[Qemu-devel] [PATCH V4 03/13] block: add bdrv_can_read_snapshot() function

[Wenchao Xia]

  Compared to bdrv_can_snapshot(), this function return whether
bs* is ready to read snapshot info from instead of write. If yes,
caller can then query snapshot information, but taking snapshot
is not always possible for that *bs may be read only.

Signed-off-by: Wenchao Xia <address@hidden>
---
 block.c               |   19 +++++++++++++++++++
 include/block/block.h |    1 +
 2 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index a86257d..934bb3f 100644
--- a/block.c
+++ b/block.c
@@ -3091,6 +3091,25 @@ bool bdrv_debug_is_suspended(BlockDriverState *bs, const 
char *tag)
 /**************************************************************/
 /* handling of snapshots */
 
+/* return whether internal snapshot can be read on @bs */
+int bdrv_can_read_snapshot(BlockDriverState *bs)
+{
+    BlockDriver *drv = bs->drv;
+    if (!drv || !bdrv_is_inserted(bs)) {
+        return 0;
+    }
+
+    if (!drv->bdrv_snapshot_create) {
+        if (bs->file != NULL) {
+            return bdrv_can_read_snapshot(bs->file);
+        }
+        return 0;
+    }
+
+    return 1;
+}
+
+/* return whether internal snapshot can be write on @bs */
 int bdrv_can_snapshot(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
diff --git a/include/block/block.h b/include/block/block.h
index 0b84e9b..b4c1612 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -318,6 +318,7 @@ void bdrv_get_full_backing_filename(BlockDriverState *bs,
                                     char *dest, size_t sz);
 BlockInfo *bdrv_query_info(BlockDriverState *s);
 BlockStats *bdrv_query_stats(const BlockDriverState *bs);
+int bdrv_can_read_snapshot(BlockDriverState *bs);
 int bdrv_can_snapshot(BlockDriverState *bs);
 int bdrv_is_snapshot(BlockDriverState *bs);
 BlockDriverState *bdrv_snapshots(void);
-- 
1.7.1