include/uapi/linux/libc-compat.h

   1 /*
   2  * Compatibility interface for userspace libc header coordination:
   3  *
   4  * Define compatibility macros that are used to control the inclusion or
   5  * exclusion of UAPI structures and definitions in coordination with another
   6  * userspace C library.
   7  *
   8  * This header is intended to solve the problem of UAPI definitions that
   9  * conflict with userspace definitions. If a UAPI header has such conflicting
  10  * definitions then the solution is as follows:
  11  *
  12  * * Synchronize the UAPI header and the libc headers so either one can be
  13  *   used and such that the ABI is preserved. If this is not possible then
  14  *   no simple compatibility interface exists (you need to write translating
  15  *   wrappers and rename things) and you can't use this interface.
  16  *
  17  * Then follow this process:
  18  *
  19  * (a) Include libc-compat.h in the UAPI header.
  20  *      e.g. #include <linux/libc-compat.h>
  21  *     This include must be as early as possible.
  22  *
  23  * (b) In libc-compat.h add enough code to detect that the comflicting
  24  *     userspace libc header has been included first.
  25  *
  26  * (c) If the userspace libc header has been included first define a set of
  27  *     guard macros of the form __UAPI_DEF_FOO and set their values to 1, else
  28  *     set their values to 0.
  29  *
  30  * (d) Back in the UAPI header with the conflicting definitions, guard the
  31  *     definitions with:
  32  *     #if __UAPI_DEF_FOO
  33  *       ...
  34  *     #endif
  35  *
  36  * This fixes the situation where the linux headers are included *after* the
  37  * libc headers. To fix the problem with the inclusion in the other order the
  38  * userspace libc headers must be fixed like this:
  39  *
  40  * * For all definitions that conflict with kernel definitions wrap those
  41  *   defines in the following:
  42  *   #if !__UAPI_DEF_FOO
  43  *     ...
  44  *   #endif
  45  *
  46  * This prevents the redefinition of a construct already defined by the kernel.
  47  */
  48 #ifndef _UAPI_LIBC_COMPAT_H
  49 #define _UAPI_LIBC_COMPAT_H
  50
  51 /* We have included glibc headers... */
  52 #if defined(__GLIBC__)
  53
  54 /* Coordinate with glibc netinet/in.h header. */
  55 #if defined(_NETINET_IN_H)
  56
  57 /* GLIBC headers included first so don't define anything
  58  * that would already be defined. */
  59 #define __UAPI_DEF_IN6_ADDR             0
  60 /* The exception is the in6_addr macros which must be defined
  61  * if the glibc code didn't define them. This guard matches
  62  * the guard in glibc/inet/netinet/in.h which defines the
  63  * additional in6_addr macros e.g. s6_addr16, and s6_addr32. */
  64 #if defined(__USE_MISC) || defined (__USE_GNU)
  65 #define __UAPI_DEF_IN6_ADDR_ALT         0
  66 #else
  67 #define __UAPI_DEF_IN6_ADDR_ALT         1
  68 #endif
  69 #define __UAPI_DEF_SOCKADDR_IN6         0
  70 #define __UAPI_DEF_IPV6_MREQ            0
  71 #define __UAPI_DEF_IPPROTO_V6           0
  72
  73 #else
  74
  75 /* Linux headers included first, and we must define everything
  76  * we need. The expectation is that glibc will check the
  77  * __UAPI_DEF_* defines and adjust appropriately. */
  78 #define __UAPI_DEF_IN6_ADDR             1
  79 /* We unconditionally define the in6_addr macros and glibc must
  80  * coordinate. */
  81 #define __UAPI_DEF_IN6_ADDR_ALT         1
  82 #define __UAPI_DEF_SOCKADDR_IN6         1
  83 #define __UAPI_DEF_IPV6_MREQ            1
  84 #define __UAPI_DEF_IPPROTO_V6           1
  85
  86 #endif /* _NETINET_IN_H */
  87
  88
  89 /* If we did not see any headers from any supported C libraries,
  90  * or we are being included in the kernel, then define everything
  91  * that we need. */
  92 #else /* !defined(__GLIBC__) */
  93
  94 /* Definitions for in6.h */
  95 #define __UAPI_DEF_IN6_ADDR             1
  96 #define __UAPI_DEF_IN6_ADDR_ALT         1
  97 #define __UAPI_DEF_SOCKADDR_IN6         1
  98 #define __UAPI_DEF_IPV6_MREQ            1
  99 #define __UAPI_DEF_IPPROTO_V6           1
 100
 101 #endif /* __GLIBC__ */
 102
 103 #endif /* _UAPI_LIBC_COMPAT_H */