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          * Ignore the shm_unlink errors, because we handle leaks that
  71          * could occur by applications crashing between shm_open and
  72          * shm_unlink by unlinking the shm before every open. Therefore,
  73          * we can only leak one single shm (and only if the application
  74          * crashes between shm_open and the following shm_unlink).
  75          */
  76         do {
  77                 ret = shm_unlink("ust-shm-tmp");
  78                 if (ret < 0 && errno != ENOENT) {
  79                         PERROR("shm_unlink");
  80                         goto error_shm_unlink;
  81                 }
  82                 shmfd = shm_open("ust-shm-tmp",
  83                                  O_CREAT | O_EXCL | O_RDWR, 0700);
  84         } while (shmfd < 0 && errno == EEXIST);
  85         if (shmfd < 0) {
  86                 PERROR("shm_open");
  87                 goto error_shm_open;
  88         }
  89         ret = shm_unlink("ust-shm-tmp");
  90         if (ret < 0 && errno != ENOENT) {
  91                 PERROR("shm_unlink");
  92                 goto error_shm_release;
  93         }
  94         ret = ftruncate(shmfd, memory_map_size);
  95         if (ret) {
  96                 PERROR("ftruncate");
  97                 goto error_ftruncate;
  98         }
  99         obj->shm_fd = shmfd;
 100
 101         /* memory_map: mmap */
 102         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
 103                           MAP_SHARED, shmfd, 0);
 104         if (memory_map == MAP_FAILED) {
 105                 PERROR("mmap");
 106                 goto error_mmap;
 107         }
 108         obj->memory_map = memory_map;
 109         obj->memory_map_size = memory_map_size;
 110         obj->allocated_len = 0;
 111         obj->index = table->allocated_len++;
 112
 113         return obj;
 114
 115 error_mmap:
 116 error_ftruncate:
 117 error_shm_release:
 118         ret = close(shmfd);
 119         if (ret) {
 120                 PERROR("close");
 121                 assert(0);
 122         }
 123 error_shm_unlink:
 124 error_shm_open:
 125 error_fcntl:
 126         for (i = 0; i < 2; i++) {
 127                 ret = close(waitfd[i]);
 128                 if (ret) {
 129                         PERROR("close");
 130                         assert(0);
 131                 }
 132         }
 133 error_pipe:
 134         return NULL;
 135
 136 }
 137
 138 static
 139 void shmp_object_destroy(struct shm_object *obj)
 140 {
 141         int ret, i;
 142
 143         ret = munmap(obj->memory_map, obj->memory_map_size);
 144         if (ret) {
 145                 PERROR("umnmap");
 146                 assert(0);
 147         }
 148         ret = close(obj->shm_fd);
 149         if (ret) {
 150                 PERROR("close");
 151                 assert(0);
 152         }
 153         for (i = 0; i < 2; i++) {
 154                 ret = close(obj->wait_fd[i]);
 155                 if (ret) {
 156                         PERROR("close");
 157                         assert(0);
 158                 }
 159         }
 160 }
 161
 162 void shm_object_table_destroy(struct shm_object_table *table)
 163 {
 164         int i;
 165
 166         for (i = 0; i < table->allocated_len; i++)
 167                 shmp_object_destroy(&table->objects[i]);
 168         free(table);
 169 }
 170
 171 /*
 172  * zalloc_shm - allocate memory within a shm object.
 173  *
 174  * Shared memory is already zeroed by shmget.
 175  * *NOT* multithread-safe (should be protected by mutex).
 176  * Returns a -1, -1 tuple on error.
 177  */
 178 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len)
 179 {
 180         struct shm_ref ref;
 181         struct shm_ref shm_ref_error = { -1, -1 };
 182
 183         if (obj->memory_map_size - obj->allocated_len < len)
 184                 return shm_ref_error;
 185         ref.index = obj->index;
 186         ref.offset =  obj->allocated_len;
 187         obj->allocated_len += len;
 188         return ref;
 189 }
 190
 191 void align_shm(struct shm_object *obj, size_t align)
 192 {
 193         size_t offset_len = offset_align(obj->allocated_len, align);
 194         obj->allocated_len += offset_len;
 195 }