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[PATCH v5 11/16] block: introduce snapshot-access block driver
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
[PATCH v5 11/16] block: introduce snapshot-access block driver |
Date: |
Mon, 28 Feb 2022 12:39:22 +0100 |
The new block driver simply utilizes snapshot-access API of underlying
block node.
In further patches we want to use it like this:
[guest] [NBD export]
| |
| root | root
v file v
[copy-before-write]<------[snapshot-access]
| |
| file | target
v v
[active-disk] [temp.img]
This way, NBD client will be able to read snapshotted state of active
disk, when active disk is continued to be written by guest. This is
known as "fleecing", and currently uses another scheme based on qcow2
temporary image which backing file is active-disk. New scheme comes
with benefits - see next commit.
The other possible application is exporting internal snapshots of
qcow2, like this:
[guest] [NBD export]
| |
| root | root
v file v
[qcow2]<---------[snapshot-access]
For this, we'll need to implement snapshot-access API handlers in
qcow2 driver, and improve snapshot-access block driver (and API) to
make it possible to select snapshot by name. Another thing to improve
is size of snapshot. Now for simplicity we just use size of bs->file,
which is OK for backup, but for qcow2 snapshots export we'll need to
imporve snapshot-access API to get size of snapshot.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
qapi/block-core.json | 4 +-
block/snapshot-access.c | 132 ++++++++++++++++++++++++++++++++++++++++
MAINTAINERS | 1 +
block/meson.build | 1 +
4 files changed, 137 insertions(+), 1 deletion(-)
create mode 100644 block/snapshot-access.c
diff --git a/qapi/block-core.json b/qapi/block-core.json
index ffb7aea2a5..f13b5ff942 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2914,13 +2914,14 @@
# @blkreplay: Since 4.2
# @compress: Since 5.0
# @copy-before-write: Since 6.2
+# @snapshot-access: Since 7.0
#
# Since: 2.9
##
{ 'enum': 'BlockdevDriver',
'data': [ 'blkdebug', 'blklogwrites', 'blkreplay', 'blkverify', 'bochs',
'cloop', 'compress', 'copy-before-write', 'copy-on-read', 'dmg',
- 'file', 'ftp', 'ftps', 'gluster',
+ 'file', 'snapshot-access', 'ftp', 'ftps', 'gluster',
{'name': 'host_cdrom', 'if': 'HAVE_HOST_BLOCK_DEVICE' },
{'name': 'host_device', 'if': 'HAVE_HOST_BLOCK_DEVICE' },
'http', 'https', 'iscsi',
@@ -4267,6 +4268,7 @@
'rbd': 'BlockdevOptionsRbd',
'replication': { 'type': 'BlockdevOptionsReplication',
'if': 'CONFIG_REPLICATION' },
+ 'snapshot-access': 'BlockdevOptionsGenericFormat',
'ssh': 'BlockdevOptionsSsh',
'throttle': 'BlockdevOptionsThrottle',
'vdi': 'BlockdevOptionsGenericFormat',
diff --git a/block/snapshot-access.c b/block/snapshot-access.c
new file mode 100644
index 0000000000..77b87c1946
--- /dev/null
+++ b/block/snapshot-access.c
@@ -0,0 +1,132 @@
+/*
+ * snapshot_access block driver
+ *
+ * Copyright (c) 2022 Virtuozzo International GmbH.
+ *
+ * Author:
+ * Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+
+#include "sysemu/block-backend.h"
+#include "qemu/cutils.h"
+#include "block/block_int.h"
+
+static coroutine_fn int
+snapshot_access_co_preadv_part(BlockDriverState *bs,
+ int64_t offset, int64_t bytes,
+ QEMUIOVector *qiov, size_t qiov_offset,
+ BdrvRequestFlags flags)
+{
+ if (flags) {
+ return -ENOTSUP;
+ }
+
+ return bdrv_co_preadv_snapshot(bs->file, offset, bytes, qiov, qiov_offset);
+}
+
+static int coroutine_fn
+snapshot_access_co_block_status(BlockDriverState *bs,
+ bool want_zero, int64_t offset,
+ int64_t bytes, int64_t *pnum,
+ int64_t *map, BlockDriverState **file)
+{
+ return bdrv_co_snapshot_block_status(bs->file->bs, want_zero, offset,
+ bytes, pnum, map, file);
+}
+
+static int coroutine_fn snapshot_access_co_pdiscard(BlockDriverState *bs,
+ int64_t offset, int64_t bytes)
+{
+ return bdrv_co_pdiscard_snapshot(bs->file->bs, offset, bytes);
+}
+
+static int coroutine_fn
+snapshot_access_co_pwrite_zeroes(BlockDriverState *bs,
+ int64_t offset, int64_t bytes,
+ BdrvRequestFlags flags)
+{
+ return -ENOTSUP;
+}
+
+static coroutine_fn int
+snapshot_access_co_pwritev_part(BlockDriverState *bs,
+ int64_t offset, int64_t bytes,
+ QEMUIOVector *qiov, size_t qiov_offset,
+ BdrvRequestFlags flags)
+{
+ return -ENOTSUP;
+}
+
+
+static void snapshot_access_refresh_filename(BlockDriverState *bs)
+{
+ pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
+ bs->file->bs->filename);
+}
+
+static int snapshot_access_open(BlockDriverState *bs, QDict *options, int
flags,
+ Error **errp)
+{
+ bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+ BDRV_CHILD_DATA | BDRV_CHILD_PRIMARY,
+ false, errp);
+ if (!bs->file) {
+ return -EINVAL;
+ }
+
+ bs->total_sectors = bs->file->bs->total_sectors;
+
+ return 0;
+}
+
+static void snapshot_access_child_perm(BlockDriverState *bs, BdrvChild *c,
+ BdrvChildRole role,
+ BlockReopenQueue *reopen_queue,
+ uint64_t perm, uint64_t shared,
+ uint64_t *nperm, uint64_t *nshared)
+{
+ /*
+ * Currently, we don't need any permissions. If bs->file provides
+ * snapshot-access API, we can use it.
+ */
+ *nperm = 0;
+ *nshared = BLK_PERM_ALL;
+}
+
+BlockDriver bdrv_snapshot_access_drv = {
+ .format_name = "snapshot-access",
+
+ .bdrv_open = snapshot_access_open,
+
+ .bdrv_co_preadv_part = snapshot_access_co_preadv_part,
+ .bdrv_co_pwritev_part = snapshot_access_co_pwritev_part,
+ .bdrv_co_pwrite_zeroes = snapshot_access_co_pwrite_zeroes,
+ .bdrv_co_pdiscard = snapshot_access_co_pdiscard,
+ .bdrv_co_block_status = snapshot_access_co_block_status,
+
+ .bdrv_refresh_filename = snapshot_access_refresh_filename,
+
+ .bdrv_child_perm = snapshot_access_child_perm,
+};
+
+static void snapshot_access_init(void)
+{
+ bdrv_register(&bdrv_snapshot_access_drv);
+}
+
+block_init(snapshot_access_init);
diff --git a/MAINTAINERS b/MAINTAINERS
index 34a36affff..1ccc546cc6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2520,6 +2520,7 @@ F: block/reqlist.c
F: include/block/reqlist.h
F: block/copy-before-write.h
F: block/copy-before-write.c
+F: block/snapshot-access.c
F: include/block/aio_task.h
F: block/aio_task.c
F: util/qemu-co-shared-resource.c
diff --git a/block/meson.build b/block/meson.build
index 41e9cc5dc3..038a95689b 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -34,6 +34,7 @@ block_ss.add(files(
'raw-format.c',
'reqlist.c',
'snapshot.c',
+ 'snapshot-access.c',
'throttle-groups.c',
'throttle.c',
'vhdx-endian.c',
--
2.31.1
- [PATCH v5 00/16] Make image fleecing more usable, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 01/16] block/block-copy: move copy_bitmap initialization to block_copy_state_new(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 02/16] block/dirty-bitmap: bdrv_merge_dirty_bitmap(): add return value, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 04/16] block/copy-before-write: add bitmap open parameter, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 05/16] block/block-copy: add block_copy_reset(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 06/16] block: intoduce reqlist, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 07/16] block/reqlist: reqlist_find_conflict(): use ranges_overlap(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 03/16] block/block-copy: block_copy_state_new(): add bitmap parameter, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 10/16] block/io: introduce block driver snapshot-access API, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 08/16] block/dirty-bitmap: introduce bdrv_dirty_bitmap_status(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 11/16] block: introduce snapshot-access block driver,
Vladimir Sementsov-Ogievskiy <=
- [PATCH v5 09/16] block/reqlist: add reqlist_wait_all(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 12/16] block: copy-before-write: realize snapshot-access API, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 13/16] iotests/image-fleecing: add test-case for fleecing format node, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 14/16] iotests.py: add qemu_io_pipe_and_status(), Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 15/16] iotests/image-fleecing: add test case with bitmap, Vladimir Sementsov-Ogievskiy, 2022/02/28
- [PATCH v5 16/16] iotests/image-fleecing: test push backup with fleecing, Vladimir Sementsov-Ogievskiy, 2022/02/28