. Lunev" qcow2_reopen_prepare() clears the dirty bit whenever the node is reopened read-only, with an unguarded header write. A read-only node can still be dirty, inherited from an earlier writable session, and it holds no BLK_PERM_WRITE to resolve that. A read-only to read-only reopen of a dirty image therefore fails outright: $ qemu-io -r -f qcow2 dirty.qcow2 <<< $'reopen -r\nquit' qemu-io: failed while preparing to reopen image 'dirty.qcow2' Where the file node below is writable the write is not refused early, and bdrv_co_write_req_prepare() aborts on its BLK_PERM_WRITE assertion instead. Clear it only for a node that is writable now, the predicate qcow2_do_open() already uses for the repair. bdrv_is_writable() also excludes an inactive node, whose header must not be touched either. Signed-off-by: Denis V. Lunev Reviewed-by: Andrey Drobyshev CC: Kevin Wolf CC: Hanna Reitz CC: Andrey Drobyshev Cc: qemu-stable@nongnu.org Message-ID: <20260824133729.1141990-2-den@openvz.org> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- block/qcow2.c | 8 +++--- tests/qemu-iotests/039 | 50 ++++++++++++++++++++++++++++++++++++++ tests/qemu-iotests/039.out | 20 +++++++++++++++ 3 files changed, 75 insertions(+), 3 deletions(-) diff --git a/block/qcow2.c b/block/qcow2.c index 7292dd036c9..1543255eba8 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2102,9 +2102,11 @@ qcow2_reopen_prepare(BDRVReopenState *state,BlockReopenQueue *queue, goto fail; } - ret = qcow2_mark_clean(state->bs); - if (ret < 0) { - goto fail; + if (bdrv_is_writable(state->bs)) { + ret = qcow2_mark_clean(state->bs); + if (ret < 0) { + goto fail; + } } } diff --git a/tests/qemu-iotests/039 b/tests/qemu-iotests/039 index 8fe677ce731..686c6da50fd 100755 --- a/tests/qemu-iotests/039 +++ b/tests/qemu-iotests/039 @@ -93,6 +93,40 @@ $QEMU_IMG info --image-opts \ # The dirty bit must still be set: this open never wrote any guest data _qcow2_dump_header | grep incompatible_features +echo +echo "== Read-only reopen must not clear the dirty bit ==" + +# A read-only node cannot write the header, and must keep the dirty bit +$QEMU_IO -r -c "reopen -r" -c "read -P 0x5a 0 512" "$TEST_IMG" \ + | _filter_qemu_io + +# The dirty bit must still be set +_qcow2_dump_header | grep incompatible_features + +echo +echo "== Read-only reopen must not write through a writable file node ==" + +# The write the header update needs is refused by the permission system +echo "{'execute': 'qmp_capabilities'} + {'execute': 'blockdev-reopen', + 'arguments': {'options': [{'node-name': 'drive', + 'driver': 'qcow2', + 'read-only': true, + 'file': 'prot'}]}} + {'execute': 'quit'}" \ + | $QEMU -qmp stdio -nographic -nodefaults \ + -blockdev "{'node-name': 'prot', + 'driver': 'file', + 'filename': '$TEST_IMG'}" \ + -blockdev "{'node-name': 'drive', + 'driver': 'qcow2', + 'file': 'prot', + 'read-only': true}" \ + | _filter_qmp + +# The dirty bit must still be set +_qcow2_dump_header | grep incompatible_features + echo echo "== Repairing the image file must succeed ==" @@ -106,6 +140,22 @@ echo "== Data should still be accessible after repair ==" $QEMU_IO -c "read -P 0x5a 0 512" "$TEST_IMG" | _filter_qemu_io +echo +echo "== A read-write to read-only reopen must clear the dirty bit ==" + +_make_test_img -o "compat=1.1,lazy_refcounts=on" $size + +# The kill keeps the close from clearing the bit, so the header shows what +# the reopen did with it +_NO_VALGRIND \ +$QEMU_IO -c "write -P 0x5a 0 512" \ + -c "reopen -r" \ + -c "sigraise $(kill -l KILL)" "$TEST_IMG" 2>&1 \ + | _filter_qemu_io + +# The dirty bit must not be set +_qcow2_dump_header | grep incompatible_features + echo echo "== Opening a dirty image read/write should repair it ==" diff --git a/tests/qemu-iotests/039.out b/tests/qemu-iotests/039.out index c66361128f6..ce8ee577216 100644 --- a/tests/qemu-iotests/039.out +++ b/tests/qemu-iotests/039.out @@ -27,6 +27,19 @@ incompatible_features [0] == Read-only open must not crash on close == incompatible_features [0] +== Read-only reopen must not clear the dirty bit == +read 512/512 bytes at offset 0 +512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +incompatible_features [0] + +== Read-only reopen must not write through a writable file node == +QMP_VERSION +{"return": {}} +{"return": {}} +{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}} +{"return": {}} +incompatible_features [0] + == Repairing the image file must succeed == ERROR cluster 5 refcount=0 reference=1 Rebuilding refcount structure @@ -45,6 +58,13 @@ incompatible_features [] read 512/512 bytes at offset 0 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +== A read-write to read-only reopen must clear the dirty bit == +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 +wrote 512/512 bytes at offset 0 +512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +./common.rc: Killed ( VALGRIND_QEMU="${VALGRIND_QEMU_IO}" _qemu_proc_exec "${VALGRIND_LOGFILE}" "$QEMU_IO_PROG" $QEMU_IO_ARGS "$@" ) +incompatible_features [] + == Opening a dirty image read/write should repair it == Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 wrote 512/512 bytes at offset 0 -- 2.56.0