block: introduce bdrv_swap, implement bdrv_append on top of it

The new function can be made a bit nicer than bdrv_append.  It swaps the
whole contents, and then swaps back (using the usual t=a;a=b;b=t idiom)
the fields that need to stay on top.  Thus, it does not need explicit
bdrv_detach_dev, bdrv_iostatus_disable, etc.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block.h b/block.h
index 42e30d6a7c..3af93c6266 100644
--- a/block.h
+++ b/block.h
@@ -122,6 +122,7 @@ int bdrv_create(BlockDriver *drv, const char* filename,
 int bdrv_create_file(const char* filename, QEMUOptionParameter *options);
 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_delete(BlockDriverState *bs);
 int bdrv_parse_cache_flags(const char *mode, int *flags);