[Qemu-block] [PATCH v3 1/1] block: pass the right options for BlockDriver.bdrv_open()

[Dong Jia Shi]

raw_open() expects the caller always passing in the right actual
@options parameter. But when trying to applying snapshot on a RBD
image, bdrv_snapshot_goto() calls raw_open() (by calling the
bdrv_open callback on the BlockDriver) with a NULL @options, and
that will result in a Segmentation fault.

For the other non-raw format drivers, it also makes sense to passing
in the actual options, althought they don't trigger the problem so
far.

Let's prepare a @options by adding the "file" key-value pair to a
copy of the actual options that were given for the node (i.e.
bs->options), and pass it to the callback.

BlockDriver.bdrv_open() expects bs->file to be NULL and just
overwrites it with the result from bdrv_open_child(). If that
bdrv_open_child() fails, the field becomes NULL. While we are at
it, we also correct the cleanning up action for a call failure of
BlockDriver.bdrv_open() by replacing bdrv_unref() with
bdrv_unref_child().

Suggested-by: Max Reitz <address@hidden>
Signed-off-by: Dong Jia Shi <address@hidden>
---
 block/snapshot.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index bf5c2ca..281626c 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -27,6 +27,7 @@
 #include "block/block_int.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qstring.h"
 
 QemuOptsList internal_snapshot_opts = {
     .name = "snapshot",
@@ -189,11 +190,20 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
     }
 
     if (bs->file) {
+        QDict *options = qdict_clone_shallow(bs->options);
+        QDict *file_options;
+
+        qdict_extract_subqdict(options, &file_options, "file.");
+        QDECREF(file_options);
+        qdict_put(options, "file",
+                  qstring_from_str(bdrv_get_node_name(bs->file->bs)));
+
         drv->bdrv_close(bs);
         ret = bdrv_snapshot_goto(bs->file->bs, snapshot_id);
-        open_ret = drv->bdrv_open(bs, NULL, bs->open_flags, NULL);
+        open_ret = drv->bdrv_open(bs, options, bs->open_flags, NULL);
+        QDECREF(options);
         if (open_ret < 0) {
-            bdrv_unref(bs->file->bs);
+            bdrv_unref_child(bs, bs->file);
             bs->drv = NULL;
             return open_ret;
         }
-- 
2.8.4