linux-kernel - Re: [PATCH v06 18/36] uapi linux/errqueue.h: include linux/time.h in user space

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Message-ID: <20170806213330.GA31101@lakka.kapsi.fi>
Date:   Mon, 7 Aug 2017 00:33:30 +0300
From:   Mikko Rapeli <mikko.rapeli@....fi>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH v06 18/36] uapi linux/errqueue.h: include linux/time.h in
 user space

On Sun, Aug 06, 2017 at 05:24:20PM -0400, Willem de Bruijn wrote:
> >> > +#ifdef __KERNEL__
> >> > +#include <linux/time.h>
> >> > +#else
> >> > +#include <time.h>
> >> > +#endif /* __KERNEL__ */
> >>
> >> This will break applications that include <linux/time.h> manually.
> >> I previously sent a patch to use libc-compat to make compilation succeed
> >> when both are included in the case where <linux/time.h> is included after
> >> <time.h>.
> >>
> >>   https://lkml.org/lkml/2016/9/12/872
> >>
> >> The inverse will require changes to the libc header to avoid redefining
> >> symbols already defined by <linux/time.h>
> >>
> >> The second patch in that 2-patch set included <linux/time.h>
> >> unconditionally after the fix. This broke builds that also included
> >> <time.h> in the wrong order. I did not resubmit the first patch as a
> >> stand-alone, as it is not sufficient to avoid breakage.
> >
> > I wasn't aware of your change, but I was about to send this to fix the
> > case when glibc <time.h> is included before <linux/time.h>:
> >
> > https://github.com/mcfrisk/linux/commit/f3952a27b8a21c6478d26e6246055383483f6a66
> 
> There are a few differences between the two. Including <time.h> does not
> unconditionally define all the symbols. Some are conditional on additional
> state, such as __timespec_defined.

Yep, your patch seems better for libc-compat.h. Could you send it again?

> > but you also ran into problems where <linux/time.h> is included before
> > <time.h> which need fixes in libc header side.
> >
> > So how to proceed with these?
> 
> The libc-compat change is a good fix that can be submitted on its own.

Yes, please do so.

> > I don't like leaving a few dozen non-compiling header files into uapi.
> 
> I agree, but I do not see a simple solution.
> 
> Unless libc has the analogous change, including either <time.h> or
> <linux/time.h> in userspace can unfortunately cause breakage.
> 
> The added include if __KERNEL__ is defined should be safe, though.

Yes, for the kernel side, but your libc-compat change would nice for
userspace, where something will break for sure, but providing source
API compatibility is sometimes impossible.

To summarize, this change from me, and your libc-compat.c for time.h, or?

-Mikko