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 <stdio.h>
  17 #include <signal.h>
  18 #include <dirent.h>
  19 #include <ust/align.h>
  20
  21 struct shm_object_table *shm_object_table_create(size_t max_nb_obj)
  22 {
  23         struct shm_object_table *table;
  24
  25         table = zmalloc(sizeof(struct shm_object_table) +
  26                         max_nb_obj * sizeof(table->objects[0]));
  27         table->size = max_nb_obj;
  28         return table;
  29 }
  30
  31 struct shm_object *shm_object_table_append(struct shm_object_table *table,
  32                                            size_t memory_map_size)
  33 {
  34         int shmfd, waitfd[2], ret, i, sigblocked = 0;
  35         struct shm_object *obj;
  36         char *memory_map;
  37         char tmp_name[NAME_MAX] = "ust-shm-tmp-XXXXXX";
  38         sigset_t all_sigs, orig_sigs;
  39
  40         if (table->allocated_len >= table->size)
  41                 return NULL;
  42         obj = &table->objects[table->allocated_len];
  43
  44         /* wait_fd: create pipe */
  45         ret = pipe(waitfd);
  46         if (ret < 0) {
  47                 PERROR("pipe");
  48                 goto error_pipe;
  49         }
  50         for (i = 0; i < 2; i++) {
  51                 ret = fcntl(waitfd[i], F_SETFD, FD_CLOEXEC);
  52                 if (ret < 0) {
  53                         PERROR("fcntl");
  54                         goto error_fcntl;
  55                 }
  56         }
  57         /* The write end of the pipe needs to be non-blocking */
  58         ret = fcntl(waitfd[1], F_SETFL, O_NONBLOCK);
  59         if (ret < 0) {
  60                 PERROR("fcntl");
  61                 goto error_fcntl;
  62         }
  63         memcpy(obj->wait_fd, waitfd, sizeof(waitfd));
  64
  65         /* shm_fd: create shm */
  66
  67         /*
  68          * Theoretically, we could leak a shm if the application crashes
  69          * between open and unlink. Disable signals on this thread for
  70          * increased safety against this scenario.
  71          */
  72         sigfillset(&all_sigs);
  73         ret = pthread_sigmask(SIG_BLOCK, &all_sigs, &orig_sigs);
  74         if (ret == -1) {
  75                 PERROR("pthread_sigmask");
  76                 goto error_pthread_sigmask;
  77         }
  78         sigblocked = 1;
  79
  80         /*
  81          * Allocate shm, and immediately unlink its shm oject, keeping
  82          * only the file descriptor as a reference to the object. If it
  83          * already exists (caused by short race window during which the
  84          * global object exists in a concurrent shm_open), simply retry.
  85          * We specifically do _not_ use the / at the beginning of the
  86          * pathname so that some OS implementations can keep it local to
  87          * the process (POSIX leaves this implementation-defined).
  88          */
  89         do {
  90                 /*
  91                  * Using mktemp filename with O_CREAT | O_EXCL open
  92                  * flags.
  93                  */
  94                 mktemp(tmp_name);
  95                 if (tmp_name[0] == '\0') {
  96                         PERROR("mktemp");
  97                         goto error_shm_open;
  98                 }
  99                 shmfd = shm_open(tmp_name,
 100                                  O_CREAT | O_EXCL | O_RDWR, 0700);
 101         } while (shmfd < 0 && (errno == EEXIST || errno == EACCES));
 102         if (shmfd < 0) {
 103                 PERROR("shm_open");
 104                 goto error_shm_open;
 105         }
 106         ret = shm_unlink(tmp_name);
 107         if (ret < 0 && errno != ENOENT) {
 108                 PERROR("shm_unlink");
 109                 goto error_shm_release;
 110         }
 111         sigblocked = 0;
 112         ret = pthread_sigmask(SIG_SETMASK, &orig_sigs, NULL);
 113         if (ret == -1) {
 114                 PERROR("pthread_sigmask");
 115                 goto error_sigmask_release;
 116         }
 117         ret = ftruncate(shmfd, memory_map_size);
 118         if (ret) {
 119                 PERROR("ftruncate");
 120                 goto error_ftruncate;
 121         }
 122         obj->shm_fd = shmfd;
 123
 124         /* memory_map: mmap */
 125         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
 126                           MAP_SHARED, shmfd, 0);
 127         if (memory_map == MAP_FAILED) {
 128                 PERROR("mmap");
 129                 goto error_mmap;
 130         }
 131         obj->memory_map = memory_map;
 132         obj->memory_map_size = memory_map_size;
 133         obj->allocated_len = 0;
 134         obj->index = table->allocated_len++;
 135
 136         return obj;
 137
 138 error_mmap:
 139 error_ftruncate:
 140 error_shm_release:
 141 error_sigmask_release:
 142         ret = close(shmfd);
 143         if (ret) {
 144                 PERROR("close");
 145                 assert(0);
 146         }
 147 error_shm_open:
 148         if (sigblocked) {
 149                 ret = pthread_sigmask(SIG_SETMASK, &orig_sigs, NULL);
 150                 if (ret == -1) {
 151                         PERROR("pthread_sigmask");
 152                 }
 153         }
 154 error_pthread_sigmask:
 155 error_fcntl:
 156         for (i = 0; i < 2; i++) {
 157                 ret = close(waitfd[i]);
 158                 if (ret) {
 159                         PERROR("close");
 160                         assert(0);
 161                 }
 162         }
 163 error_pipe:
 164         return NULL;
 165
 166 }
 167
 168 struct shm_object *shm_object_table_append_shadow(struct shm_object_table *table,
 169                         int shm_fd, int wait_fd, size_t memory_map_size)
 170 {
 171         struct shm_object *obj;
 172         char *memory_map;
 173
 174         if (table->allocated_len >= table->size)
 175                 return NULL;
 176         obj = &table->objects[table->allocated_len];
 177
 178         /* wait_fd: set read end of the pipe. */
 179         obj->wait_fd[0] = wait_fd;
 180         obj->wait_fd[1] = -1;   /* write end is unset. */
 181         obj->shm_fd = shm_fd;
 182
 183         /* memory_map: mmap */
 184         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
 185                           MAP_SHARED, shm_fd, 0);
 186         if (memory_map == MAP_FAILED) {
 187                 PERROR("mmap");
 188                 goto error_mmap;
 189         }
 190         obj->memory_map = memory_map;
 191         obj->memory_map_size = memory_map_size;
 192         obj->allocated_len = memory_map_size;
 193         obj->index = table->allocated_len++;
 194
 195         return obj;
 196
 197 error_mmap:
 198         return NULL;
 199 }
 200
 201 static
 202 void shmp_object_destroy(struct shm_object *obj)
 203 {
 204         int ret, i;
 205
 206         ret = munmap(obj->memory_map, obj->memory_map_size);
 207         if (ret) {
 208                 PERROR("umnmap");
 209                 assert(0);
 210         }
 211         ret = close(obj->shm_fd);
 212         if (ret) {
 213                 PERROR("close");
 214                 assert(0);
 215         }
 216         for (i = 0; i < 2; i++) {
 217                 if (obj->wait_fd[i] < 0)
 218                         continue;
 219                 ret = close(obj->wait_fd[i]);
 220                 if (ret) {
 221                         PERROR("close");
 222                         assert(0);
 223                 }
 224         }
 225 }
 226
 227 void shm_object_table_destroy(struct shm_object_table *table)
 228 {
 229         int i;
 230
 231         for (i = 0; i < table->allocated_len; i++)
 232                 shmp_object_destroy(&table->objects[i]);
 233         free(table);
 234 }
 235
 236 /*
 237  * zalloc_shm - allocate memory within a shm object.
 238  *
 239  * Shared memory is already zeroed by shmget.
 240  * *NOT* multithread-safe (should be protected by mutex).
 241  * Returns a -1, -1 tuple on error.
 242  */
 243 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len)
 244 {
 245         struct shm_ref ref;
 246         struct shm_ref shm_ref_error = { -1, -1 };
 247
 248         if (obj->memory_map_size - obj->allocated_len < len)
 249                 return shm_ref_error;
 250         ref.index = obj->index;
 251         ref.offset =  obj->allocated_len;
 252         obj->allocated_len += len;
 253         return ref;
 254 }
 255
 256 void align_shm(struct shm_object *obj, size_t align)
 257 {
 258         size_t offset_len = offset_align(obj->allocated_len, align);
 259         obj->allocated_len += offset_len;
 260 }