linux-kernel - Re: [PATCH v2] epoll: add nsec timeout support

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Message-ID: <20201116161930.GF29991@casper.infradead.org>
Date:   Mon, 16 Nov 2020 16:19:30 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        soheil.kdev@...il.com, arnd@...db.de, shuochen@...gle.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH v2] epoll: add nsec timeout support

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