new file mode 100644
@@ -0,0 +1,41 @@
+/*
+ * backup-top filter driver
+ *
+ * The driver performs Copy-Before-Write (CBW) operation: it is injected above
+ * some node, and before each write it copies _old_ data to the target node.
+ *
+ * Copyright (c) 2018-2019 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/>.
+ */
+
+#ifndef BACKUP_TOP_H
+#define BACKUP_TOP_H
+
+#include "block/block_int.h"
+#include "block/block-copy.h"
+
+BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
+ BlockDriverState *target,
+ const char *filter_node_name,
+ uint64_t cluster_size,
+ BdrvRequestFlags write_flags,
+ BlockCopyState **bcs,
+ Error **errp);
+void bdrv_backup_top_drop(BlockDriverState *bs);
+
+#endif /* BACKUP_TOP_H */
new file mode 100644
@@ -0,0 +1,281 @@
+/*
+ * backup-top filter driver
+ *
+ * The driver performs Copy-Before-Write (CBW) operation: it is injected above
+ * some node, and before each write it copies _old_ data to the target node.
+ *
+ * Copyright (c) 2018-2019 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 "qapi/error.h"
+#include "block/block_int.h"
+#include "block/qdict.h"
+#include "block/block-copy.h"
+
+#include "block/backup-top.h"
+
+typedef struct BDRVBackupTopState {
+ BlockCopyState *bcs;
+ BdrvChild *target;
+ bool active;
+} BDRVBackupTopState;
+
+static coroutine_fn int backup_top_co_preadv(
+ BlockDriverState *bs, uint64_t offset, uint64_t bytes,
+ QEMUIOVector *qiov, int flags)
+{
+ return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
+}
+
+static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
+ uint64_t bytes)
+{
+ /*
+ * Here we'd like to use block_copy(), but block-copy need to be moved to
+ * use BdrvChildren to correctly use it in backup-top filter. It's a TODO.
+ */
+
+ abort();
+}
+
+static int coroutine_fn backup_top_co_pdiscard(BlockDriverState *bs,
+ int64_t offset, int bytes)
+{
+ int ret = backup_top_cbw(bs, offset, bytes);
+ if (ret < 0) {
+ return ret;
+ }
+
+ return bdrv_co_pdiscard(bs->backing, offset, bytes);
+}
+
+static int coroutine_fn backup_top_co_pwrite_zeroes(BlockDriverState *bs,
+ int64_t offset, int bytes, BdrvRequestFlags flags)
+{
+ int ret = backup_top_cbw(bs, offset, bytes);
+ if (ret < 0) {
+ return ret;
+ }
+
+ return bdrv_co_pwrite_zeroes(bs->backing, offset, bytes, flags);
+}
+
+static coroutine_fn int backup_top_co_pwritev(BlockDriverState *bs,
+ uint64_t offset,
+ uint64_t bytes,
+ QEMUIOVector *qiov, int flags)
+{
+ if (!(flags & BDRV_REQ_WRITE_UNCHANGED)) {
+ int ret = backup_top_cbw(bs, offset, bytes);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+
+ return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
+}
+
+static int coroutine_fn backup_top_co_flush(BlockDriverState *bs)
+{
+ if (!bs->backing) {
+ return 0;
+ }
+
+ return bdrv_co_flush(bs->backing->bs);
+}
+
+static void backup_top_refresh_filename(BlockDriverState *bs)
+{
+ if (bs->backing == NULL) {
+ /*
+ * we can be here after failed bdrv_attach_child in
+ * bdrv_set_backing_hd
+ */
+ return;
+ }
+ pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
+ bs->backing->bs->filename);
+}
+
+static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
+ const BdrvChildRole *role,
+ BlockReopenQueue *reopen_queue,
+ uint64_t perm, uint64_t shared,
+ uint64_t *nperm, uint64_t *nshared)
+{
+ BDRVBackupTopState *s = bs->opaque;
+
+ if (!s->active) {
+ /*
+ * The filter node may be in process of bdrv_append(), which firstly do
+ * bdrv_set_backing_hd() and then bdrv_replace_node(). This means that
+ * we can't unshare BLK_PERM_WRITE during bdrv_append() operation. So,
+ * let's require nothing during bdrv_append() and refresh permissions
+ * after it (see bdrv_backup_top_append()).
+ */
+ *nperm = 0;
+ *nshared = BLK_PERM_ALL;
+ return;
+ }
+
+ if (role == &child_file) {
+ /*
+ * Target child
+ *
+ * Share write to target (child_file), to not interfere
+ * with guest writes to its disk which may be in target backing chain.
+ */
+ *nshared = BLK_PERM_ALL;
+ *nperm = BLK_PERM_WRITE;
+ } else {
+ /* Source child */
+ bdrv_filter_default_perms(bs, c, role, reopen_queue, perm, shared,
+ nperm, nshared);
+
+ if (perm & BLK_PERM_WRITE) {
+ *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
+ }
+ *nshared &= ~BLK_PERM_WRITE;
+ }
+}
+
+BlockDriver bdrv_backup_top_filter = {
+ .format_name = "backup-top",
+ .instance_size = sizeof(BDRVBackupTopState),
+
+ .bdrv_co_preadv = backup_top_co_preadv,
+ .bdrv_co_pwritev = backup_top_co_pwritev,
+ .bdrv_co_pwrite_zeroes = backup_top_co_pwrite_zeroes,
+ .bdrv_co_pdiscard = backup_top_co_pdiscard,
+ .bdrv_co_flush = backup_top_co_flush,
+
+ .bdrv_co_block_status = bdrv_co_block_status_from_backing,
+
+ .bdrv_refresh_filename = backup_top_refresh_filename,
+
+ .bdrv_child_perm = backup_top_child_perm,
+
+ .is_filter = true,
+};
+
+BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
+ BlockDriverState *target,
+ const char *filter_node_name,
+ uint64_t cluster_size,
+ BdrvRequestFlags write_flags,
+ BlockCopyState **bcs,
+ Error **errp)
+{
+ Error *local_err = NULL;
+ BDRVBackupTopState *state;
+ BlockDriverState *top = bdrv_new_open_driver(&bdrv_backup_top_filter,
+ filter_node_name,
+ BDRV_O_RDWR, errp);
+
+ if (!top) {
+ return NULL;
+ }
+
+ top->total_sectors = source->total_sectors;
+ top->opaque = state = g_new0(BDRVBackupTopState, 1);
+
+ bdrv_ref(target);
+ state->target = bdrv_attach_child(top, target, "target", &child_file, errp);
+ if (!state->target) {
+ bdrv_unref(target);
+ bdrv_unref(top);
+ return NULL;
+ }
+
+ bdrv_drained_begin(source);
+
+ bdrv_ref(top);
+ bdrv_append(top, source, &local_err);
+ if (local_err) {
+ error_prepend(&local_err, "Cannot append backup-top filter: ");
+ goto append_failed;
+ }
+
+ /*
+ * bdrv_append() finished successfully, now we can require permissions
+ * we want.
+ */
+ state->active = true;
+ bdrv_child_refresh_perms(top, top->backing, &local_err);
+ if (local_err) {
+ error_prepend(&local_err,
+ "Cannot set permissions for backup-top filter: ");
+ goto failed_after_append;
+ }
+
+ /*
+ * TODO: Create block-copy-state here (which will utilize @cluster_size and
+ * @write_flags parameters which are unused now). For this, block-copy
+ * should be refactored to use BdrvChildren.
+ */
+ state->bcs = NULL;
+ if (!state->bcs) {
+ error_setg(&local_err, "Cannot create block-copy-state");
+ goto failed_after_append;
+ }
+ *bcs = state->bcs;
+
+ bdrv_drained_end(source);
+
+ return top;
+
+failed_after_append:
+ state->active = false;
+ bdrv_backup_top_drop(top);
+
+append_failed:
+ bdrv_drained_end(source);
+ bdrv_unref_child(top, state->target);
+ bdrv_unref(top);
+ error_propagate(errp, local_err);
+
+ return NULL;
+}
+
+void bdrv_backup_top_drop(BlockDriverState *bs)
+{
+ BDRVBackupTopState *s = bs->opaque;
+ AioContext *aio_context = bdrv_get_aio_context(bs);
+
+ block_copy_state_free(s->bcs);
+
+ aio_context_acquire(aio_context);
+
+ bdrv_drained_begin(bs);
+
+ s->active = false;
+ bdrv_child_refresh_perms(bs, bs->backing, &error_abort);
+ bdrv_replace_node(bs, backing_bs(bs), &error_abort);
+ bdrv_set_backing_hd(bs, NULL, &error_abort);
+
+ bdrv_drained_end(bs);
+
+ bdrv_unref(bs);
+
+ aio_context_release(aio_context);
+}
@@ -42,6 +42,7 @@ block-obj-y += block-copy.o
block-obj-y += crypto.o
block-obj-y += aio_task.o
+block-obj-y += backup-top.o
common-obj-y += stream.o
Backup-top filter caches write operations and does copy-before-write operations. The driver will be used in backup instead of write-notifiers. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> --- block/backup-top.h | 41 +++++++ block/backup-top.c | 281 ++++++++++++++++++++++++++++++++++++++++++++ block/Makefile.objs | 1 + 3 files changed, 323 insertions(+) create mode 100644 block/backup-top.h create mode 100644 block/backup-top.c