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 lists.gnu.org (unknown [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 B712510F996A for ; Wed, 8 Apr 2026 18:49:00 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wAXvl-0002tJ-Il; Wed, 08 Apr 2026 14:47:13 -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 1wAXvj-0002mq-Pz for qemu-devel@nongnu.org; Wed, 08 Apr 2026 14:47:11 -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 1wAE6a-0001Hh-Cv for qemu-devel@nongnu.org; Tue, 07 Apr 2026 17:37:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1775597823; 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=lLHbJbpbVpCc7ZPDfJzkupfRH4+Vp1i+3Y5xDT7n2Qg=; b=IvPpCY7o2L29JddYotS2sBYW1zLml9YlReuTuURY8b6tKdOFGAGTfB9D/WSTpX6JkUZ/Z6 IYdBSbC9Syj54gtUmMaC2p+tIzHM/H6pooetsdtNpRZEC4jTClBsx2id0UlcK1YD1U7biQ rFxiybk8xmj7+4AaqJgpPhADUmrUkKY= 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-479-lF6QmrMJM8CPq5-BLHxq3A-1; Tue, 07 Apr 2026 17:37:00 -0400 X-MC-Unique: lF6QmrMJM8CPq5-BLHxq3A-1 X-Mimecast-MFC-AGG-ID: lF6QmrMJM8CPq5-BLHxq3A_1775597819 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 4569F1956053; Tue, 7 Apr 2026 21:36:58 +0000 (UTC) Received: from green.redhat.com (unknown [10.2.16.159]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 774A619560A6; Tue, 7 Apr 2026 21:36:56 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org Cc: Vladimir Sementsov-Ogievskiy , Pierrick Bouvier , Kevin Wolf , Hanna Reitz , qemu-block@nongnu.org (open list:Network Block Dev...) Subject: [PATCH] qemu-nbd: Support -s and -l at the same time Date: Tue, 7 Apr 2026 16:36:17 -0500 Message-ID: <20260407213652.769100-2-eblake@redhat.com> MIME-Version: 1.0 Content-type: text/plain 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=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable 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 qemu-nbd already has the ability to wrap a read-write layer on top of the export of a read-only image (-s) and the ability to export an internal snapshot rather than the main image in a qcow2 file (-l SNAPID). But it gave a confusing error message when trying to mix the two, because the snapshot overlay created first no longer has access to the internal snapshots of the image being wrapped. WIth a bit of finesse, this useful scenario is now supported. https://gitlab.com/qemu-project/qemu/-/work_items/159 Signed-off-by: Eric Blake --- docs/tools/qemu-nbd.rst | 7 +- qemu-nbd.c | 20 ++++- tests/qemu-iotests/tests/qemu-nbd-snapshots | 79 +++++++++++++++++++ .../qemu-iotests/tests/qemu-nbd-snapshots.out | 34 ++++++++ 4 files changed, 134 insertions(+), 6 deletions(-) create mode 100755 tests/qemu-iotests/tests/qemu-nbd-snapshots create mode 100644 tests/qemu-iotests/tests/qemu-nbd-snapshots.out diff --git a/docs/tools/qemu-nbd.rst b/docs/tools/qemu-nbd.rst index f82ea5fd77b..336b4aa46e7 100644 --- a/docs/tools/qemu-nbd.rst +++ b/docs/tools/qemu-nbd.rst @@ -95,9 +95,10 @@ driver options if :option:`--image-opts` is specified. .. option:: -l, --load-snapshot=SNAPSHOT_PARAM - Load an internal snapshot inside *filename* and export it - as an read-only device, SNAPSHOT_PARAM format is - ``snapshot.id=[ID],snapshot.name=[NAME]`` or ``[ID_OR_NAME]`` + Load an internal snapshot inside *filename* and export it. + SNAPSHOT_PARAM format is ``snapshot.id=[ID],snapshot.name=[NAME]`` + or ``[ID_OR_NAME]``. The export is read-only unless ``-s`` is also + in use. .. option:: --cache=CACHE diff --git a/qemu-nbd.c b/qemu-nbd.c index ed5895861bb..128486a0ec2 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -534,6 +534,7 @@ int main(int argc, char **argv) { BlockBackend *blk; BlockDriverState *bs; + BlockDriverState *orig_bs; uint64_t dev_offset = 0; bool readonly = false; bool disconnect = false; @@ -716,7 +717,7 @@ int main(int argc, char **argv) } else { sn_id_or_name = optarg; } - /* fall through */ + break; case 'r': readonly = true; flags &= ~BDRV_O_RDWR; @@ -1110,6 +1111,15 @@ int main(int argc, char **argv) bdrv_init(); atexit(qemu_nbd_shutdown); + /* + * -s and -l can be used together to create read-write wrapper + * around an internal snapshot. Otherwise, -l in isolation implies + * read-only. + */ + if ((sn_opts || sn_id_or_name) && (flags & BDRV_O_SNAPSHOT) == 0) { + readonly = true; + flags &= ~BDRV_O_RDWR; + } opts.srcpath = argv[optind]; if (imageOpts) { QemuOpts *o; @@ -1155,13 +1165,17 @@ int main(int argc, char **argv) blk_set_enable_write_cache(blk, !writethrough); + orig_bs = bs; + if (flags & BDRV_O_SNAPSHOT) { + orig_bs = bs->backing->bs; + } if (sn_opts) { - ret = bdrv_snapshot_load_tmp(bs, + ret = bdrv_snapshot_load_tmp(orig_bs, qemu_opt_get(sn_opts, SNAPSHOT_OPT_ID), qemu_opt_get(sn_opts, SNAPSHOT_OPT_NAME), &local_err); } else if (sn_id_or_name) { - ret = bdrv_snapshot_load_tmp_by_id_or_name(bs, sn_id_or_name, + ret = bdrv_snapshot_load_tmp_by_id_or_name(orig_bs, sn_id_or_name, &local_err); } if (ret < 0) { diff --git a/tests/qemu-iotests/tests/qemu-nbd-snapshots b/tests/qemu-iotests/tests/qemu-nbd-snapshots new file mode 100755 index 00000000000..de405e43720 --- /dev/null +++ b/tests/qemu-iotests/tests/qemu-nbd-snapshots @@ -0,0 +1,79 @@ +#!/usr/bin/env bash +# group: rw quick +# +# Test qemu-nbd snapshot handling +# +# Copyright (C) Red Hat, Inc. +# +# SPDX-License-Identifier: GPL-2.0-or-later + +seq="$(basename $0)" +echo "QA output created by $seq" + +status=1 # failure is the default! + +_cleanup() +{ + _cleanup_test_img + nbd_server_stop +} +trap "_cleanup; exit \$status" 0 1 2 3 15 + +# get standard environment, filters and checks +cd .. +. ./common.rc +. ./common.filter +. ./common.nbd + +_supported_fmt qcow2 +_supported_proto file +_supported_os Linux +_require_command QEMU_NBD + +echo +echo "=== Initial image setup ===" +echo + +# Create qcow2 image with one internal snapshot +_make_test_img 10M +$QEMU_IO -c 'w -P 1 3M 1M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io +$QEMU_IMG snapshot -c snap -f $IMGFMT "$TEST_IMG" | _filter_qemu_img +$QEMU_IO -c 'w -P 2 3M 1M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io + +echo +echo "=== Main image in snapshot mode ===" +echo + +nbd_server_start_unix_socket -s -f qcow2 "$TEST_IMG" +$QEMU_IO -c 'r -P 2 3M 1M' -c 'w -P 3 3M 1M' -f raw \ + nbd:unix:$nbd_unix_socket | _filter_qemu_io +nbd_server_stop + +echo +echo "=== Read-only snapshot access ===" +echo + +nbd_server_start_unix_socket -l snap -f qcow2 "$TEST_IMG" +$QEMU_IO -r -c 'r -P 1 3M 1M' -f raw \ + nbd:unix:$nbd_unix_socket | _filter_qemu_io +nbd_server_stop + +echo +echo "=== Combine -s and -l for read-write internal snapshot access ===" +echo + +nbd_server_start_unix_socket -s -l snap -f qcow2 "$TEST_IMG" +$QEMU_IO -c 'r -P 1 3M 1M' -c 'w -P 3 3M 1M' -f raw \ + nbd:unix:$nbd_unix_socket | _filter_qemu_io +nbd_server_stop + +echo +echo "=== Check that original image is unchanged ===" +echo + +$QEMU_IO -c 'r -P 2 3M 1M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io + +# success, all done +echo '*** done' +rm -f $seq.full +status=0 diff --git a/tests/qemu-iotests/tests/qemu-nbd-snapshots.out b/tests/qemu-iotests/tests/qemu-nbd-snapshots.out new file mode 100644 index 00000000000..6bce9d90253 --- /dev/null +++ b/tests/qemu-iotests/tests/qemu-nbd-snapshots.out @@ -0,0 +1,34 @@ +QA output created by qemu-nbd-snapshots + +=== Initial image setup === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=10485760 +wrote 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +wrote 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) + +=== Main image in snapshot mode === + +read 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +wrote 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) + +=== Read-only snapshot access === + +read 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) + +=== Combine -s and -l for read-write internal snapshot access === + +read 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +wrote 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) + +=== Check that original image is unchanged === + +read 1048576/1048576 bytes at offset 3145728 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +*** done -- 2.53.0