[PATCH] bsg: deprecate BIDI support in bsg

[Christoph Hellwig <hch@lst.de>]

Besides the OSD command set that never got traction, the only SCSI
command using bidirectional buffers is XDWRITEREAD in the 10 and 32
byte variants, which is extremely esoteric.  It probably doesn't make
sense to keep the support code around just for that, so start
deprecating the support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/bsg.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/bsg.c b/block/bsg.c
index 9a442c23a715..60b41bf79e16 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -177,6 +177,10 @@ bsg_map_hdr(struct request_queue *q, struct sg_io_v4 *hdr, fmode_t mode)
 			goto out;
 		}
 
+		pr_warn_once(
+			"BIDI support in bsg has been deprecated and might be removed. "
+			"Please report your use case to linux-scsi@vger.kernel.org\n");
+
 		next_rq = blk_get_request(q, REQ_OP_SCSI_IN, 0);
 		if (IS_ERR(next_rq)) {
 			ret = PTR_ERR(next_rq);
-- 
2.19.2