ublk: don't call ublk_dispatch_req() for NEED_GET_DATA

ublk_dispatch_req() currently handles 3 different cases: incoming ublk
requests that don't need to wait for a data buffer, incoming requests
that do need to wait for a buffer, and resuming those requests once the
buffer is provided. But the call site that provides a data buffer
(UBLK_IO_NEED_GET_DATA) is separate from those for incoming requests.

So simplify the function by splitting the UBLK_IO_NEED_GET_DATA case
into its own function ublk_get_data(). This avoids several redundant
checks in the UBLK_IO_NEED_GET_DATA case, and streamlines the incoming
request cases.

Don't call ublk_fill_io_cmd() for UBLK_IO_NEED_GET_DATA, as it's no
longer necessary to set io->cmd or the UBLK_IO_FLAG_ACTIVE flag for
ublk_dispatch_req().

Since UBLK_IO_NEED_GET_DATA no longer relies on ublk_dispatch_req()
calling io_uring_cmd_done(), return the UBLK_IO_RES_OK status directly
from the ->uring_cmd() handler. If ublk_start_io() fails, don't complete
the UBLK_IO_NEED_GET_DATA command, matching the existing behavior.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250430225234.2676781-8-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: calebsander

drivers/block/ublk_drv.c

@@ -1212,25 +1212,12 @@ static void ublk_dispatch_req(struct ublk_queue *ubq,
 		 * so immediately pass UBLK_IO_RES_NEED_GET_DATA to ublksrv
 		 * and notify it.
 		 */
-		if (!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA)) {
-			io->flags |= UBLK_IO_FLAG_NEED_GET_DATA;
-			pr_devel("%s: need get data. qid %d tag %d io_flags %x\n",
-					__func__, ubq->q_id, req->tag, io->flags);
-			ublk_complete_io_cmd(io, UBLK_IO_RES_NEED_GET_DATA,
-					     issue_flags);
-			return;
-		}
-		/*
-		 * We have handled UBLK_IO_NEED_GET_DATA command,
-		 * so clear UBLK_IO_FLAG_NEED_GET_DATA now and just
-		 * do the copy work.
-		 */
-		io->flags &= ~UBLK_IO_FLAG_NEED_GET_DATA;
-		/* update iod->addr because ublksrv may have passed a new io buffer */
-		ublk_get_iod(ubq, req->tag)->addr = io->addr;
-		pr_devel("%s: update iod->addr: qid %d tag %d io_flags %x addr %llx\n",
-				__func__, ubq->q_id, req->tag, io->flags,
-				ublk_get_iod(ubq, req->tag)->addr);
+		io->flags |= UBLK_IO_FLAG_NEED_GET_DATA;
+		pr_devel("%s: need get data. qid %d tag %d io_flags %x\n",
+				__func__, ubq->q_id, req->tag, io->flags);
+		ublk_complete_io_cmd(io, UBLK_IO_RES_NEED_GET_DATA,
+				     issue_flags);
+		return;
 	}
 
 	if (!ublk_start_io(ubq, req, io))
@@ -2045,6 +2032,24 @@ static int ublk_commit_and_fetch(const struct ublk_queue *ubq,
 	return 0;
 }
 
+static bool ublk_get_data(const struct ublk_queue *ubq, struct ublk_io *io,
+			  struct request *req)
+{
+	/*
+	 * We have handled UBLK_IO_NEED_GET_DATA command,
+	 * so clear UBLK_IO_FLAG_NEED_GET_DATA now and just
+	 * do the copy work.
+	 */
+	io->flags &= ~UBLK_IO_FLAG_NEED_GET_DATA;
+	/* update iod->addr because ublksrv may have passed a new io buffer */
+	ublk_get_iod(ubq, req->tag)->addr = io->addr;
+	pr_devel("%s: update iod->addr: qid %d tag %d io_flags %x addr %llx\n",
+			__func__, ubq->q_id, req->tag, io->flags,
+			ublk_get_iod(ubq, req->tag)->addr);
+
+	return ublk_start_io(ubq, req, io);
+}
+
 static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 			       unsigned int issue_flags,
 			       const struct ublksrv_io_cmd *ub_cmd)
@@ -2110,10 +2115,12 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 	case UBLK_IO_NEED_GET_DATA:
 		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
 			goto out;
-		ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
+		io->addr = ub_cmd->addr;
 		req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);
-		ublk_dispatch_req(ubq, req, issue_flags);
-		return -EIOCBQUEUED;
+		if (!ublk_get_data(ubq, io, req))
+			return -EIOCBQUEUED;
+
+		return UBLK_IO_RES_OK;
 	default:
 		goto out;
 	}