eventfd: add a uapi header for eventfd userspace APIs

Create a uapi header include/uapi/linux/eventfd.h, move the associated
flags to the uapi header, and include it from linux/eventfd.h.

Suggested-by: Christian Brauner <[e-mail]>
Signed-off-by: Wen Yang <[e-mail]>
Reviewed-by: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Dylan Yudaken <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Eric Biggers <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Message-Id: <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

include/linux/eventfd.h

···
 #ifndef _LINUX_EVENTFD_H
 #define _LINUX_EVENTFD_H
 
-#include <linux/fcntl.h>
 #include <linux/wait.h>
 #include <linux/err.h>
 #include <linux/percpu-defs.h>
 #include <linux/percpu.h>
 #include <linux/sched.h>
+#include <uapi/linux/eventfd.h>
 
 /*
  * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
···
  * from eventfd, in order to leave a free define-space for
  * shared O_* flags.
  */
-#define EFD_SEMAPHORE (1 << 0)
-#define EFD_CLOEXEC O_CLOEXEC
-#define EFD_NONBLOCK O_NONBLOCK
-
 #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
 #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
 

include/uapi/linux/eventfd.h

···
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_EVENTFD_H
+#define _UAPI_LINUX_EVENTFD_H
+
+#include <linux/fcntl.h>
+
+#define EFD_SEMAPHORE (1 << 0)
+#define EFD_CLOEXEC O_CLOEXEC
+#define EFD_NONBLOCK O_NONBLOCK
+
+#endif /* _UAPI_LINUX_EVENTFD_H */