[Qemu-devel] [PATCH v4 2/7] qmp: add internal sync mode "common" to mirror_start

[Fam Zheng <famz@redhat.com>]

This adds a new sync mode "common" which only copies data that is above
the common ancestor of source and target. In general, this could be useful
in cases like:

    base_bs ---> common_ancestor ---> foo ---> bar --->source
                                  \
                                   \---> target

Where data in foo, bar and source will be copied to target, once such
common backing_hd sharing is introduced. For now, we could use a special
case: If target is the ancestor of source, like,

    base_bs ---> target ---> foo ---> bar --->source

The data in foo, bar and source will be copied to target, like
drive-commit, and when they are synced, the source bs replaces target
bs. This is specifically useful for block commit of active layer.

This mode is not available (-ENOTSUP) from QMP interface, it is only
used internally by block commit code.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/mirror.c             | 16 ++++++++++++++--
 blockdev.c                 |  5 +++++
 qapi-schema.json           |  2 +-
 tests/qemu-iotests/041     |  5 +++++
 tests/qemu-iotests/041.out |  4 ++--
 5 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 6e7a274..fdc7fa8 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -31,6 +31,7 @@ typedef struct MirrorBlockJob {
     BlockJob common;
     RateLimit limit;
     BlockDriverState *target;
+    BlockDriverState *base;
     MirrorSyncMode mode;
     BlockdevOnError on_source_error, on_target_error;
     bool synced;
@@ -334,8 +335,7 @@ static void coroutine_fn mirror_run(void *opaque)
 
     if (s->mode != MIRROR_SYNC_MODE_NONE) {
         /* First part, loop on the sectors and initialize the dirty bitmap.  */
-        BlockDriverState *base;
-        base = s->mode == MIRROR_SYNC_MODE_FULL ? NULL : bs->backing_hd;
+        BlockDriverState *base = s->base;
         for (sector_num = 0; sector_num < end; ) {
             int64_t next = (sector_num | (sectors_per_chunk - 1)) + 1;
             ret = bdrv_is_allocated_above(bs, base,
@@ -541,6 +541,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
                   void *opaque, Error **errp)
 {
     MirrorBlockJob *s;
+    BlockDriverState *base = NULL;
 
     if (granularity == 0) {
         /* Choose the default granularity based on the target file's cluster
@@ -563,6 +564,16 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
         return;
     }
 
+    if (mode == MIRROR_SYNC_MODE_COMMON) {
+        base = bdrv_common_ancestor(bs, target);
+        if (!base) {
+            error_setg(errp, "source and target has no common ancestor");
+            return;
+        }
+    } else if (mode == MIRROR_SYNC_MODE_TOP) {
+        base = bs->backing_hd;
+    }
+
     s = block_job_create(&mirror_job_type, bs, speed, cb, opaque, errp);
     if (!s) {
         return;
@@ -572,6 +583,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
     s->on_target_error = on_target_error;
     s->target = target;
     s->mode = mode;
+    s->base = base;
     s->granularity = granularity;
     s->buf_size = MAX(buf_size, granularity);
 
diff --git a/blockdev.c b/blockdev.c
index 8aa66a9..3acd330 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1906,6 +1906,11 @@ void qmp_drive_mirror(const char *device, const char *target,
         return;
     }
 
+    if (sync == MIRROR_SYNC_MODE_COMMON) {
+        error_set(errp, QERR_UNSUPPORTED);
+        return;
+    }
+
     flags = bs->open_flags | BDRV_O_RDWR;
     source = bs->backing_hd;
     if (!source && sync == MIRROR_SYNC_MODE_TOP) {
diff --git a/qapi-schema.json b/qapi-schema.json
index 145eca8..6addf49 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1363,7 +1363,7 @@
 # Since: 1.3
 ##
 { 'enum': 'MirrorSyncMode',
-  'data': ['top', 'full', 'none'] }
+  'data': ['top', 'full', 'none', 'common'] }
 
 ##
 # @BlockJobInfo:
diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index 6661c03..86b3251 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -206,6 +206,11 @@ class TestSingleDrive(ImageMirroringTestCase):
                              target=target_img)
         self.assert_qmp(result, 'error/class', 'DeviceNotFound')
 
+    def test_common(self):
+        result = self.vm.qmp('drive-mirror', device='drive0', sync='common',
+                             target=target_img)
+        self.assert_qmp(result, 'error/class', 'GenericError')
+
 class TestMirrorNoBacking(ImageMirroringTestCase):
     image_len = 2 * 1024 * 1024 # MB
 
diff --git a/tests/qemu-iotests/041.out b/tests/qemu-iotests/041.out
index 42314e9..4fd1c2d 100644
--- a/tests/qemu-iotests/041.out
+++ b/tests/qemu-iotests/041.out
@@ -1,5 +1,5 @@
-........................
+.........................
 ----------------------------------------------------------------------
-Ran 24 tests
+Ran 25 tests
 
 OK
-- 
1.8.3.1