[Qemu-devel] [PATCH v4 1/7] block: add bdrv_common_ancestor()

[Fam Zheng <famz@redhat.com>]

This function finds the common ancestor in backing chain of two BDSes.
If there's no common ancestor, NULL is returned.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c               | 15 +++++++++++++++
 include/block/block.h |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/block.c b/block.c
index ea4956d..db1381d 100644
--- a/block.c
+++ b/block.c
@@ -3036,6 +3036,21 @@ BlockDriverState *bdrv_find(const char *name)
     return NULL;
 }
 
+BlockDriverState *bdrv_common_ancestor(BlockDriverState *bs1,
+                                       BlockDriverState *bs2)
+{
+    /* TODO: higher efficiency with reverse linked backing chain */
+    BlockDriverState *base1, *base2;
+    for (base1 = bs1; base1; base1 = base1->backing_hd) {
+        for (base2 = bs2; base2; base2 = base2->backing_hd) {
+            if (base1 == base2) {
+                return base1;
+            }
+        }
+    }
+    return NULL;
+}
+
 BlockDriverState *bdrv_next(BlockDriverState *bs)
 {
     if (!bs) {
diff --git a/include/block/block.h b/include/block/block.h
index f808550..e095f16 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -321,6 +321,8 @@ void bdrv_lock_medium(BlockDriverState *bs, bool locked);
 void bdrv_eject(BlockDriverState *bs, bool eject_flag);
 const char *bdrv_get_format_name(BlockDriverState *bs);
 BlockDriverState *bdrv_find(const char *name);
+BlockDriverState *bdrv_common_ancestor(BlockDriverState *bs1,
+                                       BlockDriverState *bs2);
 BlockDriverState *bdrv_next(BlockDriverState *bs);
 void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs),
                   void *opaque);
-- 
1.8.3.1