[Qemu-devel] [PATCH v10 11/13] qapi: Add transaction support to block-dirty-bitmap-{add, enable, disable}

[John Snow <jsnow@redhat.com>]

From: Fam Zheng <famz@redhat.com>

This adds three qmp commands to transactions.

Users can stop a dirty bitmap, start backup of it, and start another
dirty bitmap atomically, so that the dirty bitmap is tracked
incrementally and we don't miss any write.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 blockdev.c       | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qapi-schema.json |   5 ++-
 2 files changed, 104 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 0b38571..209fedd 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1602,6 +1602,89 @@ static void drive_backup_clean(BlkTransactionState *common)
     }
 }
 
+static void block_dirty_bitmap_add_prepare(BlkTransactionState *common,
+                                           Error **errp)
+{
+    BlockDirtyBitmapAdd *action;
+
+    action = common->action->block_dirty_bitmap_add;
+    qmp_block_dirty_bitmap_add(action->node_ref, action->name,
+                               action->has_granularity, action->granularity,
+                               errp);
+}
+
+static void block_dirty_bitmap_add_abort(BlkTransactionState *common)
+{
+    BlockDirtyBitmapAdd *action;
+
+    action = common->action->block_dirty_bitmap_add;
+    /* Should not fail meaningfully: IF the bitmap was added via .prepare(),
+     * then the node reference and bitmap name must have been valid.
+     * THUS: any failure here could only indicate the lack of a bitmap at all.
+     */
+    qmp_block_dirty_bitmap_remove(action->node_ref, action->name, NULL);
+}
+
+typedef struct BlockDirtyBitmapState {
+    BlkTransactionState common;
+    BdrvDirtyBitmap *bitmap;
+    AioContext *aio_context;
+} BlockDirtyBitmapState;
+
+/**
+ * Enable and Disable re-use the same preparation.
+ */
+static void block_dirty_bitmap_toggle_prepare(BlkTransactionState *common,
+                                              Error **errp)
+{
+    BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
+                                             common, common);
+    BlockDirtyBitmap *action;
+    BlockDriverState *bs;
+
+    /* We may be used by either enable or disable;
+     * We use the "enable" member of the union here,
+     * but "disable" should be functionally equivalent: */
+    action = common->action->block_dirty_bitmap_enable;
+    assert(action == common->action->block_dirty_bitmap_disable);
+
+    state->bitmap = block_dirty_bitmap_lookup(action->node_ref,
+                                              action->name,
+                                              &bs,
+                                              errp);
+    if (!state->bitmap) {
+        return;
+    }
+
+    /* AioContext is released in .clean() */
+    state->aio_context = bdrv_get_aio_context(bs);
+    aio_context_acquire(state->aio_context);
+}
+
+static void block_dirty_bitmap_enable_commit(BlkTransactionState *common)
+{
+    BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
+                                             common, common);
+    bdrv_enable_dirty_bitmap(state->bitmap);
+}
+
+static void block_dirty_bitmap_disable_commit(BlkTransactionState *common)
+{
+    BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
+                                             common, common);
+    bdrv_disable_dirty_bitmap(state->bitmap);
+}
+
+static void block_dirty_bitmap_toggle_clean(BlkTransactionState *common)
+{
+    BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
+                                             common, common);
+
+    if (state->aio_context) {
+        aio_context_release(state->aio_context);
+    }
+}
+
 static void abort_prepare(BlkTransactionState *common, Error **errp)
 {
     error_setg(errp, "Transaction aborted using Abort action");
@@ -1636,6 +1719,23 @@ static const BdrvActionOps actions[] = {
         .abort = internal_snapshot_abort,
         .clean = internal_snapshot_clean,
     },
+    [TRANSACTION_ACTION_KIND_BLOCK_DIRTY_BITMAP_ADD] = {
+        .instance_size = sizeof(BlkTransactionState),
+        .prepare = block_dirty_bitmap_add_prepare,
+        .abort = block_dirty_bitmap_add_abort,
+    },
+    [TRANSACTION_ACTION_KIND_BLOCK_DIRTY_BITMAP_ENABLE] = {
+        .instance_size = sizeof(BlockDirtyBitmapState),
+        .prepare = block_dirty_bitmap_toggle_prepare,
+        .commit = block_dirty_bitmap_enable_commit,
+        .clean = block_dirty_bitmap_toggle_clean,
+    },
+    [TRANSACTION_ACTION_KIND_BLOCK_DIRTY_BITMAP_DISABLE] = {
+        .instance_size = sizeof(BlockDirtyBitmapState),
+        .prepare = block_dirty_bitmap_toggle_prepare,
+        .commit = block_dirty_bitmap_disable_commit,
+        .clean = block_dirty_bitmap_toggle_clean,
+    },
 };
 
 /*
diff --git a/qapi-schema.json b/qapi-schema.json
index 563b4ad..85f55d9 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1260,7 +1260,10 @@
        'blockdev-snapshot-sync': 'BlockdevSnapshot',
        'drive-backup': 'DriveBackup',
        'abort': 'Abort',
-       'blockdev-snapshot-internal-sync': 'BlockdevSnapshotInternal'
+       'blockdev-snapshot-internal-sync': 'BlockdevSnapshotInternal',
+       'block-dirty-bitmap-add': 'BlockDirtyBitmapAdd',
+       'block-dirty-bitmap-enable': 'BlockDirtyBitmap',
+       'block-dirty-bitmap-disable': 'BlockDirtyBitmap'
    } }
 
 ##
-- 
1.9.3