[Qemu-devel] [PATCH V2 02/10] block: add function deappend()

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

  This function should revert the append operation.

Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
---
 block.c               |   21 +++++++++++++++++++++
 include/block/block.h |    1 +
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index 09208c2..48ddf64 100644
--- a/block.c
+++ b/block.c
@@ -1376,6 +1376,27 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top)
             bs_new->drv ? bs_new->drv->format_name : "");
 }
 
+/*
+ * Remove bs contents which is at the top of an image chain while
+ * the chain is live. After bdrv_append(bs_new, bs_top) called,
+ * bs_top keeps as the top of the chain but bs_new become the 2nd
+ * top one, so call bdrv_deappend(bs_new, bs_top) to cancel the change.
+ * As a result, bs_top still keeps the top position but bs_new is
+ * is discarded.
+ *
+ * This will modify the BlockDriverState fields, and swap contents
+ * between bs_old and bs_top. Both bs_old and bs_top are modified.
+ *
+ * bs_old and bs_top should be the pairs which have been used in
+ * bdrv_append().
+ *
+ * This function does not delete any image files.
+ */
+void bdrv_deappend(BlockDriverState *bs_old, BlockDriverState *bs_top)
+{
+    bdrv_swap(bs_old, bs_top);
+}
+
 void bdrv_delete(BlockDriverState *bs)
 {
     assert(!bs->dev);
diff --git a/include/block/block.h b/include/block/block.h
index a49fd71..ae6a5ae 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -130,6 +130,7 @@ BlockDriverState *bdrv_new(const char *device_name);
 void bdrv_make_anon(BlockDriverState *bs);
 void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old);
 void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
+void bdrv_deappend(BlockDriverState *bs_old, BlockDriverState *bs_top);
 void bdrv_delete(BlockDriverState *bs);
 int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
-- 
1.7.1