[RFC PATCH 5/6] io_uring: add support for uring_cmd with fixed-buffer

[Kanchan Joshi <joshi.k@xxxxxxxxxxx>]

From: Anuj Gupta <anuj20.g@xxxxxxxxxxx>

Add IORING_OP_URING_CMD_FIXED opcode that enables performing the
operation with previously registered buffers.

Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
---
 fs/io_uring.c                 | 27 ++++++++++++++++++++++++++-
 include/uapi/linux/io_uring.h |  6 +++++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1f2263a78c8e..a80f4c98ea86 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1060,6 +1060,10 @@ static const struct io_op_def io_op_defs[] = {
 		.needs_file		= 1,
 		.offsets		= 1,
 	},
+	[IORING_OP_URING_CMD_FIXED] = {
+		.needs_file		= 1,
+		.offsets		= 1,
+	},
 };
 
 static bool io_disarm_next(struct io_kiocb *req);
@@ -3602,7 +3606,12 @@ static int io_uring_cmd_prep(struct io_kiocb *req,
 	}
 
 	cmd->op = READ_ONCE(csqe->op);
-	cmd->len = READ_ONCE(csqe->len);
+	if (req->opcode == IORING_OP_URING_CMD_FIXED) {
+		req->imu = NULL;
+		io_req_set_rsrc_node(req);
+		req->buf_index = READ_ONCE(csqe->buf_index);
+	} else
+		cmd->len = READ_ONCE(csqe->len);
 
 	/*
 	 * The payload is the last 40 bytes of an io_uring_cmd_sqe, with the
@@ -3617,6 +3626,20 @@ static int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 	struct file *file = req->file;
 	int ret;
 
+	if (req->opcode == IORING_OP_URING_CMD_FIXED) {
+		u32 index, buf_index = req->buf_index;
+		struct io_ring_ctx *ctx = req->ctx;
+		struct io_mapped_ubuf *imu = req->imu;
+
+		if (likely(!imu)) {
+			if (unlikely(buf_index >= ctx->nr_user_bufs))
+				return -EFAULT;
+			index = array_index_nospec(buf_index, ctx->nr_user_bufs);
+			imu = READ_ONCE(ctx->user_bufs[index]);
+			req->imu = imu;
+		}
+	}
+
 	ret = file->f_op->uring_cmd(&req->uring_cmd, issue_flags);
 	/* queued async, consumer will call io_uring_cmd_done() when complete */
 	if (ret == -EIOCBQUEUED)
@@ -6031,6 +6054,7 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	case IORING_OP_UNLINKAT:
 		return io_unlinkat_prep(req, sqe);
 	case IORING_OP_URING_CMD:
+	case IORING_OP_URING_CMD_FIXED:
 		return io_uring_cmd_prep(req, sqe);
 	}
 
@@ -6322,6 +6346,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 		ret = io_unlinkat(req, issue_flags);
 		break;
 	case IORING_OP_URING_CMD:
+	case IORING_OP_URING_CMD_FIXED:
 		ret = io_uring_cmd(req, issue_flags);
 		break;
 	default:
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 92565e17bfd9..1a10ebd4ca0a 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -75,7 +75,10 @@ struct io_uring_cmd_sqe {
 	__u64			user_data;
 	__u16			op;
 	__u16			personality;
-	__u32			len;
+	union {
+		__u32			len;
+		__u16			buf_index;
+	};
 	__u64			pdu[5];
 };
 
@@ -154,6 +157,7 @@ enum {
 	IORING_OP_RENAMEAT,
 	IORING_OP_UNLINKAT,
 	IORING_OP_URING_CMD,
+	IORING_OP_URING_CMD_FIXED,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
-- 
2.25.1