[Qemu-devel] [PATCH 12/14] block: pass BDRV_BACKING flag to open of a backing file

[Uri Lublin <uril@redhat.com>]

There may exist some actions needed to be taken only by
the leaf image (and not backing images), such as keeping track
of highest-allocation-offset.

Signed-off-by: Uri Lublin <uril@redhat.com>
---
 block.c |    3 ++-
 block.h |    2 ++
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/block.c b/block.c
index 39ff1dd..8d92d9e 100644
--- a/block.c
+++ b/block.c
@@ -415,7 +415,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
     /* Note: for compatibility, we open disk image files as RDWR, and
        RDONLY as fallback */
     if (!(flags & BDRV_O_FILE))
-        open_flags = BDRV_O_RDWR | (flags & BDRV_O_CACHE_MASK);
+        open_flags = BDRV_O_RDWR | (flags & (BDRV_O_CACHE_MASK | BDRV_O_BACKING));
     else
         open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
     ret = drv->bdrv_open(bs, filename, open_flags);
@@ -446,6 +446,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
         bs->backing_hd = bdrv_new("");
         path_combine(backing_filename, sizeof(backing_filename),
                      filename, bs->backing_file);
+        open_flags |= BDRV_O_BACKING;
         if (bs->backing_format[0] != '\0')
             back_drv = bdrv_find_format(bs->backing_format);
         ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
diff --git a/block.h b/block.h
index fbb445e..18147cf 100644
--- a/block.h
+++ b/block.h
@@ -56,6 +56,8 @@ typedef struct QEMUSnapshotInfo {
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_CACHE_DEF)
 
+#define BDRV_O_BACKING     0x0100 /* a backing file */
+
 void bdrv_info(Monitor *mon);
 void bdrv_info_stats(Monitor *mon);
 
-- 
1.6.0.6