block: push error reporting into bdrv_all_*_snapshot functions

The bdrv_all_*_snapshot functions return a BlockDriverState pointer
for the invalid backend, which the callers then use to report an
error message. In some cases multiple callers are reporting the
same error message, but with slightly different text. In the future
there will be more error scenarios for some of these methods, which
will benefit from fine grained error message reporting. So it is
helpful to push error reporting down a level.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
[PMD: Initialize variables]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210204124834.774401-2-berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index afd75ab628..9532d085ea 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -900,10 +900,11 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
 
     ImageEntry *image_entry, *next_ie;
     SnapshotEntry *snapshot_entry;
+    Error *err = NULL;
 
-    bs = bdrv_all_find_vmstate_bs();
+    bs = bdrv_all_find_vmstate_bs(&err);
     if (!bs) {
-        monitor_printf(mon, "No available block device supports snapshots\n");
+        error_report_err(err);
         return;
     }
     aio_context = bdrv_get_aio_context(bs);
@@ -953,7 +954,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     total = 0;
     for (i = 0; i < nb_sns; i++) {
         SnapshotEntry *next_sn;
-        if (bdrv_all_find_snapshot(sn_tab[i].name, &bs1) == 0) {
+        if (bdrv_all_find_snapshot(sn_tab[i].name, NULL) == 0) {
             global_snapshots[total] = i;
             total++;
             QTAILQ_FOREACH(image_entry, &image_list, next) {