[PATCH v3 5/7] block: allow specifying name of block device for vmstate storage

["Daniel P. Berrangé" <berrange@redhat.com>]

Currently the vmstate will be stored in the first block device that
supports snapshots. Historically this would have usually been the
root device, but with UEFI it might be the variable store. There
needs to be a way to override the choice of block device to store
the state in.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 block/monitor/block-hmp-cmds.c |  2 +-
 block/snapshot.c               | 17 +++++++++++++++--
 include/block/snapshot.h       |  4 +++-
 migration/savevm.c             |  4 ++--
 4 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index db76c43cc2..81d1b52262 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -900,7 +900,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     SnapshotEntry *snapshot_entry;
     Error *err = NULL;
 
-    bs = bdrv_all_find_vmstate_bs(NULL, &err);
+    bs = bdrv_all_find_vmstate_bs(NULL, NULL, &err);
     if (!bs) {
         error_report_err(err);
         return;
diff --git a/block/snapshot.c b/block/snapshot.c
index 5691cdc6cb..1f7b9a5146 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -604,7 +604,9 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
     return 0;
 }
 
-BlockDriverState *bdrv_all_find_vmstate_bs(strList *devices, Error **errp)
+BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
+                                           strList *devices,
+                                           Error **errp)
 {
     g_autoptr(GList) bdrvs = NULL;
     GList *iterbdrvs;
@@ -624,6 +626,13 @@ BlockDriverState *bdrv_all_find_vmstate_bs(strList *devices, Error **errp)
             bdrv_can_snapshot(bs);
         aio_context_release(ctx);
 
+        if (vmstate_bs && g_str_equal(vmstate_bs,
+                                      bdrv_get_node_name(bs))) {
+            error_setg(errp, "block device '%s' does not support snapshots",
+                       vmstate_bs);
+            return NULL;
+        }
+
         if (found) {
             return bs;
         }
@@ -631,6 +640,10 @@ BlockDriverState *bdrv_all_find_vmstate_bs(strList *devices, Error **errp)
         iterbdrvs = iterbdrvs->next;
     }
 
-    error_setg(errp, "No block device supports snapshots");
+    if (vmstate_bs) {
+        error_setg(errp, "Block device '%s' does not exist", vmstate_bs);
+    } else {
+        error_setg(errp, "No block device supports snapshots");
+    }
     return NULL;
 }
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 1c5b0705a9..05550e5da1 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -86,6 +86,8 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
                              strList *devices,
                              Error **errp);
 
-BlockDriverState *bdrv_all_find_vmstate_bs(strList *devices, Error **errp);
+BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
+                                           strList *devices,
+                                           Error **errp);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index ae56de1a85..4a52704132 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2691,7 +2691,7 @@ int save_snapshot(const char *name, Error **errp)
         }
     }
 
-    bs = bdrv_all_find_vmstate_bs(NULL, errp);
+    bs = bdrv_all_find_vmstate_bs(NULL, NULL, errp);
     if (bs == NULL) {
         return ret;
     }
@@ -2881,7 +2881,7 @@ int load_snapshot(const char *name, Error **errp)
         return -1;
     }
 
-    bs_vm_state = bdrv_all_find_vmstate_bs(NULL, errp);
+    bs_vm_state = bdrv_all_find_vmstate_bs(NULL, NULL, errp);
     if (!bs_vm_state) {
         return -1;
     }
-- 
2.26.2