Re: [PATCH v15 4/5] block: introduce backup-top filter driver

[Max Reitz]

On 01.10.19 15:14, Vladimir Sementsov-Ogievskiy wrote:
> 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 
> ---
>  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

Reviewed-by: Max Reitz 



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[PATCH v15 4/5] block: introduce backup-top filter driver

[Vladimir Sementsov-Ogievskiy]

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 
---
 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

diff --git a/block/backup-top.h b/block/backup-top.h
new file mode 100644
index 00..e5cabfa197
--- /dev/null
+++ b/block/backup-top.h
@@ -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 
+ *
+ * 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 .
+ */
+
+#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 */
diff --git a/block/backup-top.c b/block/backup-top.c
new file mode 100644
index 00..75a315744d
--- /dev/null
+++ b/block/backup-top.c
@@ -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 
+ *
+ * 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 .
+ */
+
+#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,
+