include/cancel.h

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Copyright (C) 2000-2011 Erik Andersen <andersen@uclibc.org>
   4  *
   5  * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
   6  */
   7
   8 #ifndef _CANCEL_H
   9 #define _CANCEL_H
  10
  11 /*
  12  * Usage of this header:
  13  * 1. define a static or hidden function __NC(NAME) - expands to __NAME_nocancel
  14  * 2. if it is hidden, add the prototype to the appropiate header where NAME has
  15  * it's prototype (guarded by _LIBC)
  16  * 3. add a CANCELLABLE_SYSCALL(...) line at the end, this will create the function
  17  * NAME (as weak) with enabled cancellation for NPTL (and later for new LT), for
  18  * LT_OLD it will also create a strong_alias to __libc_NAME to be used in libpthread
  19  * 4. if you need libc_hidden_(weak|def) line, use instead lt_libc_hidden, this will
  20  * take care of the correct type, weak or strong depending on the THREADS type
  21  * 5. If the implementation can't be done using CANCELLABLE_SYSCALL (like for fcntl)
  22  * you need to manually add lt_strong_alias() line too, to optionally create the
  23  * __libc_NAME alias
  24  * 6. if functions are needed to implement __NC(NAME), that themselves are cancellable,
  25  * decide how the cancellation should be solved, two variants are possible:
  26  *  a. use the other function as __NC(FUNC), this way you access the non-cancellable
  27  *  variant and provide by CANCELLABLE_SYSCALL(...) the dedicated cancellation for NAME.
  28  *  be aware, that for this case __NC(FUNC) has to be hidden (not static)
  29  *  b. use the other function with it's name (FUNC) and add LIBC_CANCEL_HANDLED(); at
  30  *  the end of file with a comment telling us which function took care of the cancellation
  31  * Note: LIBC_CANCEL_HANDLED() is noop on uClibc, glibc uses it only for tests, we use
  32  * it only for "documentation".
  33  *
  34  * For now the use of this file is limited to libc, will expand later to support libpthread
  35  * and librt as well.
  36  */
  37
  38 #include <features.h>
  39
  40 #ifndef NOT_IN_libc
  41
  42 #define __NC(name) _NC(name)
  43 #define _NC(name) __##name##_nocancel
  44
  45 #define __NC_OLD(name) _NC_OLD(name)
  46 #define _NC_OLD(name) __libc_##name
  47
  48 #define __NC_PROTO(name) extern __typeof(name) __NC(name) attribute_hidden;
  49 #define __NC_OLD_PROTO(name) extern __typeof(name) __NC_OLD(name);
  50
  51 #if defined __UCLIBC_HAS_THREADS__ && !defined __LINUXTHREADS_OLD__
  52 # define __NEW_THREADS 1
  53 #else
  54 # define SINGLE_THREAD_P 1
  55 #endif
  56
  57 #ifdef __NEW_THREADS
  58 # include <sysdep-cancel.h>
  59
  60 # define CANCELLABLE_SYSCALL(res_type, name, param_list, params)        \
  61 res_type weak_function name param_list                                  \
  62 {                                                                       \
  63         if (SINGLE_THREAD_P)                                            \
  64                 return __NC(name) params;                               \
  65         int oldtype = LIBC_CANCEL_ASYNC();                              \
  66         res_type result = __NC(name) params;                            \
  67         LIBC_CANCEL_RESET(oldtype);                                     \
  68         return result;                                                  \
  69 }
  70
  71 # define lt_strong_alias(name)
  72 # define lt_libc_hidden(name) libc_hidden_def(name)
  73
  74 #elif defined __LINUXTHREADS_OLD__
  75
  76 # define CANCELLABLE_SYSCALL(res_type, name, param_list, params)        \
  77 weak_alias(__NC(name),name)                                             \
  78 lt_strong_alias(name)
  79
  80 # define lt_strong_alias(name)                                          \
  81 __NC_OLD_PROTO(name)                                                    \
  82 strong_alias(name,__NC_OLD(name))
  83 # define lt_libc_hidden(name) libc_hidden_weak(name)
  84
  85 #else
  86
  87 # define CANCELLABLE_SYSCALL(res_type, name, param_list, params)        \
  88 strong_alias(__NC(name),name)
  89
  90 # define lt_strong_alias(name)
  91 # define lt_libc_hidden(name) libc_hidden_def(name)
  92
  93 #endif
  94
  95 /* disable it, useless, glibc uses it only for tests */
  96 # undef LIBC_CANCEL_HANDLED
  97 # define LIBC_CANCEL_HANDLED()
  98
  99 #endif /* NOT_IN_libc */
 100
 101 #endif