blockdev: Fix drive_del not to crash when drive is not in use

Watch this:

    (qemu) drive_add 0 if=none,file=tmp.img
    OK
    (qemu) info block
    none0: type=hd removable=0 file=tmp.img ro=0 drv=raw encrypted=0
    (qemu) drive_del none0
    Segmentation fault (core dumped)

do_drive_del()'s code to clean up the pointer from a qdev using the
drive back to the drive needs to check whether such a device exists.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/blockdev.c b/blockdev.c
index 0621390..f7f591f 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -687,13 +687,15 @@ int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
 
     /* clean up guest state from pointing to host resource by
      * finding and removing DeviceState "drive" property */
-    for (prop = bs->peer->info->props; prop && prop->name; prop++) {
-        if (prop->info->type == PROP_TYPE_DRIVE) {
-            ptr = qdev_get_prop_ptr(bs->peer, prop);
-            if ((*ptr) == bs) {
-                bdrv_detach(bs, bs->peer);
-                *ptr = NULL;
-                break;
+    if (bs->peer) {
+        for (prop = bs->peer->info->props; prop && prop->name; prop++) {
+            if (prop->info->type == PROP_TYPE_DRIVE) {
+                ptr = qdev_get_prop_ptr(bs->peer, prop);
+                if (*ptr == bs) {
+                    bdrv_detach(bs, bs->peer);
+                    *ptr = NULL;
+                    break;
+                }
             }
         }
     }