[PATCH v2 05/10] block: add emulation for copy

[Nitesh Shetty <nj.shetty@xxxxxxxxxxx>]

For the devices which does not support copy, copy emulation is
added. Copy-emulation is implemented by reading from source ranges
into memory and writing to the corresponding destination synchronously.

TODO: Optimise emulation.

Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
---
 block/blk-lib.c | 119 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 3ae2c27b566e..05c8cd02fffc 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -272,6 +272,65 @@ int blk_copy_offload(struct block_device *src_bdev, int nr_srcs,
 	return cio_await_completion(cio);
 }
 
+int blk_submit_rw_buf(struct block_device *bdev, void *buf, sector_t buf_len,
+				sector_t sector, unsigned int op, gfp_t gfp_mask)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+	struct bio *bio, *parent = NULL;
+	sector_t max_hw_len = min_t(unsigned int, queue_max_hw_sectors(q),
+			queue_max_segments(q) << (PAGE_SHIFT - SECTOR_SHIFT)) << SECTOR_SHIFT;
+	sector_t len, remaining;
+	int ret;
+
+	for (remaining = buf_len; remaining > 0; remaining -= len) {
+		len = min_t(int, max_hw_len, remaining);
+retry:
+		bio = bio_map_kern(q, buf, len, gfp_mask);
+		if (IS_ERR(bio)) {
+			len >>= 1;
+			if (len)
+				goto retry;
+			return PTR_ERR(bio);
+		}
+
+		bio->bi_iter.bi_sector = sector >> SECTOR_SHIFT;
+		bio->bi_opf = op;
+		bio_set_dev(bio, bdev);
+		bio->bi_end_io = NULL;
+		bio->bi_private = NULL;
+
+		if (parent) {
+			bio_chain(parent, bio);
+			submit_bio(parent);
+		}
+		parent = bio;
+		sector += len;
+		buf = (char *) buf + len;
+	}
+	ret = submit_bio_wait(bio);
+	bio_put(bio);
+
+	return ret;
+}
+
+static void *blk_alloc_buf(sector_t req_size, sector_t *alloc_size, gfp_t gfp_mask)
+{
+	int min_size = PAGE_SIZE;
+	void *buf;
+
+	while (req_size >= min_size) {
+		buf = kvmalloc(req_size, gfp_mask);
+		if (buf) {
+			*alloc_size = req_size;
+			return buf;
+		}
+		/* retry half the requested size */
+		req_size >>= 1;
+	}
+
+	return NULL;
+}
+
 static inline int blk_copy_sanity_check(struct block_device *src_bdev,
 		struct block_device *dst_bdev, struct range_entry *rlist, int nr)
 {
@@ -297,6 +356,64 @@ static inline int blk_copy_sanity_check(struct block_device *src_bdev,
 	return 0;
 }
 
+static inline sector_t blk_copy_max_range(struct range_entry *rlist, int nr, sector_t *max_len)
+{
+	int i;
+	sector_t len = 0;
+
+	*max_len = 0;
+	for (i = 0; i < nr; i++) {
+		*max_len = max(*max_len, rlist[i].len);
+		len += rlist[i].len;
+	}
+
+	return len;
+}
+
+/*
+ * If native copy offload feature is absent, this function tries to emulate,
+ * by copying data from source to a temporary buffer and from buffer to
+ * destination device.
+ */
+static int blk_copy_emulate(struct block_device *src_bdev, int nr,
+		struct range_entry *rlist, struct block_device *dest_bdev, gfp_t gfp_mask)
+{
+	void *buf = NULL;
+	int ret, nr_i = 0;
+	sector_t src, dst, copy_len, buf_len, read_len, copied_len, max_len = 0, remaining = 0;
+
+	copy_len = blk_copy_max_range(rlist, nr, &max_len);
+	buf = blk_alloc_buf(max_len, &buf_len, gfp_mask);
+	if (!buf)
+		return -ENOMEM;
+
+	for (copied_len = 0; copied_len < copy_len; copied_len += read_len) {
+		if (!remaining) {
+			rlist[nr_i].comp_len = 0;
+			src = rlist[nr_i].src;
+			dst = rlist[nr_i].dst;
+			remaining = rlist[nr_i++].len;
+		}
+
+		read_len = min_t(sector_t, remaining, buf_len);
+		ret = blk_submit_rw_buf(src_bdev, buf, read_len, src, REQ_OP_READ, gfp_mask);
+		if (ret)
+			goto out;
+		src += read_len;
+		remaining -= read_len;
+		ret = blk_submit_rw_buf(dest_bdev, buf, read_len, dst, REQ_OP_WRITE,
+				gfp_mask);
+		if (ret)
+			goto out;
+		else
+			rlist[nr_i - 1].comp_len += read_len;
+		dst += read_len;
+	}
+out:
+	kvfree(buf);
+	return ret;
+}
+
 static inline bool blk_check_copy_offload(struct request_queue *src_q,
 		struct request_queue *dest_q)
 {
@@ -346,6 +463,8 @@ int blkdev_issue_copy(struct block_device *src_bdev, int nr,
 
 	if (blk_check_copy_offload(src_q, dest_q))
 		ret = blk_copy_offload(src_bdev, nr, rlist, dest_bdev, gfp_mask);
+	else
+		ret = blk_copy_emulate(src_bdev, nr, rlist, dest_bdev, gfp_mask);
 
 	return ret;
 }
-- 
2.30.0-rc0