[Qemu-devel] [PATCH 08/21] backup: skip unallocated clusters for full mode

[Vladimir Sementsov-Ogievskiy]

In case of full backup we can skip unallocated clusters if the target
disk is already zero-initialized.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
 block/backup.c         | 8 ++++++--
 tests/qemu-iotests/055 | 2 ++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index 2afd1b6..4ef8daf 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -562,9 +562,13 @@ static void coroutine_fn backup_run(void *opaque)
         if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
             backup_incremental_init_copy_bitmap(job);
         } else {
+            /* top or full mode */
+            bool is_top = job->sync_mode == MIRROR_SYNC_MODE_TOP;
+            BlockDriverState *base =
+                    is_top ? backing_bs(blk_bs(job->common.blk)) : NULL;
             hbitmap_set(job->copy_bitmap, 0, end);
-            if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
-                backup_skip_loop(job, backing_bs(blk_bs(job->common.blk)));
+            if (is_top || bdrv_has_zero_init(blk_bs(job->target))) {
+                backup_skip_loop(job, base);
             }
         }
         ret = backup_loop(job);
diff --git a/tests/qemu-iotests/055 b/tests/qemu-iotests/055
index 1d3fd04..388b7b2 100755
--- a/tests/qemu-iotests/055
+++ b/tests/qemu-iotests/055
@@ -30,6 +30,7 @@ target_img = os.path.join(iotests.test_dir, 'target.img')
 blockdev_target_img = os.path.join(iotests.test_dir, 'blockdev-target.img')
 
 image_len = 64 * 1024 * 1024 # MB
+pause_write = '3M'
 
 def setUpModule():
     qemu_img('create', '-f', iotests.imgfmt, test_img, str(image_len))
@@ -39,6 +40,7 @@ def setUpModule():
     qemu_io('-f', iotests.imgfmt, '-c', 'write -P0xd5 1M 32k', test_img)
     qemu_io('-f', iotests.imgfmt, '-c', 'write -P0xdc 32M 124k', test_img)
     qemu_io('-f', iotests.imgfmt, '-c', 'write -P0x33 67043328 64k', test_img)
+    qemu_io('-f', iotests.imgfmt, '-c', 'write -P0xdc 40M ' + pause_write, 
test_img)
 
 def tearDownModule():
     os.remove(test_img)
-- 
1.8.3.1