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 #include "usterr_signal_safe.h"
  15
  16 #define SHM_MAGIC       0x54335433
  17 #define SHM_MAJOR       0
  18 #define SHM_MINOR       1
  19
  20 /*
  21  * Defining a max shm offset, for debugging purposes.
  22  */
  23 #if (CAA_BITS_PER_LONG == 32)
  24 /* Define the maximum shared memory size to 128MB on 32-bit machines */
  25 #define MAX_SHM_SIZE    134217728
  26 #else
  27 /* Define the maximum shared memory size to 8GB on 64-bit machines */
  28 #define MAX_SHM_SIZE    8589934592
  29 #endif
  30
  31 #define DECLARE_SHMP(type, name)        type *****name
  32
  33 struct shm_header {
  34         uint32_t magic;
  35         uint8_t major;
  36         uint8_t minor;
  37         uint8_t bits_per_long;
  38         size_t shm_size, shm_allocated;
  39
  40         DECLARE_SHMP(struct channel, chan);
  41 };
  42
  43 struct shm_handle {
  44         struct shm_header *header;      /* beginning of mapping */
  45         int shmfd;                      /* process-local file descriptor */
  46 };
  47
  48 #define shmp(shm_offset)                \
  49         ((__typeof__(****(shm_offset))) (((char *) &(shm_offset)) + (ptrdiff_t) (shm_offset)))
  50
  51 #define _shmp_abs(a)    ((a < 0) ? -(a) : (a))
  52
  53 static inline
  54 void _set_shmp(ptrdiff_t *shm_offset, void *ptr)
  55 {
  56         *shm_offset = (((char *) ptr) - ((char *) shm_offset));
  57         assert(_shmp_abs(*shm_offset) < MAX_SHM_SIZE);
  58 }
  59
  60 #define set_shmp(shm_offset, ptr)       \
  61         _set_shmp((ptrdiff_t *) ****(shm_offset), ptr)
  62
  63 /* Shared memory is already zeroed by shmget */
  64 /* *NOT* multithread-safe (should be protected by mutex) */
  65 static inline
  66 void *zalloc_shm(struct shm_header *shm_header, size_t len)
  67 {
  68         void *ret;
  69
  70         if (shm_header->shm_size - shm_header->shm_allocated < len)
  71                 return NULL;
  72         ret = (char *) shm_header + shm_header->shm_allocated;
  73         shm_header->shm_allocated += len;
  74         return ret;
  75 }
  76
  77 static inline
  78 void align_shm(struct shm_header *shm_header, size_t align)
  79 {
  80         size_t offset_len = offset_align(shm_header->shm_allocated, align);
  81         shm_header->shm_allocated += offset_len;
  82 }
  83
  84 #endif /* _LIBRINGBUFFER_SHM_H */