Re: [PATCH v2] epoll: add nsec timeout support

[Matthew Wilcox]

On Mon, Nov 16, 2020 at 11:10:01AM -0500, Willem de Bruijn wrote:
> diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
> index 8a3432d0f0dc..f6ef9c9f8ac2 100644
> --- a/include/uapi/linux/eventpoll.h
> +++ b/include/uapi/linux/eventpoll.h
> @@ -21,6 +21,7 @@
>  
>  /* Flags for epoll_create1.  */
>  #define EPOLL_CLOEXEC O_CLOEXEC
> +#define EPOLL_NSTIMEO 0x1
>  
>  /* Valid opcodes to issue to sys_epoll_ctl() */
>  #define EPOLL_CTL_ADD 1

Not a problem with your patch, but this concerns me.  O_CLOEXEC is
defined differently for each architecture, so we need to stay out of
several different bits when we define new flags for EPOLL_*.  Maybe
this:

/*
 * Flags for epoll_create1.  O_CLOEXEC may be different bits, depending
 * on the CPU architecture.  Reserve the known ones.
 */
#define EPOLL_CLOEXEC		O_CLOEXEC
#define EPOLL_RESERVED_FLAGS	0x00680000
#define EPOLL_NSTIMEO		0x00000001