block: Always abort reopen after prepare succeeded

bdrv_reopen_multiple() does not invoke bdrv_reopen_abort() for the
element of the reopen queue for which bdrv_reopen_prepare() failed,
because it assumes that the prepare function will have rolled back all
changes already.

However, bdrv_reopen_prepare() does not do this in every case: It may
notice an error after BlockDriver.bdrv_reopen_prepare() succeeded, and
it will not invoke BlockDriver.bdrv_reopen_abort() then; and neither
will bdrv_reopen_multiple(), as explained above.

This is wrong because we must always call .bdrv_reopen_commit() or
.bdrv_reopen_abort() after .bdrv_reopen_prepare() has succeeded.
Otherwise, the block driver has no chance to undo what it has done in
its implementation of .bdrv_reopen_prepare().

To fix this, bdrv_reopen_prepare() has to call .bdrv_reopen_abort() if
it wants to return an error after .bdrv_reopen_prepare() has succeeded.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -3201,6 +3201,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
     QDict *orig_reopen_opts;
     char *discard = NULL;
     bool read_only;
+    bool drv_prepared = false;
 
     assert(reopen_state != NULL);
     assert(reopen_state->bs->drv != NULL);
@@ -3285,6 +3286,8 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
         goto error;
     }
 
+    drv_prepared = true;
+
     /* Options that are not handled are only okay if they are unchanged
      * compared to the old state. It is expected that some options are only
      * used for the initial open, but not reopen (e.g. filename) */
@@ -3350,6 +3353,15 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
     reopen_state->options = qobject_ref(orig_reopen_opts);
 
 error:
+    if (ret < 0 && drv_prepared) {
+        /* drv->bdrv_reopen_prepare() has succeeded, so we need to
+         * call drv->bdrv_reopen_abort() before signaling an error
+         * (bdrv_reopen_multiple() will not call bdrv_reopen_abort()
+         * when the respective bdrv_reopen_prepare() has failed) */
+        if (drv->bdrv_reopen_abort) {
+            drv->bdrv_reopen_abort(reopen_state);
+        }
+    }
     qemu_opts_del(opts);
     qobject_unref(orig_reopen_opts);
     g_free(discard);