block: Use BDRV_O_NO_BACKING where appropriate

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 <kwolf@redhat.com>
Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/block.c b/block.c
index 8f84dbc5cb3ad4196f7312c77caec8cd0b13d82c..68651a9ba442736c185569b8f5e815ae9b7dc4bb 100644 (file)
--- a/block.c
+++ b/block.c
@@ -1067,9 +1067,9 @@ 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 b43c7d0a3e228ebe9b3738edf34c6631a5fb701e..f2897b64aa4ee0e077e705ad287fc5eb536b890a 100644 (file)
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1605,7 +1605,8 @@ 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 a7ebd0f1257c76dfe64d61cc7228209b0a94b12a..d35a9d7e02317205949c4a04b8927962806de0e4 100644 (file)
--- 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;