[PATCH V2 2/2] io_uring: support to inject result for NOP

[Ming Lei <ming.lei@redhat.com>]

Support to inject result for NOP so that we can inject failure from
userspace. It is very helpful for covering failure handling code in
io_uring core change.

With nop flags, it becomes possible to add more test features on NOP in
future.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/uapi/linux/io_uring.h |  8 ++++++++
 io_uring/nop.c                | 26 +++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 922f29b07ccc..21e9cd604068 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -72,6 +72,7 @@ struct io_uring_sqe {
 		__u32		waitid_flags;
 		__u32		futex_flags;
 		__u32		install_fd_flags;
+		__u32		nop_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
@@ -413,6 +414,13 @@ enum io_uring_msg_ring_flags {
  */
 #define IORING_FIXED_FD_NO_CLOEXEC	(1U << 0)
 
+/*
+ * IORING_OP_NOP flags (sqe->nop_flags)
+ *
+ * IORING_NOP_INJECT_RESULT	Inject result from sqe->result
+ */
+#define IORING_NOP_INJECT_RESULT	(1U << 0)
+
 /*
  * IO completion data structure (Completion Queue Entry)
  */
diff --git a/io_uring/nop.c b/io_uring/nop.c
index 1a4e312dfe51..a5bcf3d6984f 100644
--- a/io_uring/nop.c
+++ b/io_uring/nop.c
@@ -10,18 +10,34 @@
 #include "io_uring.h"
 #include "nop.h"
 
+struct io_nop {
+	/* NOTE: kiocb has the file as the first member, so don't do it here */
+	struct file     *file;
+	int             result;
+};
+
 int io_nop_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	if (READ_ONCE(sqe->rw_flags))
+	unsigned int flags;
+	struct io_nop *nop = io_kiocb_to_cmd(req, struct io_nop);
+
+	flags = READ_ONCE(sqe->nop_flags);
+	if (flags & ~IORING_NOP_INJECT_RESULT)
 		return -EINVAL;
+
+	if (flags & IORING_NOP_INJECT_RESULT)
+		nop->result = READ_ONCE(sqe->len);
+	else
+		nop->result = 0;
 	return 0;
 }
 
-/*
- * IORING_OP_NOP just posts a completion event, nothing else.
- */
 int io_nop(struct io_kiocb *req, unsigned int issue_flags)
 {
-	io_req_set_res(req, 0, 0);
+	struct io_nop *nop = io_kiocb_to_cmd(req, struct io_nop);
+
+	if (nop->result < 0)
+		req_set_fail(req);
+	io_req_set_res(req, nop->result, 0);
 	return IOU_OK;
 }
-- 
2.42.0