io_uring: add support for canceling timeout requests

We might have cases where the need for a specific timeout is gone, add
support for canceling an existing timeout operation. This works like the
POLL_REMOVE command, where the application passes in the user_data of
the timeout it wishes to cancel in the sqe->addr field.

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

include/uapi/linux/io_uring.h

@@ -64,6 +64,7 @@ struct io_uring_sqe {
 #define IORING_OP_SENDMSG	9
 #define IORING_OP_RECVMSG	10
 #define IORING_OP_TIMEOUT	11
+#define IORING_OP_TIMEOUT_REMOVE	12
 
 /*
  * sqe->fsync_flags