linux-kernel - Re: [musl] Re: [PATCH resent] uapi libc compat: allow non-glibc to opt out of uapi definitions

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Message-ID: <d7624df0-0ea4-aba1-f862-9bac540c972f@redhat.com>
Date:   Tue, 25 Apr 2017 08:13:15 -0400
From:   Carlos O'Donell <carlos@...hat.com>
To:     Hauke Mehrtens <hauke@...ke-m.de>, musl@...ts.openwall.com,
        Felix Janda <felix.janda@...teo.de>,
        linux-kernel@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>, linux-api@...r.kernel.org
Subject: Re: [musl] Re: [PATCH resent] uapi libc compat: allow non-glibc to
 opt out of uapi definitions

On 04/25/2017 02:37 AM, Hauke Mehrtens wrote:
> 
> 
> On 03/08/2017 01:46 PM, David Woodhouse wrote:
>> On Fri, 2016-11-11 at 07:08 -0500, Felix Janda wrote:
>>> Currently, libc-compat.h detects inclusion of specific glibc headers,
>>> and defines corresponding _UAPI_DEF_* macros, which in turn are used in
>>> uapi headers to prevent definition of conflicting structures/constants.
>>> There is no such detection for other c libraries, for them the
>>> _UAPI_DEF_* macros are always defined as 1, and so none of the possibly
>>> conflicting definitions are suppressed.
>>>
>>> This patch enables non-glibc c libraries to request the suppression of
>>> any specific interface by defining the corresponding _UAPI_DEF_* macro
>>> as 0.
>>
>> Ick. It's fairly horrid for kernel headers to be reacting to __GLIBC__
>> in any way. That's just wrong.
>>
>> It makes more sense for C libraries to define the __UAPI_DEF_xxx for
>> themselves as and when they add their own support for certain things,
>> and for the kernel not to have incestuous knowledge of them.
>>
>> The part you add here in the #else /* !__GLIBC__ */ part is what we
>> should do at *all* times.
>>
>> I understand that we'll want to grandfather in the glibc horridness,
>> but let's make it clear that that's what it is, by letting it set the
>> appropriate __UAPI_DEF_xxx macros to zero, and then continue through to
>> your new part. Something like this (incremental to yours):
> 
> Felix's and this change and are looking better than my patches here:
> https://lkml.org/lkml/2017/3/12/235
> 
> Is someone working on brining this into the mainline kernel?
> 
> Is it correct that only the comments should be improved?
> musl only supports including the musl header files before the kernel
> anyway, I assume that it is not needed to make the kernel uapi code
> support also the other order.

Please repost to linux-api so other relevant C library authors can review
the changes and comment on how they might be harmonized.

Whether or not you  support both inclusion orders, kernel first, or libc first,
is a property of your libc implementation.

Today glibc aims to support both inclusion orders since we see applications
with either order, and the ordering should not matter in this case. You either
get one or the other without needing to know any special rules about header
ordering.

-- 
Cheers,
Carlos.