[Qemu-devel] [PATCH 7/9] block: add differential backup mode

[John Snow <jsnow@redhat.com>]

This is simple: instead of clearing the bitmap, just leave the bitmap
data intact even in case of success.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 block.c               |  9 ++++++++-
 block/backup.c        | 17 ++++++++++-------
 block/mirror.c        |  9 +++++++--
 include/block/block.h |  1 +
 qapi/block-core.json  |  6 ++++--
 5 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/block.c b/block.c
index 5551f79..3e780f9 100644
--- a/block.c
+++ b/block.c
@@ -3166,7 +3166,9 @@ DirtyBitmapStatus bdrv_dirty_bitmap_status(BdrvDirtyBitmap *bitmap)
  * Requires that the bitmap is not frozen and has no successor.
  */
 int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
-                                       BdrvDirtyBitmap *bitmap, Error **errp)
+                                       BdrvDirtyBitmap *bitmap,
+                                       MirrorSyncMode sync_mode,
+                                       Error **errp)
 {
     uint64_t granularity;
     BdrvDirtyBitmap *child;
@@ -3191,6 +3193,11 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
     /* Install the successor and freeze the parent */
     bitmap->successor = child;
     bitmap->successor_refcount = 1;
+
+    if (sync_mode == MIRROR_SYNC_MODE_DIFFERENTIAL) {
+        bitmap->act = SUCCESSOR_ACTION_RECLAIM;
+    }
+
     return 0;
 }
 
diff --git a/block/backup.c b/block/backup.c
index a8f7c43..dd808c2 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -390,7 +390,8 @@ static void coroutine_fn backup_run(void *opaque)
             qemu_coroutine_yield();
             job->common.busy = true;
         }
-    } else if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
+    } else if ((job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) ||
+               (job->sync_mode == MIRROR_SYNC_MODE_DIFFERENTIAL)) {
         ret = backup_run_incremental(job);
     } else {
         /* Both FULL and TOP SYNC_MODE's require copying.. */
@@ -510,15 +511,18 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
         return;
     }
 
-    if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
+    if ((sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) ||
+        (sync_mode == MIRROR_SYNC_MODE_DIFFERENTIAL)) {
         if (!sync_bitmap) {
-            error_setg(errp, "must provide a valid bitmap name for "
-                             "\"incremental\" sync mode");
+            error_setg(errp,
+                       "must provide a valid bitmap name for \"%s\" sync mode",
+                       MirrorSyncMode_lookup[sync_mode]);
             return;
         }
 
         /* Create a new bitmap, and freeze/disable this one. */
-        if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
+        if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap,
+                                               sync_mode, errp) < 0) {
             return;
         }
     } else if (sync_bitmap) {
@@ -548,8 +552,7 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
     job->on_target_error = on_target_error;
     job->target = target;
     job->sync_mode = sync_mode;
-    job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
-                       sync_bitmap : NULL;
+    job->sync_bitmap = sync_bitmap;
     job->common.len = len;
     job->common.co = qemu_coroutine_create(backup_run);
     qemu_coroutine_enter(job->common.co, job);
diff --git a/block/mirror.c b/block/mirror.c
index adf391c..1cde86b 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -709,9 +709,14 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
     bool is_none_mode;
     BlockDriverState *base;
 
-    if (mode == MIRROR_SYNC_MODE_INCREMENTAL) {
-        error_setg(errp, "Sync mode 'incremental' not supported");
+    switch (mode) {
+    case MIRROR_SYNC_MODE_INCREMENTAL:
+    case MIRROR_SYNC_MODE_DIFFERENTIAL:
+        error_setg(errp, "Sync mode \"%s\" not supported",
+                   MirrorSyncMode_lookup[mode]);
         return;
+    default:
+        break;
     }
     is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
     base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
diff --git a/include/block/block.h b/include/block/block.h
index e88a332..8169a60 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -462,6 +462,7 @@ BdrvDirtyBitmap *bdrv_copy_dirty_bitmap(BlockDriverState *bs,
                                         Error **errp);
 int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
                                        BdrvDirtyBitmap *bitmap,
+                                       MirrorSyncMode sync_mode,
                                        Error **errp);
 BdrvDirtyBitmap *bdrv_frozen_bitmap_decref(BlockDriverState *bs,
                                            BdrvDirtyBitmap *parent,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 92c9e53..421fd25 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -534,12 +534,14 @@
 #
 # @none: only copy data written from now on
 #
-# @incremental: only copy data described by the dirty bitmap. Since: 2.4
+# @incremental: Copy data described by the bitmap, and clear it. Since: 2.4
+#
+# @differential: Copy data described by the bitmap, don't clear it. Since: 2.4
 #
 # Since: 1.3
 ##
 { 'enum': 'MirrorSyncMode',
-  'data': ['top', 'full', 'none', 'incremental'] }
+  'data': ['top', 'full', 'none', 'incremental', 'differential'] }
 
 ##
 # @BlockJobType:
-- 
2.1.0