Re: [PATCH 3/4] uapi glibc compat: Do not check for __USE_MISC
From: Hauke Mehrtens <hauke@hauke-m.de>
Date: 2017-03-17 18:17:59
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On 03/16/2017 09:26 AM, Mikko Rapeli wrote:
On Thu, Mar 16, 2017 at 07:59:12AM +0000, David Woodhouse wrote:quoted
On Sun, 2017-03-12 at 23:00 +0100, Hauke Mehrtens wrote:quoted
__USE_MISC is glibc specific and not available in musl libc. Only do this check when glibc is used. This fixes a problem with musl libc. ... -/* Coordinate with glibc net/if.h header. */ -#if defined(_NET_IF_H) && defined(__USE_MISC) +/* Coordinate with libc net/if.h header. */ +#if defined(_NET_IF_H) && (!defined(__GLIBC__) || defined(__USE_MISC))I *really* don't like building up a plethora of knowledge about specific libc implementations in the kernel. As a general rule, if we have *anything* that depends on __GLIBC__ then we are Doing It Wrong™.Kernel does not depend on glibc but uapi headers check for some defintions so that userspace code can include both libc and kernel header files without compiler errors. This interface between kernel and libc header files is messy due to long history of copying header files from kernel to libc implementations etc and thus this kind of ifdef magic with in depth knowledge of various libc's defintions is currently unavoidable.
I agree with you David. Should I change my patch? The check for __USE_MISC was added in this commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f0a3fdca794d1e68ae284ef4caefe681f7c18e89 musl does not define it, but still adds the defines which glibc adds when __USE_MISC is set. Hauke