[PATCH v4] scsi: support packing multi-segment in UNMAP command

[Chao Yu <chao@kernel.org>]

As SCSI SBC4 specification section 5.30.2 describes that it can
support unmapping one or more LBA range in single UNMAP command.

However, previously we only pack one LBA range in UNMAP command
by default no matter device gives the block limits that says it
can support unmapping multiple LBA ranges with a single UNMAP
command.

This patch sets max_discard_segments config according to block
limits of device, and supports unmapping multiple LBA ranges with
a single UNMAP command.

Signed-off-by: Chao Yu <chao@kernel.org>
---
v4:
- clean up commit message.
- fix to avoid truncating .max_unmap_block_desc_count during type cast.
- add comments and clean up codes.

 drivers/scsi/sd.c | 35 ++++++++++++++++++++++++-----------
 drivers/scsi/sd.h |  1 +
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 895b56c8f25e..114f61c3ccd3 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -790,6 +790,8 @@ static void sd_config_discard(struct scsi_disk *sdkp, unsigned int mode)
 	q->limits.discard_granularity =
 		max(sdkp->physical_block_size,
 		    sdkp->unmap_granularity * logical_block_size);
+	blk_queue_max_discard_segments(q, min_t(u32, U16_MAX,
+				sdkp->max_unmap_block_desc_count));
 	sdkp->provisioning_mode = mode;
 
 	switch (mode) {
@@ -836,9 +838,10 @@ static blk_status_t sd_setup_unmap_cmnd(struct scsi_cmnd *cmd)
 	struct scsi_device *sdp = cmd->device;
 	struct request *rq = scsi_cmd_to_rq(cmd);
 	struct scsi_disk *sdkp = scsi_disk(rq->q->disk);
-	u64 lba = sectors_to_logical(sdp, blk_rq_pos(rq));
-	u32 nr_blocks = sectors_to_logical(sdp, blk_rq_sectors(rq));
-	unsigned int data_len = 24;
+	unsigned short segments = blk_rq_nr_discard_segments(rq);
+	unsigned int data_len = 8 + 16 * segments;
+	unsigned int descriptor_offset = 8;
+	struct bio *bio;
 	char *buf;
 
 	rq->special_vec.bv_page = mempool_alloc(sd_page_pool, GFP_ATOMIC);
@@ -851,13 +854,20 @@ static blk_status_t sd_setup_unmap_cmnd(struct scsi_cmnd *cmd)
 
 	cmd->cmd_len = 10;
 	cmd->cmnd[0] = UNMAP;
-	cmd->cmnd[8] = 24;
+	cmd->cmnd[8] = data_len;
 
 	buf = bvec_virt(&rq->special_vec);
-	put_unaligned_be16(6 + 16, &buf[0]);
-	put_unaligned_be16(16, &buf[2]);
-	put_unaligned_be64(lba, &buf[8]);
-	put_unaligned_be32(nr_blocks, &buf[16]);
+	put_unaligned_be16(6 + 16 * segments, &buf[0]);
+	put_unaligned_be16(16 * segments, &buf[2]);
+
+	__rq_for_each_bio(bio, rq) {
+		u64 lba = sectors_to_logical(sdp, bio->bi_iter.bi_sector);
+		u32 nr_blocks = sectors_to_logical(sdp, bio_sectors(bio));
+
+		put_unaligned_be64(lba, &buf[descriptor_offset]);
+		put_unaligned_be32(nr_blocks, &buf[descriptor_offset + 8]);
+		descriptor_offset += 16;
+	}
 
 	cmd->allowed = sdkp->max_retries;
 	cmd->transfersize = data_len;
@@ -2862,7 +2872,7 @@ static void sd_read_block_limits(struct scsi_disk *sdkp)
 	sdkp->opt_xfer_blocks = get_unaligned_be32(&vpd->data[12]);
 
 	if (vpd->len >= 64) {
-		unsigned int lba_count, desc_count;
+		unsigned int lba_count;
 
 		sdkp->max_ws_blocks = (u32)get_unaligned_be64(&vpd->data[36]);
 
@@ -2870,9 +2880,12 @@ static void sd_read_block_limits(struct scsi_disk *sdkp)
 			goto out;
 
 		lba_count = get_unaligned_be32(&vpd->data[20]);
-		desc_count = get_unaligned_be32(&vpd->data[24]);
 
-		if (lba_count && desc_count)
+		/* Extract the MAXIMUM UNMAP BLOCK DESCRIPTOR COUNT. */
+		sdkp->max_unmap_block_desc_count =
+					get_unaligned_be32(&vpd->data[24]);
+
+		if (lba_count && sdkp->max_unmap_block_desc_count)
 			sdkp->max_unmap_blocks = lba_count;
 
 		sdkp->unmap_granularity = get_unaligned_be32(&vpd->data[28]);
diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index 5eea762f84d1..e7c51d23395b 100644
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -119,6 +119,7 @@ struct scsi_disk {
 	u32		opt_xfer_blocks;
 	u32		max_ws_blocks;
 	u32		max_unmap_blocks;
+	u32		max_unmap_block_desc_count;
 	u32		unmap_granularity;
 	u32		unmap_alignment;
 	u32		index;
-- 
2.25.1