@@ -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',
@@ -606,6 +606,12 @@ struct BlockDriver {
* in generic block-layer: no serializing, no alignment, no tracked
* requests. So, block-driver that realizes these APIs is fully responsible
* for synchronization between snapshot-access API and normal IO requests.
+ *
+ * TODO: To be able to support qcow2's internal snapshots, this API will
+ * need to be extended to:
+ * - be able to select a specific snapshot
+ * - receive the snapshot's actual length (which may differ from bs's
+ * length)
*/
int coroutine_fn (*bdrv_co_preadv_snapshot)(BlockDriverState *bs,
int64_t offset, int64_t bytes, QEMUIOVector *qiov, size_t qiov_offset);
new file mode 100644
@@ -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);
@@ -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
@@ -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',