error: Use error_prepend() where it makes obvious sense

Done with this Coccinelle semantic patch

    @@
    expression FMT, E1, E2;
    expression list ARGS;
    @@
    -    error_setg(E1, FMT, ARGS, error_get_pretty(E2));
    +    error_propagate(E1, E2);/*###*/
    +    error_prepend(E1, FMT/*@@@*/, ARGS);

followed by manual cleanup, first because I can't figure out how to
make Coccinelle transform strings, and second to get rid of now
superfluous error_propagate().

We now use or propagate the original error whole instead of just its
message obtained with error_get_pretty().  This avoids suppressing its
hint (see commit 50b7b00), but I can't see how the errors touched in
this commit could come with hints.  It also improves the message
printed with &error_abort when we screw up (see commit 1e9b65b).

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

block.c

@@ -1349,12 +1349,10 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     ret = bdrv_open_inherit(&backing_hd,
                             *backing_filename ? backing_filename : NULL,
                             reference, options, 0, bs, &child_backing,
-                            &local_err);
+                            errp);
     if (ret < 0) {
         bs->open_flags |= BDRV_O_NO_BACKING;
-        error_setg(errp, "Could not open backing file: %s",
-                   error_get_pretty(local_err));
-        error_free(local_err);
+        error_prepend(errp, "Could not open backing file: ");
         goto free_exit;
     }
 
@@ -1460,12 +1458,11 @@ int bdrv_append_temp_snapshot(BlockDriverState *bs, int flags, Error **errp)
     opts = qemu_opts_create(bdrv_qcow2.create_opts, NULL, 0,
                             &error_abort);
     qemu_opt_set_number(opts, BLOCK_OPT_SIZE, total_size, &error_abort);
-    ret = bdrv_create(&bdrv_qcow2, tmp_filename, opts, &local_err);
+    ret = bdrv_create(&bdrv_qcow2, tmp_filename, opts, errp);
     qemu_opts_del(opts);
     if (ret < 0) {
-        error_setg(errp, "Could not create temporary overlay '%s': %s",
-                   tmp_filename, error_get_pretty(local_err));
-        error_free(local_err);
+        error_prepend(errp, "Could not create temporary overlay '%s': ",
+                      tmp_filename);
         goto out;
     }
 
@@ -3729,9 +3726,9 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
     if (!QLIST_EMPTY(&bs->op_blockers[op])) {
         blocker = QLIST_FIRST(&bs->op_blockers[op]);
         if (errp) {
-            error_setg(errp, "Node '%s' is busy: %s",
-                       bdrv_get_device_or_node_name(bs),
-                       error_get_pretty(blocker->reason));
+            *errp = error_copy(blocker->reason);
+            error_prepend(errp, "Node '%s' is busy: ",
+                          bdrv_get_device_or_node_name(bs));
         }
         return true;
     }

block/qcow2.c

@@ -1762,9 +1762,8 @@ static void qcow2_invalidate_cache(BlockDriverState *bs, Error **errp)
     ret = qcow2_open(bs, options, flags, &local_err);
     QDECREF(options);
     if (local_err) {
-        error_setg(errp, "Could not reopen qcow2 layer: %s",
-                   error_get_pretty(local_err));
-        error_free(local_err);
+        error_propagate(errp, local_err);
+        error_prepend(errp, "Could not reopen qcow2 layer: ");
         return;
     } else if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not reopen qcow2 layer");

block/qed.c

@@ -1611,9 +1611,8 @@ static void bdrv_qed_invalidate_cache(BlockDriverState *bs, Error **errp)
     memset(s, 0, sizeof(BDRVQEDState));
     ret = bdrv_qed_open(bs, NULL, bs->open_flags, &local_err);
     if (local_err) {
-        error_setg(errp, "Could not reopen qed layer: %s",
-                   error_get_pretty(local_err));
-        error_free(local_err);
+        error_propagate(errp, local_err);
+        error_prepend(errp, "Could not reopen qed layer: ");
         return;
     } else if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not reopen qed layer");

hw/block/dataplane/virtio-blk.c

@@ -142,7 +142,6 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
                                   Error **errp)
 {
     VirtIOBlockDataPlane *s;
-    Error *local_err = NULL;
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 
@@ -163,11 +162,8 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
     /* If dataplane is (re-)enabled while the guest is running there could be
      * block jobs that can conflict.
      */
-    if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE,
-                          &local_err)) {
-        error_setg(errp, "cannot start dataplane thread: %s",
-                   error_get_pretty(local_err));
-        error_free(local_err);
+    if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
+        error_prepend(errp, "cannot start dataplane thread: ");
         return;
     }
 

hw/scsi/vhost-scsi.c

@@ -217,11 +217,9 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
     }
 
     if (vs->conf.vhostfd) {
-        vhostfd = monitor_fd_param(cur_mon, vs->conf.vhostfd, &err);
+        vhostfd = monitor_fd_param(cur_mon, vs->conf.vhostfd, errp);
         if (vhostfd == -1) {
-            error_setg(errp, "vhost-scsi: unable to parse vhostfd: %s",
-                       error_get_pretty(err));
-            error_free(err);
+            error_prepend(errp, "vhost-scsi: unable to parse vhostfd: ");
             return;
         }
     } else {

hw/usb/bus.c

@@ -329,9 +329,9 @@ static USBDevice *usb_try_create_simple(USBBus *bus, const char *name,
     }
     object_property_set_bool(OBJECT(dev), true, "realized", &err);
     if (err) {
-        error_setg(errp, "Failed to initialize USB device '%s': %s",
-                   name, error_get_pretty(err));
-        error_free(err);
+        error_propagate(errp, err);
+        error_prepend(errp, "Failed to initialize USB device '%s': ",
+                      name);
         object_unparent(OBJECT(dev));
         return NULL;
     }