On 8/11/23 03:52, Nitesh Shetty wrote:

+ * Description:
+ *	Copy source offset to destination offset within block device, using
+ *	device's native copy offload feature.

Offloading the copy operation is not guaranteed so I think that needs to 
be reflected in the above comment.

+ *	We perform copy operation by sending 2 bio's.
+ *	1. We take a plug and send a REQ_OP_COPY_SRC bio along with source
+ *	sector and length. Once this bio reaches request layer, we form a
+ *	request and wait for dst bio to arrive.

What will happen if the queue depth of the request queue at the bottom 
is one?

+		blk_start_plug(&plug);
+		dst_bio = blk_next_bio(src_bio, bdev, 0, REQ_OP_COPY_DST, gfp);

blk_next_bio() can return NULL so its return value should be checked.

+		dst_bio->bi_iter.bi_size = chunk;
+		dst_bio->bi_iter.bi_sector = pos_out >> SECTOR_SHIFT;
+		dst_bio->bi_end_io = blkdev_copy_offload_dst_endio;
+		dst_bio->bi_private = offload_io;

Thanks,

Bart.