eventfd: change int to __u64 in eventfd_signal()

eventfd_ctx->count is an __u64 counter which is allowed to reach
ULLONG_MAX.  eventfd_write() adds a __u64 value to "count", but the kernel
side eventfd_signal() only adds an int value to it.  Make them consistent.

[akpm@linux-foundation.org: update interface documentation]
Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventfd.c

@@ -46,20 +46,16 @@ struct eventfd_ctx {
  * value, and we signal this as overflow condition by returining a POLLERR
  * to poll(2).
  *
- * Returns @n in case of success, a non-negative number lower than @n in case
- * of overflow, or the following error codes:
- *
- * -EINVAL    : The value of @n is negative.
+ * Returns the amount by which the counter was incrememnted.  This will be less
+ * than @n if the counter has overflowed.
  */
-int eventfd_signal(struct eventfd_ctx *ctx, int n)
+__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
 {
 	unsigned long flags;
 
-	if (n < 0)
-		return -EINVAL;
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
 	if (ULLONG_MAX - ctx->count < n)
-		n = (int) (ULLONG_MAX - ctx->count);
+		n = ULLONG_MAX - ctx->count;
 	ctx->count += n;
 	if (waitqueue_active(&ctx->wqh))
 		wake_up_locked_poll(&ctx->wqh, POLLIN);

include/linux/eventfd.h

@@ -34,7 +34,7 @@ void eventfd_ctx_put(struct eventfd_ctx *ctx);
 struct file *eventfd_fget(int fd);
 struct eventfd_ctx *eventfd_ctx_fdget(int fd);
 struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
-int eventfd_signal(struct eventfd_ctx *ctx, int n);
+__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n);
 ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt);
 int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
 				  __u64 *cnt);