[PATCH for-next v4 2/4] io_uring: introduce fixed buffer support for io_uring_cmd

[Kanchan Joshi <joshi.k@xxxxxxxxxxx>]

From: Anuj Gupta <anuj20.g@xxxxxxxxxxx>

Add IORING_URING_CMD_FIXED flag that is to be used for sending io_uring
command with previously registered buffers. User-space passes the buffer
index in sqe->buf_index, same as done in read/write variants that uses
fixed buffers.

Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
---
 include/linux/io_uring.h      |  3 ++-
 include/uapi/linux/io_uring.h |  9 +++++++++
 io_uring/uring_cmd.c          | 18 +++++++++++++++++-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index dba6fb47aa6c..6ca633b88816 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -16,6 +16,7 @@ enum io_uring_cmd_flags {
 	IO_URING_F_SQE128		= 4,
 	IO_URING_F_CQE32		= 8,
 	IO_URING_F_IOPOLL		= 16,
+	IO_URING_F_FIXEDBUFS		= 32,
 };
 
 struct io_uring_cmd {
@@ -28,7 +29,7 @@ struct io_uring_cmd {
 		void *cookie;
 	};
 	u32		cmd_op;
-	u32		pad;
+	u32		flags;
 	u8		pdu[32]; /* available inline for free use */
 };
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 48e5c70e0baf..34be8dd31f17 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -56,6 +56,7 @@ struct io_uring_sqe {
 		__u32		hardlink_flags;
 		__u32		xattr_flags;
 		__u32		msg_ring_flags;
+		__u32		uring_cmd_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
@@ -219,6 +220,14 @@ enum io_uring_op {
 	IORING_OP_LAST,
 };
 
+/*
+ * sqe->uring_cmd_flags
+ * IORING_URING_CMD_FIXED	use registered buffer; pass thig flag
+ *				along with setting sqe->buf_index.
+ */
+#define IORING_URING_CMD_FIXED	(1U << 0)
+
+
 /*
  * sqe->fsync_flags
  */
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 8cddd18ad10b..ea989a348d98 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -3,6 +3,7 @@
 #include <linux/errno.h>
 #include <linux/file.h>
 #include <linux/io_uring.h>
+#include <linux/nospec.h>
 
 #include <uapi/linux/io_uring.h>
 
@@ -76,8 +77,21 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
 
-	if (sqe->rw_flags || sqe->__pad1)
+	if (sqe->__pad1)
 		return -EINVAL;
+
+	ioucmd->flags = READ_ONCE(sqe->uring_cmd_flags);
+	req->buf_index = READ_ONCE(sqe->buf_index);
+	if (ioucmd->flags & IORING_URING_CMD_FIXED) {
+		struct io_ring_ctx *ctx = req->ctx;
+		u16 index;
+
+		if (unlikely(req->buf_index >= ctx->nr_user_bufs))
+			return -EFAULT;
+		index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
+		req->imu = ctx->user_bufs[index];
+		io_req_set_rsrc_node(req, ctx, 0);
+	}
 	ioucmd->cmd = sqe->cmd;
 	ioucmd->cmd_op = READ_ONCE(sqe->cmd_op);
 	return 0;
@@ -102,6 +116,8 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 		req->iopoll_completed = 0;
 		WRITE_ONCE(ioucmd->cookie, NULL);
 	}
+	if (ioucmd->flags & IORING_URING_CMD_FIXED)
+		issue_flags |= IO_URING_F_FIXEDBUFS;
 
 	if (req_has_async_data(req))
 		ioucmd->cmd = req->async_data;
-- 
2.25.1