eventfd: fold eventfd_ctx_read() into eventfd_read()

eventfd_ctx_read() is not used outside of eventfd.c, so unexport it and
fold it into eventfd_read().  This slightly simplifies the code and
makes it more analogous to eventfd_write().

(eventfd_ctx_read() was apparently added years ago for KVM irqfd's, but
was never used.)

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/eventfd.c

@@ -207,36 +207,27 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *w
 }
 EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
 
-/**
- * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
- * @ctx: [in] Pointer to eventfd context.
- * @no_wait: [in] Different from zero if the operation should not block.
- * @cnt: [out] Pointer to the 64-bit counter value.
- *
- * Returns %0 if successful, or the following error codes:
- *
- *  - -EAGAIN      : The operation would have blocked but @no_wait was non-zero.
- *  - -ERESTARTSYS : A signal interrupted the wait operation.
- *
- * If @no_wait is zero, the function might sleep until the eventfd internal
- * counter becomes greater than zero.
- */
-ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
+static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
+			    loff_t *ppos)
 {
+	struct eventfd_ctx *ctx = file->private_data;
 	ssize_t res;
+	__u64 ucnt = 0;
 	DECLARE_WAITQUEUE(wait, current);
 
+	if (count < sizeof(ucnt))
+		return -EINVAL;
+
 	spin_lock_irq(&ctx->wqh.lock);
-	*cnt = 0;
 	res = -EAGAIN;
 	if (ctx->count > 0)
-		res = 0;
-	else if (!no_wait) {
+		res = sizeof(ucnt);
+	else if (!(file->f_flags & O_NONBLOCK)) {
 		__add_wait_queue(&ctx->wqh, &wait);
 		for (;;) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			if (ctx->count > 0) {
-				res = 0;
+				res = sizeof(ucnt);
 				break;
 			}
 			if (signal_pending(current)) {
@@ -250,32 +241,18 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
 		__remove_wait_queue(&ctx->wqh, &wait);
 		__set_current_state(TASK_RUNNING);
 	}
-	if (likely(res == 0)) {
-		eventfd_ctx_do_read(ctx, cnt);
+	if (likely(res > 0)) {
+		eventfd_ctx_do_read(ctx, &ucnt);
 		if (waitqueue_active(&ctx->wqh))
 			wake_up_locked_poll(&ctx->wqh, POLLOUT);
 	}
 	spin_unlock_irq(&ctx->wqh.lock);
 
+	if (res > 0 && put_user(ucnt, (__u64 __user *)buf))
+		return -EFAULT;
+
 	return res;
 }
-EXPORT_SYMBOL_GPL(eventfd_ctx_read);
-
-static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
-			    loff_t *ppos)
-{
-	struct eventfd_ctx *ctx = file->private_data;
-	ssize_t res;
-	__u64 cnt;
-
-	if (count < sizeof(cnt))
-		return -EINVAL;
-	res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
-	if (res < 0)
-		return res;
-
-	return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
-}
 
 static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
 			     loff_t *ppos)

include/linux/eventfd.h

@@ -36,7 +36,6 @@ struct file *eventfd_fget(int fd);
 struct eventfd_ctx *eventfd_ctx_fdget(int fd);
 struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
 __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_entry_t *wait,
 				  __u64 *cnt);
 
@@ -62,12 +61,6 @@ static inline void eventfd_ctx_put(struct eventfd_ctx *ctx)
 
 }
 
-static inline ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait,
-				       __u64 *cnt)
-{
-	return -ENOSYS;
-}
-
 static inline int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx,
 						wait_queue_entry_t *wait, __u64 *cnt)
 {