[Qemu-stable] [PATCH] block: Use BDRV_O_NO_BACKING where appropriate

[Benoît Canet]

From: Kevin Wolf <address@hidden>

If you open an image temporarily just because you want to check its size
or get it flushed, there's no real reason to open the whole backing file
chain.

This is a backport of c9fbb99d41b05acf0d7b93deb2fcdbf9047c238e to
qemu 1.7.1.

The backport was done to fix a bug where QEMU 1.7.1 would crash or freeze
when the user take around 80 consecutives snapshots in a row.

git bisect would lead to commit: ba2ab2f2ca4150a7e314fbb19fa158bd8ddc36eb
and it was clear that BDRV_NO_BACKING was missing.

Signed-off-by: Kevin Wolf <address@hidden>
Signed-off-by: Benoit Canet <address@hidden>
---
 block.c       |    4 ++--
 block/qcow2.c |    3 ++-
 block/vmdk.c  |    2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/block.c b/block.c
index 382ea71..9f638ea 100644
--- a/block.c
+++ b/block.c
@@ -1064,9 +1064,9 @@ int bdrv_open(BlockDriverState *bs, const char *filename, 
QDict *options,
         /* if snapshot, we create a temporary backing file and open it
            instead of opening 'filename' directly */
 
-        /* if there is a backing file, use it */
         bs1 = bdrv_new("");
-        ret = bdrv_open(bs1, filename, NULL, 0, drv, &local_err);
+        ret = bdrv_open(bs1, filename, NULL, BDRV_O_NO_BACKING, drv,
+                        &local_err);
         if (ret < 0) {
             bdrv_unref(bs1);
             goto fail;
diff --git a/block/qcow2.c b/block/qcow2.c
index 6e5d98d..344c63e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1588,7 +1588,8 @@ static int qcow2_create2(const char *filename, int64_t 
total_size,
 
     /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning */
     ret = bdrv_open(bs, filename, NULL,
-                    BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);
+                    BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_BACKING,
+                    drv, &local_err);
     if (error_is_set(&local_err)) {
         error_propagate(errp, local_err);
         goto out;
diff --git a/block/vmdk.c b/block/vmdk.c
index a7ebd0f..d35a9d7 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1689,7 +1689,7 @@ static int vmdk_create(const char *filename, 
QEMUOptionParameter *options,
     }
     if (backing_file) {
         BlockDriverState *bs = bdrv_new("");
-        ret = bdrv_open(bs, backing_file, NULL, 0, NULL, errp);
+        ret = bdrv_open(bs, backing_file, NULL, BDRV_O_NO_BACKING, NULL, errp);
         if (ret != 0) {
             bdrv_unref(bs);
             return ret;
-- 
1.7.10.4