monitor: make 'info snapshots' show only fully available snapshots

The output generated by 'info snapshots' shows only snapshots that exist on the
block device that saves the VM state. This output can cause an user to
erroneously try to load an snapshot that is not available on all block devices.

$ qemu-img snapshot -l xxtest.qcow2
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1                                1.5M 2010-07-26 16:51:52   00:00:08.599
2                                1.5M 2010-07-26 16:51:53   00:00:09.719
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763

$ qemu-img snapshot -l xxtest2.qcow2
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
3                                   0 2010-07-26 17:26:49   00:00:13.245
4                                   0 2010-07-26 19:01:00   00:00:46.763

Current output:
$ qemu -hda xxtest.qcow2 -hdb xxtest2.qcow2 -monitor stdio -vnc :0
QEMU 0.12.4 monitor - type 'help' for more information
(qemu) info snapshots
Snapshot devices: ide0-hd0
Snapshot list (from ide0-hd0):
ID        TAG                 VM SIZE                DATE       VM CLOCK
1                                1.5M 2010-07-26 16:51:52   00:00:08.599
2                                1.5M 2010-07-26 16:51:53   00:00:09.719
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763

Snapshots 1 and 2 do not exist on xxtest2.qcow, but they are displayed anyway.

This patch sumarizes the output to only show fully available snapshots.

New output:
(qemu) info snapshots
ID        TAG                 VM SIZE                DATE       VM CLOCK
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763
Signed-off-by: NMiguel Di Ciurcio Filho <miguel.filho@gmail.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

savevm.c

@@ -2039,8 +2039,10 @@ void do_delvm(Monitor *mon, const QDict *qdict)
 void do_info_snapshots(Monitor *mon)
 {
     BlockDriverState *bs, *bs1;
-    QEMUSnapshotInfo *sn_tab, *sn;
-    int nb_sns, i;
+    QEMUSnapshotInfo *sn_tab, *sn, s, *sn_info = &s;
+    int nb_sns, i, ret, available;
+    int total;
+    int *available_snapshots;
     char buf[256];
 
     bs = bdrv_snapshots();
@@ -2048,27 +2050,52 @@ void do_info_snapshots(Monitor *mon)
         monitor_printf(mon, "No available block device supports snapshots\n");
         return;
     }
-    monitor_printf(mon, "Snapshot devices:");
-    bs1 = NULL;
-    while ((bs1 = bdrv_next(bs1))) {
-        if (bdrv_can_snapshot(bs1)) {
-            if (bs == bs1)
-                monitor_printf(mon, " %s", bdrv_get_device_name(bs1));
-        }
-    }
-    monitor_printf(mon, "\n");
 
     nb_sns = bdrv_snapshot_list(bs, &sn_tab);
     if (nb_sns < 0) {
         monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
         return;
     }
-    monitor_printf(mon, "Snapshot list (from %s):\n",
-                   bdrv_get_device_name(bs));
-    monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
-    for(i = 0; i < nb_sns; i++) {
+
+    if (nb_sns == 0) {
+        monitor_printf(mon, "There is no snapshot available.\n");
+        return;
+    }
+
+    available_snapshots = qemu_mallocz(sizeof(int) * nb_sns);
+    total = 0;
+    for (i = 0; i < nb_sns; i++) {
         sn = &sn_tab[i];
-        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
+        available = 1;
+        bs1 = NULL;
+
+        while ((bs1 = bdrv_next(bs1))) {
+            if (bdrv_can_snapshot(bs1) && bs1 != bs) {
+                ret = bdrv_snapshot_find(bs1, sn_info, sn->id_str);
+                if (ret < 0) {
+                    available = 0;
+                    break;
+                }
+            }
+        }
+
+        if (available) {
+            available_snapshots[total] = i;
+            total++;
+        }
     }
+
+    if (total > 0) {
+        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
+        for (i = 0; i < total; i++) {
+            sn = &sn_tab[available_snapshots[i]];
+            monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
+        }
+    } else {
+        monitor_printf(mon, "There is no suitable snapshot available\n");
+    }
+
     qemu_free(sn_tab);
+    qemu_free(available_snapshots);
+
 }