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

[David Woodhouse <dwmw2@infradead.org>]

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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):

diff --git a/include/uapi/linux/libc-compat.h b/include/uapi/linux/libc-compat.h
index c316725..7673158 100644
--- a/include/uapi/linux/libc-compat.h
+++ b/include/uapi/linux/libc-compat.h
@@ -53,41 +53,18 @@
 
 /* Coordinate with glibc net/if.h header. */
 #if defined(_NET_IF_H) && defined(__USE_MISC)
-
 /* GLIBC headers included first so don't define anything
  * that would already be defined. */
-
 #define __UAPI_DEF_IF_IFCONF 0
 #define __UAPI_DEF_IF_IFMAP 0
 #define __UAPI_DEF_IF_IFNAMSIZ 0
 #define __UAPI_DEF_IF_IFREQ 0
 /* Everything up to IFF_DYNAMIC, matches net/if.h until glibc 2.23 */
 #define __UAPI_DEF_IF_NET_DEVICE_FLAGS 0
-/* For the future if glibc adds IFF_LOWER_UP, IFF_DORMANT and IFF_ECHO */
-#ifndef __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO
-#define __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO 1
-#endif /* __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO */
-
-#else /* _NET_IF_H */
-
-/* Linux headers included first, and we must define everything
- * we need. The expectation is that glibc will check the
- * __UAPI_DEF_* defines and adjust appropriately. */
-
-#define __UAPI_DEF_IF_IFCONF 1
-#define __UAPI_DEF_IF_IFMAP 1
-#define __UAPI_DEF_IF_IFNAMSIZ 1
-#define __UAPI_DEF_IF_IFREQ 1
-/* Everything up to IFF_DYNAMIC, matches net/if.h until glibc 2.23 */
-#define __UAPI_DEF_IF_NET_DEVICE_FLAGS 1
-/* For the future if glibc adds IFF_LOWER_UP, IFF_DORMANT and IFF_ECHO */
-#define __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO 1
-
 #endif /* _NET_IF_H */
 
 /* Coordinate with glibc netinet/in.h header. */
 #if defined(_NETINET_IN_H)
-
 /* GLIBC headers included first so don't define anything
  * that would already be defined. */
 #define __UAPI_DEF_IN_ADDR		0
@@ -104,8 +81,6 @@
  * additional in6_addr macros e.g. s6_addr16, and s6_addr32. */
 #if defined(__USE_MISC) || defined (__USE_GNU)
 #define __UAPI_DEF_IN6_ADDR_ALT		0
-#else
-#define __UAPI_DEF_IN6_ADDR_ALT		1
 #endif
 #define __UAPI_DEF_SOCKADDR_IN6		0
 #define __UAPI_DEF_IPV6_MREQ		0
@@ -113,62 +88,23 @@
 #define __UAPI_DEF_IPV6_OPTIONS		0
 #define __UAPI_DEF_IN6_PKTINFO		0
 #define __UAPI_DEF_IP6_MTUINFO		0
-
-#else
-
-/* Linux headers included first, and we must define everything
- * we need. The expectation is that glibc will check the
- * __UAPI_DEF_* defines and adjust appropriately. */
-#define __UAPI_DEF_IN_ADDR		1
-#define __UAPI_DEF_IN_IPPROTO		1
-#define __UAPI_DEF_IN_PKTINFO		1
-#define __UAPI_DEF_IP_MREQ		1
-#define __UAPI_DEF_SOCKADDR_IN		1
-#define __UAPI_DEF_IN_CLASS		1
-
-#define __UAPI_DEF_IN6_ADDR		1
-/* We unconditionally define the in6_addr macros and glibc must
- * coordinate. */
-#define __UAPI_DEF_IN6_ADDR_ALT		1
-#define __UAPI_DEF_SOCKADDR_IN6		1
-#define __UAPI_DEF_IPV6_MREQ		1
-#define __UAPI_DEF_IPPROTO_V6		1
-#define __UAPI_DEF_IPV6_OPTIONS		1
-#define __UAPI_DEF_IN6_PKTINFO		1
-#define __UAPI_DEF_IP6_MTUINFO		1
-
 #endif /* _NETINET_IN_H */
 
 /* Coordinate with glibc netipx/ipx.h header. */
 #if defined(__NETIPX_IPX_H)
-
 #define __UAPI_DEF_SOCKADDR_IPX			0
 #define __UAPI_DEF_IPX_ROUTE_DEFINITION		0
 #define __UAPI_DEF_IPX_INTERFACE_DEFINITION	0
 #define __UAPI_DEF_IPX_CONFIG_DATA		0
 #define __UAPI_DEF_IPX_ROUTE_DEF		0
-
-#else /* defined(__NETIPX_IPX_H) */
-
-#define __UAPI_DEF_SOCKADDR_IPX			1
-#define __UAPI_DEF_IPX_ROUTE_DEFINITION		1
-#define __UAPI_DEF_IPX_INTERFACE_DEFINITION	1
-#define __UAPI_DEF_IPX_CONFIG_DATA		1
-#define __UAPI_DEF_IPX_ROUTE_DEF		1
-
 #endif /* defined(__NETIPX_IPX_H) */
 
 /* Definitions for xattr.h */
 #if defined(_SYS_XATTR_H)
 #define __UAPI_DEF_XATTR		0
-#else
-#define __UAPI_DEF_XATTR		1
 #endif
 
-/* If we did not see any headers from any supported C libraries,
- * or we are being included in the kernel, then define everything
- * that we need. */
-#else /* !defined(__GLIBC__) */
+#endif /* __GLIBC__ */
 
 /* Definitions for if.h */
 #if !defined(__UAPI_DEF_IF_IFCONF)
@@ -260,6 +196,4 @@
 #define __UAPI_DEF_XATTR		1
 #endif
 
-#endif /* __GLIBC__ */
-
 #endif /* _UAPI_LIBC_COMPAT_H */






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