+/*
+ * Add new bs contents at the top of an image chain while the chain is
+ * live, while keeping required fields on the top layer.
+ *
+ * This will modify the BlockDriverState fields, and swap contents
+ * between bs_new and bs_top. Both bs_new and bs_top are modified.
+ *
+ * bs_new is required to be anonymous.
+ *
+ * This function does not create any image files.
+ */
+void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top)
+{
+ BlockDriverState tmp;
+
+ /* bs_new must be anonymous */
+ assert(bs_new->device_name[0] == '\0');
+
+ tmp = *bs_new;
+
+ /* there are some fields that need to stay on the top layer: */
+
+ /* dev info */
+ tmp.dev_ops = bs_top->dev_ops;
+ tmp.dev_opaque = bs_top->dev_opaque;
+ tmp.dev = bs_top->dev;
+ tmp.buffer_alignment = bs_top->buffer_alignment;
+ tmp.copy_on_read = bs_top->copy_on_read;
+
+ /* i/o timing parameters */
+ tmp.slice_time = bs_top->slice_time;
+ tmp.slice_start = bs_top->slice_start;
+ tmp.slice_end = bs_top->slice_end;
+ tmp.io_limits = bs_top->io_limits;
+ tmp.io_base = bs_top->io_base;
+ tmp.throttled_reqs = bs_top->throttled_reqs;
+ tmp.block_timer = bs_top->block_timer;
+ tmp.io_limits_enabled = bs_top->io_limits_enabled;
+
+ /* geometry */
+ tmp.cyls = bs_top->cyls;
+ tmp.heads = bs_top->heads;
+ tmp.secs = bs_top->secs;
+ tmp.translation = bs_top->translation;
+
+ /* r/w error */
+ tmp.on_read_error = bs_top->on_read_error;
+ tmp.on_write_error = bs_top->on_write_error;
+
+ /* i/o status */
+ tmp.iostatus_enabled = bs_top->iostatus_enabled;
+ tmp.iostatus = bs_top->iostatus;
+
+ /* keep the same entry in bdrv_states */
+ pstrcpy(tmp.device_name, sizeof(tmp.device_name), bs_top->device_name);
+ tmp.list = bs_top->list;
+
+ /* The contents of 'tmp' will become bs_top, as we are
+ * swapping bs_new and bs_top contents. */
+ tmp.backing_hd = bs_new;
+ pstrcpy(tmp.backing_file, sizeof(tmp.backing_file), bs_top->filename);
+ bdrv_get_format(bs_top, tmp.backing_format, sizeof(tmp.backing_format));
+
+ /* swap contents of the fixed new bs and the current top */
+ *bs_new = *bs_top;
+ *bs_top = tmp;
+
+ /* device_name[] was carried over from the old bs_top. bs_new
+ * shouldn't be in bdrv_states, so we need to make device_name[]
+ * reflect the anonymity of bs_new
+ */
+ bs_new->device_name[0] = '\0';
+
+ /* clear the copied fields in the new backing file */
+ bdrv_detach_dev(bs_new, bs_new->dev);
+
+ qemu_co_queue_init(&bs_new->throttled_reqs);
+ memset(&bs_new->io_base, 0, sizeof(bs_new->io_base));
+ memset(&bs_new->io_limits, 0, sizeof(bs_new->io_limits));
+ bdrv_iostatus_disable(bs_new);
+
+ /* we don't use bdrv_io_limits_disable() for this, because we don't want
+ * to affect or delete the block_timer, as it has been moved to bs_top */
+ bs_new->io_limits_enabled = false;
+ bs_new->block_timer = NULL;
+ bs_new->slice_time = 0;
+ bs_new->slice_start = 0;
+ bs_new->slice_end = 0;
+}
+