lib/ccan/tcon/tcon.h

   1 /* Placed into the public domain */
   2 #ifndef CCAN_TCON_H
   3 #define CCAN_TCON_H
   4 #include "config.h"
   5
   6 /**
   7  * TCON - declare a _tcon type containing canary variables.
   8  * @decls: the semi-colon separated list of type canaries.
   9  *
  10  * This declares a _tcon member for a structure.  It should be the
  11  * last element in your structure; with sufficient compiler support it
  12  * will not use any actual storage.  tcon_check() will compare
  13  * expressions with one of these "type canaries" to cause warnings if
  14  * the container is misused.
  15  *
  16  * A type of "void *" will allow tcon_check() to pass on any (pointer) type.
  17  *
  18  * Example:
  19  *      // Simply typesafe linked list.
  20  *      struct list_head {
  21  *              struct list_head *prev, *next;
  22  *      };
  23  *
  24  *      struct string_list {
  25  *              struct list_head raw;
  26  *              TCON(char *canary);
  27  *      };
  28  *
  29  *      // More complex: mapping from one type to another.
  30  *      struct map {
  31  *              void *contents;
  32  *      };
  33  *
  34  *      struct int_to_string_map {
  35  *              struct map raw;
  36  *              TCON(char *charp_canary; int int_canary);
  37  *      };
  38  */
  39 #if HAVE_FLEXIBLE_ARRAY_MEMBER
  40 #define TCON(decls) struct { decls; } _tcon[]
  41 #else
  42 #define TCON(decls) struct { decls; } _tcon[1]
  43 #endif
  44
  45 /**
  46  * tcon_check - typecheck a typed container
  47  * @x: the structure containing the TCON.
  48  * @canary: which canary to check against.
  49  * @expr: the expression whose type must match the TCON (not evaluated)
  50  *
  51  * This macro is used to check that the expression is the type
  52  * expected for this structure (note the "useless" sizeof() argument
  53  * which contains this comparison with the type canary).
  54  *
  55  * It evaluates to @x so you can chain it.
  56  *
  57  * Example:
  58  *      #define tlist_add(h, n, member) \
  59  *              list_add(&tcon_check((h), canary, (n))->raw, &(n)->member)
  60  */
  61 #define tcon_check(x, canary, expr)                             \
  62         (sizeof((x)->_tcon[0].canary == (expr)) ? (x) : (x))
  63
  64 /**
  65  * tcon_check_ptr - typecheck a typed container
  66  * @x: the structure containing the TCON.
  67  * @canary: which canary to check against.
  68  * @expr: the expression whose type must match &TCON (not evaluated)
  69  *
  70  * This macro is used to check that the expression is a pointer to the type
  71  * expected for this structure (note the "useless" sizeof() argument
  72  * which contains this comparison with the type canary), or NULL.
  73  *
  74  * It evaluates to @x so you can chain it.
  75  */
  76 #define tcon_check_ptr(x, canary, expr)                         \
  77         (sizeof(&(x)->_tcon[0].canary == (expr)) ? (x) : (x))
  78
  79
  80 /**
  81  * tcon_type - the type within a container (or void *)
  82  * @x: the structure containing the TCON.
  83  * @canary: which canary to check against.
  84  */
  85 #if HAVE_TYPEOF
  86 #define tcon_type(x, canary) __typeof__((x)->_tcon[0].canary)
  87 #else
  88 #define tcon_type(x, canary) void *
  89 #endif
  90
  91 /**
  92  * tcon_ptr_type - pointer to the type within a container (or void *)
  93  * @x: the structure containing the TCON.
  94  * @canary: which canary to check against.
  95  */
  96 #if HAVE_TYPEOF
  97 #define tcon_ptr_type(x, canary) __typeof__(&(x)->_tcon[0].canary)
  98 #else
  99 #define tcon_ptr_type(x, canary) void *
 100 #endif
 101
 102 /**
 103  * tcon_cast - cast to a canary type for this container (or void *)
 104  * @x: a structure containing the TCON.
 105  * @canary: which canary to cast to.
 106  * @expr: the value to cast
 107  *
 108  * This is used to cast to the correct type for this container.  If the
 109  * platform doesn't HAVE_TYPEOF, then it casts to void * (which will
 110  * cause a warning if the user doesn't expect a pointer type).
 111  */
 112 #define tcon_cast(x, canary, expr) ((tcon_type((x), canary))(expr))
 113 #define tcon_cast_ptr(x, canary, expr) ((tcon_ptr_type((x), canary))(expr))
 114
 115 #endif /* CCAN_TCON_H */