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

On Sun, Aug 06, 2017 at 05:42:13PM -0400, Willem de Bruijn wrote:

On Sun, Aug 6, 2017 at 5:33 PM, Mikko Rapeli [off-list ref] wrote:

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On Sun, Aug 06, 2017 at 05:24:20PM -0400, Willem de Bruijn wrote:

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+#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?

Okay. Or feel free to include it in the patchset if that helps resolve
dependencies.

If you don't have the time, I will send tomorrow a new version of this
patch which fixes the commit topic and before that your libc-compat.h change
so both could be applied together.

Feel free to be faster :)

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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?

I'm still afraid that this patch as is will break builds that include
<linux/time.h> first.

I agree, but I also want uapi headers to cleanly compile. I know this might
break stuff on userspace side which rely on these broken header file
dependencies, but if the fix to just re-order include
statements I'm fine with it, also when the complaints hit my inbox.

If I had the CPU time, memory and disk space, I'd do a full yocto distro
build to see how badly userspace could break but I don't at home.

-Mikko