libringbuffer/shm.h

   1 #ifndef _LIBRINGBUFFER_SHM_H
   2 #define _LIBRINGBUFFER_SHM_H
   3
   4 /*
   5  * libringbuffer/shm.h
   6  *
   7  * Copyright 2011 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Dual LGPL v2.1/GPL v2 license.
  10  */
  11
  12 #include <stdint.h>
  13 #include "ust/core.h"
  14
  15 #define SHM_MAGIC       0x54335433
  16 #define SHM_MAJOR       0
  17 #define SHM_MINOR       1
  18
  19 /*
  20  * Defining a max shm offset, for debugging purposes.
  21  */
  22 #if (CAA_BITS_PER_LONG == 32)
  23 /* Define the maximum shared memory size to 128MB on 32-bit machines */
  24 #define MAX_SHM_SIZE    134217728
  25 #else
  26 /* Define the maximum shared memory size to 8GB on 64-bit machines */
  27 #define MAX_SHM_SIZE    8589934592
  28 #endif
  29
  30 #define DECLARE_SHMP(type, name)        type *****name
  31
  32 struct shm_header {
  33         uint32_t magic;
  34         uint8_t major;
  35         uint8_t minor;
  36         uint8_t bits_per_long;
  37         size_t shm_size, shm_allocated;
  38
  39         DECLARE_SHMP(struct channel, chan);
  40 };
  41
  42 #define shmp(shm_offset)                \
  43         ((__typeof__(****(shm_offset))) (((char *) &(shm_offset)) + (ptrdiff_t) (shm_offset)))
  44
  45 #define _shmp_abs(a)    ((a < 0) ? -(a) : (a))
  46
  47 static inline
  48 void _set_shmp(ptrdiff_t *shm_offset, void *ptr)
  49 {
  50         *shm_offset = (((char *) ptr) - ((char *) shm_offset));
  51         assert(_shmp_abs(*shm_offset) < MAX_SHM_SIZE);
  52 }
  53
  54 #define set_shmp(shm_offset, ptr)       \
  55         _set_shmp((ptrdiff_t *) ****(shm_offset), ptr)
  56
  57 /* Shared memory is already zeroed by shmget */
  58 /* *NOT* multithread-safe (should be protected by mutex) */
  59 static inline
  60 void *zalloc_shm(struct shm_header *shm_header, size_t len)
  61 {
  62         void *ret;
  63
  64         if (shm_header->shm_size - shm_header->shm_allocated < len)
  65                 return NULL;
  66         ret = (char *) shm_header + shm_header->shm_allocated;
  67         shm_header->shm_allocated += len;
  68         return ret;
  69 }
  70
  71 #endif /* _LIBRINGBUFFER_SHM_H */