block: Bugfix 'format' and 'snapshot' used in drive option

When use -drive file='xxx',format=qcow2,snapshot=on the error
message "Can't use snapshot=on with driver-specific options"
can be show, and fail to start the qemu.

This should not be happened, and there is no file.driver option
in qemu command line.

It is because the commit 74fe54f2,
it puts 'driver' option if the command line use 'format' option.

This patch is to solve this bug.
Signed-off-by: NMike Qiu <qiudayu@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -340,6 +340,7 @@ static DriveInfo *blockdev_init(QemuOpts *all_opts,
     QDict *bs_opts;
     const char *id;
     bool has_driver_specific_opts;
+    BlockDriver *drv = NULL;
 
     translation = BIOS_ATA_TRANSLATION_AUTO;
     media = MEDIA_DISK;
@@ -485,7 +486,11 @@ static DriveInfo *blockdev_init(QemuOpts *all_opts,
             return NULL;
         }
 
-        qdict_put(bs_opts, "driver", qstring_from_str(buf));
+        drv = bdrv_find_whitelisted_format(buf, ro);
+        if (!drv) {
+            error_report("'%s' invalid format", buf);
+            return NULL;
+        }
     }
 
     /* disk I/O throttling */
@@ -700,12 +705,13 @@ static DriveInfo *blockdev_init(QemuOpts *all_opts,
     }
 
     QINCREF(bs_opts);
-    ret = bdrv_open(dinfo->bdrv, file, bs_opts, bdrv_flags, NULL);
+    ret = bdrv_open(dinfo->bdrv, file, bs_opts, bdrv_flags, drv);
 
     if (ret < 0) {
         if (ret == -EMEDIUMTYPE) {
             error_report("could not open disk image %s: not in %s format",
-                         file ?: dinfo->id, qdict_get_str(bs_opts, "driver"));
+                         file ?: dinfo->id, drv ? drv->format_name :
+                         qdict_get_str(bs_opts, "driver"));
         } else {
             error_report("could not open disk image %s: %s",
                          file ?: dinfo->id, strerror(-ret));