scst_vdisk: Add XCOPY support in blkdev handler

scst/src/dev_handlers/scst_vdisk.c

@@ -6430,6 +6430,49 @@ static void vdisk_task_mgmt_fn_done(struct scst_mgmt_cmd *mcmd,
 	return;
 }
 
+static void vdisk_bio_ext_copy_remap(struct scst_cmd *cmd,
+	struct scst_ext_copy_seg_descr *seg)
+{
+	struct block_device *in_bdev, *out_bdev;
+	loff_t pos_in, pos_out;
+	size_t len, ret;
+	struct scst_vdisk_dev *src_virt_dev = vdev_find(seg->src_tgt_dev->dev->virt_name);
+	struct scst_vdisk_dev *dst_virt_dev = vdev_find(seg->dst_tgt_dev->dev->virt_name);
+	uint64_t in_bdev_size, out_bdev_size;
+
+	if (!src_virt_dev || !dst_virt_dev || !seg) {
+		return;
+	}
+
+	in_bdev = src_virt_dev->bdev_desc.bdev;
+	out_bdev = dst_virt_dev->bdev_desc.bdev;
+	pos_in = seg->data_descr.src_lba << seg->src_tgt_dev->dev->block_shift;
+	pos_out = seg->data_descr.dst_lba << seg->dst_tgt_dev->dev->block_shift;
+	len = seg->data_descr.data_len;
+	in_bdev_size = bdev_nr_bytes(in_bdev);
+	out_bdev_size = bdev_nr_bytes(out_bdev);
+
+	if (len <= 4096 || (pos_in + len > in_bdev_size) ||
+	    (pos_out + len > out_bdev_size)) {
+		return;
+	}
+
+	//TODO: Adjust size/offsets w.r.t block device block size
+	if (bdev_max_copy_sectors(in_bdev)) {
+		ret = blkdev_copy_offload(in_bdev, pos_in, pos_out, len,
+					     NULL, NULL, GFP_KERNEL, out_bdev);
+		if (ret >= len) {
+			scst_ext_copy_remap_done(cmd, NULL, 0);
+			return;
+		}
+	}
+
+	/*
+	 * Fallback to default SCST write path
+	 */
+	scst_ext_copy_remap_done(cmd, &seg->data_descr, 1);
+}
+
 #ifdef CONFIG_DEBUG_EXT_COPY_REMAP
 static void vdev_ext_copy_remap(struct scst_cmd *cmd,
 	struct scst_ext_copy_seg_descr *seg)
@@ -9746,6 +9789,7 @@ static struct scst_dev_type vdisk_blk_devtype = {
 	.del_device =		vdisk_del_device,
 	.dev_attrs =		vdisk_blockio_attrs,
 	.add_device_parameters = blockio_add_dev_params,
+	.ext_copy_remap =	vdisk_bio_ext_copy_remap,
 #if defined(CONFIG_SCST_DEBUG) || defined(CONFIG_SCST_TRACING)
 	.default_trace_flags =	SCST_DEFAULT_DEV_LOG_FLAGS,
 	.trace_flags =		&trace_flag,