linux-kernel - Re: [musl] [PATCHv2] uapi libc compat: add fallback for unsupported libcs

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Message-ID: <20170708214402.GA2742@nyan>
Date:   Sat, 8 Jul 2017 17:44:02 -0400
From:   Felix Janda <felix.janda@...teo.de>
To:     musl@...ts.openwall.com
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Carlos O'Donell <carlos@...hat.com>
Subject: Re: [musl] [PATCHv2] uapi libc compat: add fallback for unsupported
 libcs

Hauke Mehrtens wrote:
> 
> 
> On 07/08/2017 10:27 PM, Felix Janda wrote:
> > libc-compat.h aims to prevent symbol collisions between uapi and libc
> > headers for each supported libc. This requires continuous coordination
> > between them.
> > 
> > The goal of this commit is to improve the situation for libcs (such as
> > musl) which are not yet supported and/or do not wish to be explicitly
> > supported, while not affecting supported libcs. More precisely, with
> > this commit, unsupported libcs can request the suppression of any
> > specific uapi definition by defining the correspondings _UAPI_DEF_*
> > macro as 0. This can fix symbol collisions for them, as long as the
> > libc headers are included before the uapi headers. Inclusion in the
> > other order is outside the scope of this commit.
> > 
> > All infrastructure in order to enable this fallback for unsupported
> > libcs is already in place, except that libc-compat.h unconditionally
> > defines all _UAPI_DEF_* macros to 1 for all unsupported libcs so that
> > any previous definitions are ignored. In order to fix this, this commit
> > merely makes these definitions conditional.
> > 
> > This commit together with the musl libc commit
> > 
> > http://git.musl-libc.org/cgit/musl/commit/?id=04983f2272382af92eb8f8838964ff944fbb8258
> > 
> > fixes for example the following compiler errors when <linux/in6.h> is
> > included after musl's <netinet/in.h>:
> > 
> > ./linux/in6.h:32:8: error: redefinition of 'struct in6_addr'
> > ./linux/in6.h:49:8: error: redefinition of 'struct sockaddr_in6'
> > ./linux/in6.h:59:8: error: redefinition of 'struct ipv6_mreq'
> > 
> > Signed-off-by: Felix Janda <felix.janda@...teo.de>
> > Acked-by: Rich Felker <dalias@...c.org>
> > ---
> > v2: The only change to the previous version is the commit title and
> >     message.
> > ---
> >  include/uapi/linux/libc-compat.h | 52 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 52 insertions(+)
> 
> Does the documentation at the top of this file need some updates?

I think that at least the comment preceding the part touched by this
patch should be updated. I'm not sure how to update the documentation
on top -- it does not say anything about unsupported libcs.

> > diff --git a/include/uapi/linux/libc-compat.h b/include/uapi/linux/libc-compat.h
> > index 44b8a6b..c316725 100644
> > --- a/include/uapi/linux/libc-compat.h
> > +++ b/include/uapi/linux/libc-compat.h
> > @@ -171,42 +171,94 @@
> >  #else /* !defined(__GLIBC__) */
> 
> Why don't you used #ifndef ?

It seemed more consistent with the rest of the file, which also uses
"#if defined(...)" instead of "#ifdef". On the other hand, there are
two uses of "#ifndef" in the file. I do not have any strong opinion on
this.

> >  /* Definitions for if.h */
> > +#if !defined(__UAPI_DEF_IF_IFCONF)
> >  #define __UAPI_DEF_IF_IFCONF 1
> > +#endif
> > +#if !defined(__UAPI_DEF_IF_IFMAP)
> >  #define __UAPI_DEF_IF_IFMAP 1
> > +#endif
> > +#if !defined(__UAPI_DEF_IFNAMSIZ)
> 
> This should be:
> #if !defined( __UAPI_DEF_IF_IFNAMSIZ)
> 
> >  #define __UAPI_DEF_IF_IFNAMSIZ 1
> > +#endif
> > +#if !defined(__UAPI_DEF_IFREQ)
> 
> This should be:
> #if !defined(__UAPI_DEF_IF_IFREQ)

Thanks! Will be fixed in the next version.

Felix

> >  #define __UAPI_DEF_IF_IFREQ 1
> > +#endif
> >  /* Everything up to IFF_DYNAMIC, matches net/if.h until glibc 2.23 */
> > +#if !defined(__UAPI_DEF_IF_NET_DEVICE_FLAGS)
> >  #define __UAPI_DEF_IF_NET_DEVICE_FLAGS 1
> > +#endif
> >  /* For the future if glibc adds IFF_LOWER_UP, IFF_DORMANT and IFF_ECHO */
> > +#if !defined(__UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO)
> >  #define __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO 1
> > +#endif
> >  
> >  /* Definitions for in.h */
> > +#if !defined(__UAPI_DEF_IN_ADDR)
> >  #define __UAPI_DEF_IN_ADDR		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IN_IPPROTO)
> >  #define __UAPI_DEF_IN_IPPROTO		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IN_PKTINFO)
> >  #define __UAPI_DEF_IN_PKTINFO		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IP_MREQ)
> >  #define __UAPI_DEF_IP_MREQ		1
> > +#endif
> > +#if !defined(__UAPI_DEF_SOCKADDR_IN)
> >  #define __UAPI_DEF_SOCKADDR_IN		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IN_CLASS)
> >  #define __UAPI_DEF_IN_CLASS		1
> > +#endif
> >  
> >  /* Definitions for in6.h */
> > +#if !defined(__UAPI_DEF_IN6_ADDR)
> >  #define __UAPI_DEF_IN6_ADDR		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IN6_ADDR_ALT)
> >  #define __UAPI_DEF_IN6_ADDR_ALT		1
> > +#endif
> > +#if !defined(__UAPI_DEF_SOCKADDR_IN6)
> >  #define __UAPI_DEF_SOCKADDR_IN6		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPV6_MREQ)
> >  #define __UAPI_DEF_IPV6_MREQ		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPPROTO_V6)
> >  #define __UAPI_DEF_IPPROTO_V6		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPV6_OPTIONS)
> >  #define __UAPI_DEF_IPV6_OPTIONS		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IN6_PKTINFO)
> >  #define __UAPI_DEF_IN6_PKTINFO		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IP6_MTUINFO)
> >  #define __UAPI_DEF_IP6_MTUINFO		1
> > +#endif
> >  
> >  /* Definitions for ipx.h */
> > +#if !defined(__UAPI_DEF_SOCKADDR_IPX)
> >  #define __UAPI_DEF_SOCKADDR_IPX			1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPX_ROUTE_DEFINITION)
> >  #define __UAPI_DEF_IPX_ROUTE_DEFINITION		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPX_INTERFACE_DEFINITION)
> >  #define __UAPI_DEF_IPX_INTERFACE_DEFINITION	1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPX_CONFIG_DATA)
> >  #define __UAPI_DEF_IPX_CONFIG_DATA		1
> > +#endif
> > +#if !defined(__UAPI_DEF_IPX_ROUTE_DEF)
> >  #define __UAPI_DEF_IPX_ROUTE_DEF		1
> > +#endif
> >  
> >  /* Definitions for xattr.h */
> > +#if !defined(__UAPI_DEF_XATTR)
> >  #define __UAPI_DEF_XATTR		1
> > +#endif
> >  
> >  #endif /* __GLIBC__ */
> >  
> > 

--