[PATCH v7 05/11] 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.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 block/monitor/block-hmp-cmds.c |  2 +-
 block/snapshot.c               | 26 +++++++++++++++++++++++---
 include/block/snapshot.h       |  3 ++-
 migration/savevm.c             |  4 ++--
 replay/replay-debugging.c      |  2 +-
 tests/qemu-iotests/267.out     | 12 ++++++------
 6 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index ebb6ae0333..aee243becd 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -901,7 +901,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     SnapshotEntry *snapshot_entry;
     Error *err = NULL;
 
-    bs = bdrv_all_find_vmstate_bs(false, NULL, &err);
+    bs = bdrv_all_find_vmstate_bs(NULL, false, NULL, &err);
     if (!bs) {
         error_report_err(err);
         return;
diff --git a/block/snapshot.c b/block/snapshot.c
index 220173deae..0b129bee8f 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -678,7 +678,9 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
     return 0;
 }
 
-BlockDriverState *bdrv_all_find_vmstate_bs(bool has_devices, strList *devices,
+
+BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
+                                           bool has_devices, strList *devices,
                                            Error **errp)
 {
     g_autoptr(GList) bdrvs = NULL;
@@ -699,13 +701,31 @@ BlockDriverState *bdrv_all_find_vmstate_bs(bool has_devices, strList *devices,
             bdrv_can_snapshot(bs);
         aio_context_release(ctx);
 
-        if (found) {
+        if (vmstate_bs) {
+            if (g_str_equal(vmstate_bs,
+                            bdrv_get_node_name(bs))) {
+                if (found) {
+                    return bs;
+                } else {
+                    error_setg(errp,
+                               "vmstate block device '%s' does not support snapshots",
+                               vmstate_bs);
+                    return NULL;
+                }
+            }
+        } else if (found) {
             return bs;
         }
 
         iterbdrvs = iterbdrvs->next;
     }
 
-    error_setg(errp, "No block device supports snapshots");
+    if (vmstate_bs) {
+        error_setg(errp,
+                   "vmstate block device '%s' does not exist", vmstate_bs);
+    } else {
+        error_setg(errp,
+                   "no block device can store vmstate for snapshot");
+    }
     return NULL;
 }
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 2569a903f2..8a6a37240d 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -95,7 +95,8 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
                              strList *devices,
                              Error **errp);
 
-BlockDriverState *bdrv_all_find_vmstate_bs(bool has_devices, strList *devices,
+BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
+                                           bool has_devices, strList *devices,
                                            Error **errp);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index efbe390671..1ca72e2e71 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2691,7 +2691,7 @@ bool save_snapshot(const char *name, Error **errp)
         }
     }
 
-    bs = bdrv_all_find_vmstate_bs(false, NULL, errp);
+    bs = bdrv_all_find_vmstate_bs(NULL, false, NULL, errp);
     if (bs == NULL) {
         return false;
     }
@@ -2881,7 +2881,7 @@ bool load_snapshot(const char *name, Error **errp)
         return false;
     }
 
-    bs_vm_state = bdrv_all_find_vmstate_bs(false, NULL, errp);
+    bs_vm_state = bdrv_all_find_vmstate_bs(NULL, false, NULL, errp);
     if (!bs_vm_state) {
         return false;
     }
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index a17c1d3578..5262233a5d 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -149,7 +149,7 @@ static char *replay_find_nearest_snapshot(int64_t icount,
 
     *snapshot_icount = -1;
 
-    bs = bdrv_all_find_vmstate_bs(false, NULL, NULL);
+    bs = bdrv_all_find_vmstate_bs(NULL, false, NULL, NULL);
     if (!bs) {
         goto fail;
     }
diff --git a/tests/qemu-iotests/267.out b/tests/qemu-iotests/267.out
index 6149029b25..7176e376e1 100644
--- a/tests/qemu-iotests/267.out
+++ b/tests/qemu-iotests/267.out
@@ -6,11 +6,11 @@ Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
 Testing:
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
-Error: No block device supports snapshots
+Error: no block device can store vmstate for snapshot
 (qemu) info snapshots
-No block device supports snapshots
+no block device can store vmstate for snapshot
 (qemu) loadvm snap0
-Error: No block device supports snapshots
+Error: no block device can store vmstate for snapshot
 (qemu) quit
 
 
@@ -22,7 +22,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
 Error: Device 'none0' is writable but does not support snapshots
 (qemu) info snapshots
-No block device supports snapshots
+no block device can store vmstate for snapshot
 (qemu) loadvm snap0
 Error: Device 'none0' is writable but does not support snapshots
 (qemu) quit
@@ -58,7 +58,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
 Error: Device 'virtio0' is writable but does not support snapshots
 (qemu) info snapshots
-No block device supports snapshots
+no block device can store vmstate for snapshot
 (qemu) loadvm snap0
 Error: Device 'virtio0' is writable but does not support snapshots
 (qemu) quit
@@ -83,7 +83,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
 Error: Device 'file' is writable but does not support snapshots
 (qemu) info snapshots
-No block device supports snapshots
+no block device can store vmstate for snapshot
 (qemu) loadvm snap0
 Error: Device 'file' is writable but does not support snapshots
 (qemu) quit
-- 
2.26.2