centos man page for eventfd_ctx_read

EVENTFD_CTX_READ(9)					  Events based on file descripto				       EVENTFD_CTX_READ(9)

NAME
       eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.

SYNOPSIS
       ssize_t eventfd_ctx_read(struct eventfd_ctx * ctx, int no_wait, __u64 * cnt);

ARGUMENTS
       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.

DESCRIPTION
       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.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						       EVENTFD_CTX_READ(9)