io_uring: ensure we return -EINVAL on unknown opcode

If we submit an unknown opcode and have fd == -1, io_op_needs_file()
will return true as we default to needing a file. Then when we go and
assign the file, we find the 'fd' invalid and return -EBADF. We really
should be returning -EINVAL for that case, as we normally do for
unsupported opcodes.

Change io_op_needs_file() to have the following return values:

0   - does not need a file
1   - does need a file
< 0 - error value

and use this to pass back the right value for this invalid case.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/uapi/linux/io_uring.h

@@ -58,23 +58,28 @@ struct io_uring_sqe {
 #define IORING_SETUP_SQ_AFF	(1U << 2)	/* sq_thread_cpu is valid */
 #define IORING_SETUP_CQSIZE	(1U << 3)	/* app defines CQ size */
 
-#define IORING_OP_NOP		0
-#define IORING_OP_READV		1
-#define IORING_OP_WRITEV	2
-#define IORING_OP_FSYNC		3
-#define IORING_OP_READ_FIXED	4
-#define IORING_OP_WRITE_FIXED	5
-#define IORING_OP_POLL_ADD	6
-#define IORING_OP_POLL_REMOVE	7
-#define IORING_OP_SYNC_FILE_RANGE	8
-#define IORING_OP_SENDMSG	9
-#define IORING_OP_RECVMSG	10
-#define IORING_OP_TIMEOUT	11
-#define IORING_OP_TIMEOUT_REMOVE	12
-#define IORING_OP_ACCEPT	13
-#define IORING_OP_ASYNC_CANCEL	14
-#define IORING_OP_LINK_TIMEOUT	15
-#define IORING_OP_CONNECT	16
+enum {
+	IORING_OP_NOP,
+	IORING_OP_READV,
+	IORING_OP_WRITEV,
+	IORING_OP_FSYNC,
+	IORING_OP_READ_FIXED,
+	IORING_OP_WRITE_FIXED,
+	IORING_OP_POLL_ADD,
+	IORING_OP_POLL_REMOVE,
+	IORING_OP_SYNC_FILE_RANGE,
+	IORING_OP_SENDMSG,
+	IORING_OP_RECVMSG,
+	IORING_OP_TIMEOUT,
+	IORING_OP_TIMEOUT_REMOVE,
+	IORING_OP_ACCEPT,
+	IORING_OP_ASYNC_CANCEL,
+	IORING_OP_LINK_TIMEOUT,
+	IORING_OP_CONNECT,
+
+	/* this goes last, obviously */
+	IORING_OP_LAST,
+};
 
 /*
  * sqe->fsync_flags