Subject: Re: [musl] Re: [PATCH resent] uapi libc compat: allow non-glibc to
 opt out of uapi definitions
To: musl@lists.openwall.com, David Woodhouse <dwmw2@infradead.org>,
        Felix Janda <felix.janda@posteo.de>, linux-kernel@vger.kernel.org
References: <20161111120820.GA435@nyan>
 <1488977188.4347.134.camel@infradead.org>
 <459a8faf-4585-5063-3d94-3a1fecfa8289@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>, linux-api@vger.kernel.org
From: Hauke Mehrtens <hauke@hauke-m.de>
Message-ID: <21e624b9-7ab1-dcf9-fb1e-c31dd564a283@hauke-m.de>
Date: Tue, 25 Apr 2017 08:45:43 +0200
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On 03/08/2017 05:39 PM, Carlos O'Donell wrote:
> Any header needing compat with a libc includes libc-compat.h (per the 
> documented way the model works). With this patch any included linux kernel
> header that also includes libc-compat.h would immediately define all 
> the __UAPI_DEF_* constants to 1 as-if it had defined those structures, 
> but it has not.
> 
> For example, with these two patches applied, the inclusion of linux/if.h
> would define __UAPI_DEF_XATTR to 1, but linux/if.h has not defined
> XATTR_CREATE or other constants, so a subsequent inclusion sys/xattrs.h
> from userspace would _not_ define XATTR_CREATE because __UAPI_DEF_XATTR set
> to 1 indicates the kernel has.
> 
> I don't want to read into the model you are proposing and would rather you
> document the semantics clearly so we can all see what you mean.

What about moving the code from libc-comapt.h into the specific header
files? This way including linux/if.h would not have an impact on
__UAPI_DEF_XATTR, because this is defined in linux/xattr.h. We would
still have a problem when the specific Linux header file gets included
before the libc header file, but at least musl does not support this anyway.

Hauke