libringbuffer/shm.c

   1 /*
   2  * libringbuffer/shm.c
   3  *
   4  * Copyright 2011 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Dual LGPL v2.1/GPL v2 license.
   7  */
   8
   9 #include "shm.h"
  10 #include <unistd.h>
  11 #include <fcntl.h>
  12 #include <sys/mman.h>
  13 #include <sys/stat.h>   /* For mode constants */
  14 #include <fcntl.h>      /* For O_* constants */
  15 #include <assert.h>
  16 #include <ust/align.h>
  17
  18 struct shm_object_table *shm_object_table_create(size_t max_nb_obj)
  19 {
  20         struct shm_object_table *table;
  21
  22         table = zmalloc(sizeof(struct shm_object_table) +
  23                         max_nb_obj * sizeof(table->objects[0]));
  24         table->size = max_nb_obj;
  25         return table;
  26 }
  27
  28 struct shm_object *shm_object_table_append(struct shm_object_table *table,
  29                                            size_t memory_map_size)
  30 {
  31         int shmfd, waitfd[2], ret, i;
  32         struct shm_object *obj;
  33         char *memory_map;
  34
  35         if (table->allocated_len >= table->size)
  36                 return NULL;
  37         obj = &table->objects[table->allocated_len];
  38
  39         /* wait_fd: create pipe */
  40         ret = pipe(waitfd);
  41         if (ret < 0) {
  42                 PERROR("pipe");
  43                 goto error_pipe;
  44         }
  45         for (i = 0; i < 2; i++) {
  46                 ret = fcntl(waitfd[i], F_SETFD, FD_CLOEXEC);
  47                 if (ret < 0) {
  48                         PERROR("fcntl");
  49                         goto error_fcntl;
  50                 }
  51         }
  52         /* The write end of the pipe needs to be non-blocking */
  53         ret = fcntl(waitfd[1], F_SETFL, O_NONBLOCK);
  54         if (ret < 0) {
  55                 PERROR("fcntl");
  56                 goto error_fcntl;
  57         }
  58         memcpy(obj->wait_fd, waitfd, sizeof(waitfd));
  59
  60         /* shm_fd: create shm */
  61
  62         /*
  63          * Allocate shm, and immediately unlink its shm oject, keeping
  64          * only the file descriptor as a reference to the object. If it
  65          * already exists (caused by short race window during which the
  66          * global object exists in a concurrent shm_open), simply retry.
  67          * We specifically do _not_ use the / at the beginning of the
  68          * pathname so that some OS implementations can keep it local to
  69          * the process (POSIX leaves this implementation-defined).
  70          */
  71         do {
  72                 shmfd = shm_open("ust-shm-tmp",
  73                                  O_CREAT | O_EXCL | O_RDWR, 0700);
  74         } while (shmfd < 0 && errno == EEXIST);
  75         if (shmfd < 0) {
  76                 PERROR("shm_open");
  77                 goto error_shm_open;
  78         }
  79         ret = shm_unlink("ust-shm-tmp");
  80         if (ret) {
  81                 PERROR("shm_unlink");
  82                 goto error_unlink;
  83         }
  84         ret = ftruncate(shmfd, memory_map_size);
  85         if (ret) {
  86                 PERROR("ftruncate");
  87                 goto error_ftruncate;
  88         }
  89         obj->shm_fd = shmfd;
  90
  91         /* memory_map: mmap */
  92         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
  93                           MAP_SHARED, shmfd, 0);
  94         if (memory_map == MAP_FAILED) {
  95                 PERROR("mmap");
  96                 goto error_mmap;
  97         }
  98         obj->memory_map = memory_map;
  99         obj->memory_map_size = memory_map_size;
 100         obj->allocated_len = 0;
 101
 102         table->allocated_len++;
 103         return obj;
 104
 105 error_mmap:
 106 error_ftruncate:
 107 error_unlink:
 108         ret = close(shmfd);
 109         if (ret) {
 110                 PERROR("close");
 111                 assert(0);
 112         }
 113 error_shm_open:
 114 error_fcntl:
 115         for (i = 0; i < 2; i++) {
 116                 ret = close(waitfd[i]);
 117                 if (ret) {
 118                         PERROR("close");
 119                         assert(0);
 120                 }
 121         }
 122 error_pipe:
 123         free(obj);
 124         return NULL;
 125
 126 }
 127
 128 static
 129 void shmp_object_destroy(struct shm_object *obj)
 130 {
 131         int ret, i;
 132
 133         ret = munmap(obj->memory_map, obj->memory_map_size);
 134         if (ret) {
 135                 PERROR("umnmap");
 136                 assert(0);
 137         }
 138         ret = close(obj->shm_fd);
 139         if (ret) {
 140                 PERROR("close");
 141                 assert(0);
 142         }
 143         for (i = 0; i < 2; i++) {
 144                 ret = close(obj->wait_fd[i]);
 145                 if (ret) {
 146                         PERROR("close");
 147                         assert(0);
 148                 }
 149         }
 150 }
 151
 152 void shm_object_table_destroy(struct shm_object_table *table)
 153 {
 154         int i;
 155
 156         for (i = 0; i < table->allocated_len; i++)
 157                 shmp_object_destroy(&table->objects[i]);
 158         free(table);
 159 }
 160
 161 /*
 162  * zalloc_shm - allocate memory within a shm object.
 163  *
 164  * Shared memory is already zeroed by shmget.
 165  * *NOT* multithread-safe (should be protected by mutex).
 166  * Returns a -1, -1 tuple on error.
 167  */
 168 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len)
 169 {
 170         struct shm_ref ref;
 171         struct shm_ref shm_ref_error = { -1, -1 };
 172
 173         if (obj->memory_map_size - obj->allocated_len < len)
 174                 return shm_ref_error;
 175         ref.index = obj->index;
 176         ref.offset =  obj->allocated_len;
 177         obj->allocated_len += len;
 178         return ref;
 179 }
 180
 181 void align_shm(struct shm_object *obj, size_t align)
 182 {
 183         size_t offset_len = offset_align(obj->allocated_len, align);
 184         obj->allocated_len += offset_len;
 185 }