EFD_SEMAPHORE
*cnt = ((ctx->flags & EFD_SEMAPHORE) && ctx->count) ? 1 : ctx->count;
!!(ctx->flags & EFD_SEMAPHORE));
BUILD_BUG_ON(EFD_SEMAPHORE != (1 << 0));
#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
#ifndef EFD_SEMAPHORE
fd = sys_eventfd2(0, EFD_SEMAPHORE);
fd = sys_eventfd2(0, EFD_SEMAPHORE|EFD_NONBLOCK);