Date: Sat, 8 Jul 2017 16:27:28 -0400 From: Felix Janda <felix.janda@...teo.de> To: Carlos O'Donell <carlos@...hat.com> Cc: Hauke Mehrtens <hauke@...ke-m.de>, musl@...ts.openwall.com, linux-kernel@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, linux-api@...r.kernel.org Subject: Re: Re: [PATCH resent] uapi libc compat: allow non-glibc to opt out of uapi definitions Carlos O'Donell wrote: > 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. >From the beginning, this patch was CCed to linux-api. Let me repost anyway with a new (hopefully clearer) commit message. > 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. This patch does not change anything for glibc (or uclibc), it just, in a not very intrusive way, improves the situation for any other libc. Felix
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