[V9,05/14] block: add snapshot info query function bdrv_query_snapshot_info_list()

diff --git a/block/qapi.c b/block/qapi.c
index 51692d3..2da28db 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -14,29 +14,53 @@ 
 #include "block/qapi.h"
 #include "block/block_int.h"
 
-void bdrv_collect_snapshots(BlockDriverState *bs , ImageInfo *info)
+/* return 0 on success, and @p_list will be set only on success. */
+int bdrv_query_snapshot_info_list(BlockDriverState *bs,
+                                  SnapshotInfoList **p_list,
+                                  Error **errp)
 {
     int i, sn_count;
     QEMUSnapshotInfo *sn_tab = NULL;
-    SnapshotInfoList *info_list, *cur_item = NULL;
+    SnapshotInfoList *info_list, *cur_item = NULL, *head = NULL;
+    SnapshotInfo *info;
+
     sn_count = bdrv_snapshot_list(bs, &sn_tab);
+    if (sn_count < 0) {
+        const char *dev = bdrv_get_device_name(bs);
+        switch (sn_count) {
+        case -ENOMEDIUM:
+            error_setg(errp, "Device '%s' is not inserted", dev);
+            break;
+        case -ENOTSUP:
+            error_setg(errp,
+                       "Device '%s' does not support internal snapshots",
+                       dev);
+            break;
+        default:
+            error_setg(errp, "Can't list snapshots of device '%s': %s",
+                       dev, strerror(-sn_count));
+            break;
+        }
+        return sn_count;
+    }
 
     for (i = 0; i < sn_count; i++) {
-        info->has_snapshots = true;
-        info_list = g_new0(SnapshotInfoList, 1);
 
-        info_list->value                = g_new0(SnapshotInfo, 1);
-        info_list->value->id            = g_strdup(sn_tab[i].id_str);
-        info_list->value->name          = g_strdup(sn_tab[i].name);
-        info_list->value->vm_state_size = sn_tab[i].vm_state_size;
-        info_list->value->date_sec      = sn_tab[i].date_sec;
-        info_list->value->date_nsec     = sn_tab[i].date_nsec;
-        info_list->value->vm_clock_sec  = sn_tab[i].vm_clock_nsec / 1000000000;
-        info_list->value->vm_clock_nsec = sn_tab[i].vm_clock_nsec % 1000000000;
+        info = g_new0(SnapshotInfo, 1);
+        info->id            = g_strdup(sn_tab[i].id_str);
+        info->name          = g_strdup(sn_tab[i].name);
+        info->vm_state_size = sn_tab[i].vm_state_size;
+        info->date_sec      = sn_tab[i].date_sec;
+        info->date_nsec     = sn_tab[i].date_nsec;
+        info->vm_clock_sec  = sn_tab[i].vm_clock_nsec / 1000000000;
+        info->vm_clock_nsec = sn_tab[i].vm_clock_nsec % 1000000000;
+
+        info_list = g_new0(SnapshotInfoList, 1);
+        info_list->value = info;
 
         /* XXX: waiting for the qapi to support qemu-queue.h types */
         if (!cur_item) {
-            info->snapshots = cur_item = info_list;
+            head = cur_item = info_list;
         } else {
             cur_item->next = info_list;
             cur_item = info_list;
@@ -45,6 +69,8 @@  void bdrv_collect_snapshots(BlockDriverState *bs , ImageInfo *info)
     }
 
     g_free(sn_tab);
+    *p_list = head;
+    return 0;
 }
 
 void bdrv_collect_image_info(BlockDriverState *bs,
diff --git a/include/block/qapi.h b/include/block/qapi.h
index ecb5242..4b46165 100644
--- a/include/block/qapi.h
+++ b/include/block/qapi.h
@@ -17,7 +17,9 @@ 
 #include "qapi-types.h"
 #include "block/block.h"
 
-void bdrv_collect_snapshots(BlockDriverState *bs , ImageInfo *info);
+int bdrv_query_snapshot_info_list(BlockDriverState *bs,
+                                  SnapshotInfoList **p_list,
+                                  Error **errp);
 void bdrv_collect_image_info(BlockDriverState *bs,
                              ImageInfo *info,
                              const char *filename);
diff --git a/qemu-img.c b/qemu-img.c
index 2e1698f..cb534c9 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1735,7 +1735,9 @@  static ImageInfoList *collect_image_info_list(const char *filename,
 
         info = g_new0(ImageInfo, 1);
         bdrv_collect_image_info(bs, info, filename);
-        bdrv_collect_snapshots(bs, info);
+        if (!bdrv_query_snapshot_info_list(bs, &info->snapshots, NULL)) {
+            info->has_snapshots = true;
+        }
 
         elem = g_new0(ImageInfoList, 1);
         elem->value = info;