nvme-fc: use nr_phys_segments to determine existence of sgl

For some nvme command, when issued by the nvme core layer, there
is an internal buffer which can cause blk_rq_payload_bytes() to
return a non-zero value yet there is no actual/real command payload
and sg list.  An example is the WRITE ZEROES command.

To address this, when making choices on whether to dma map an sgl,
use blk_rq_nr_phys_segments() instead of blk_rq_payload_bytes().
When there is a sgl, blk_rq_payload_bytes() will return the amount
of data to be transferred by the sgl.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index b29b12498a1a9bb5fa900359b0a9534ceecb8ad9..ba8f2a9cbdaf1ebe265675b4522f1df2a676abf2 100644 (file)
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -2107,7 +2107,7 @@ nvme_fc_map_data(struct nvme_fc_ctrl *ctrl, struct request *rq,
 
        freq->sg_cnt = 0;
 
-       if (!blk_rq_payload_bytes(rq))
+       if (!blk_rq_nr_phys_segments(rq))
                return 0;
 
        freq->sg_table.sgl = freq->first_sgl;
@@ -2304,12 +2304,23 @@ nvme_fc_queue_rq(struct blk_mq_hw_ctx *hctx,
        if (ret)
                return ret;
 
-       data_len = blk_rq_payload_bytes(rq);
-       if (data_len)
+       /*
+        * nvme core doesn't quite treat the rq opaquely. Commands such
+        * as WRITE ZEROES will return a non-zero rq payload_bytes yet
+        * there is no actual payload to be transferred.
+        * To get it right, key data transmission on there being 1 or
+        * more physical segments in the sg list. If there is no
+        * physical segments, there is no payload.
+        */
+       if (blk_rq_nr_phys_segments(rq)) {
+               data_len = blk_rq_payload_bytes(rq);
                io_dir = ((rq_data_dir(rq) == WRITE) ?
                                        NVMEFC_FCP_WRITE : NVMEFC_FCP_READ);
-       else
+       } else {
+               data_len = 0;
                io_dir = NVMEFC_FCP_NODATA;
+       }
+
 
        return nvme_fc_start_fcp_op(ctrl, queue, op, data_len, io_dir);
 }