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

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Message-ID: <CA+FuTSdifgNAYe4DAfpRJxCO08y-sOi=XhOeMhd9mKbA3aPOug@mail.gmail.com>
Date:   Mon, 16 Nov 2020 12:00:48 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        linux-fsdevel@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Soheil Hassas Yeganeh <soheil.kdev@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Shuo Chen <shuochen@...gle.com>
Subject: Re: [PATCH v2] epoll: add nsec timeout support

On Mon, Nov 16, 2020 at 11:19 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> 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

Thanks. Good point, I'll add that in v3.