snapshot: create helper to test that block drivers supports snapshots

The patch enforces proper locking for this operation. Signed-off-by: Denis V. Lunev <den@openvz.org> Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> CC: Kevin Wolf <kwolf@redhat.com> Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
qemu · Nov 19, 2015 · e9ff957 · e9ff957
1 parent 5df5416
commit e9ff957
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Showing 3 changed files with 36 additions and 13 deletions.
diff --git a/block/snapshot.c b/block/snapshot.c
@@ -356,3 +356,27 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
 
     return ret;
 }
+
+
+/* Group operations. All block drivers are involved.
+ * These functions will properly handle dataplane (take aio_context_acquire
+ * when appropriate for appropriate block drivers) */
+
+bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
+{
+    bool ok = true;
+    BlockDriverState *bs = NULL;
+
+    while (ok && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bdrv_is_inserted(bs) && !bdrv_is_read_only(bs)) {
+            ok = bdrv_can_snapshot(bs);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return ok;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
@@ -75,4 +75,12 @@ int bdrv_snapshot_load_tmp(BlockDriverState *bs,
 int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
                                          const char *id_or_name,
                                          Error **errp);
+
+
+/* Group operations. All block drivers are involved.
+ * These functions will properly handle dataplane (take aio_context_acquire
+ * when appropriate for appropriate block drivers */
+
+bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
+
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
@@ -1958,19 +1958,10 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     const char *name = qdict_get_try_str(qdict, "name");
     Error *local_err = NULL;
 
-    /* Verify if there is a device that doesn't support snapshots and is writable */
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-
-        if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
-            continue;
-        }
-
-        if (!bdrv_can_snapshot(bs)) {
-            monitor_printf(mon, "Device '%s' is writable but does not support snapshots.\n",
-                               bdrv_get_device_name(bs));
-            return;
-        }
+    if (!bdrv_all_can_snapshot(&bs)) {
+        monitor_printf(mon, "Device '%s' is writable but does not "
+                       "support snapshots.\n", bdrv_get_device_name(bs));
+        return;
     }
 
     bs = find_vmstate_bs();