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 <lttng/align.h>
  20 #include <helper.h>
  21 #include <limits.h>
  22
  23 struct shm_object_table *shm_object_table_create(size_t max_nb_obj)
  24 {
  25         struct shm_object_table *table;
  26
  27         table = zmalloc(sizeof(struct shm_object_table) +
  28                         max_nb_obj * sizeof(table->objects[0]));
  29         table->size = max_nb_obj;
  30         return table;
  31 }
  32
  33 struct shm_object *shm_object_table_append(struct shm_object_table *table,
  34                                            size_t memory_map_size)
  35 {
  36         int shmfd, waitfd[2], ret, i, sigblocked = 0;
  37         struct shm_object *obj;
  38         char *memory_map;
  39         char tmp_name[NAME_MAX] = "ust-shm-tmp-XXXXXX";
  40         sigset_t all_sigs, orig_sigs;
  41
  42         if (table->allocated_len >= table->size)
  43                 return NULL;
  44         obj = &table->objects[table->allocated_len];
  45
  46         /* wait_fd: create pipe */
  47         ret = pipe(waitfd);
  48         if (ret < 0) {
  49                 PERROR("pipe");
  50                 goto error_pipe;
  51         }
  52         for (i = 0; i < 2; i++) {
  53                 ret = fcntl(waitfd[i], F_SETFD, FD_CLOEXEC);
  54                 if (ret < 0) {
  55                         PERROR("fcntl");
  56                         goto error_fcntl;
  57                 }
  58         }
  59         /* The write end of the pipe needs to be non-blocking */
  60         ret = fcntl(waitfd[1], F_SETFL, O_NONBLOCK);
  61         if (ret < 0) {
  62                 PERROR("fcntl");
  63                 goto error_fcntl;
  64         }
  65         memcpy(obj->wait_fd, waitfd, sizeof(waitfd));
  66
  67         /* shm_fd: create shm */
  68
  69         /*
  70          * Theoretically, we could leak a shm if the application crashes
  71          * between open and unlink. Disable signals on this thread for
  72          * increased safety against this scenario.
  73          */
  74         sigfillset(&all_sigs);
  75         ret = pthread_sigmask(SIG_BLOCK, &all_sigs, &orig_sigs);
  76         if (ret == -1) {
  77                 PERROR("pthread_sigmask");
  78                 goto error_pthread_sigmask;
  79         }
  80         sigblocked = 1;
  81
  82         /*
  83          * Allocate shm, and immediately unlink its shm oject, keeping
  84          * only the file descriptor as a reference to the object. If it
  85          * already exists (caused by short race window during which the
  86          * global object exists in a concurrent shm_open), simply retry.
  87          * We specifically do _not_ use the / at the beginning of the
  88          * pathname so that some OS implementations can keep it local to
  89          * the process (POSIX leaves this implementation-defined).
  90          */
  91         do {
  92                 /*
  93                  * Using mktemp filename with O_CREAT | O_EXCL open
  94                  * flags.
  95                  */
  96                 mktemp(tmp_name);
  97                 if (tmp_name[0] == '\0') {
  98                         PERROR("mktemp");
  99                         goto error_shm_open;
 100                 }
 101                 shmfd = shm_open(tmp_name,
 102                                  O_CREAT | O_EXCL | O_RDWR, 0700);
 103         } while (shmfd < 0 && (errno == EEXIST || errno == EACCES));
 104         if (shmfd < 0) {
 105                 PERROR("shm_open");
 106                 goto error_shm_open;
 107         }
 108         ret = shm_unlink(tmp_name);
 109         if (ret < 0 && errno != ENOENT) {
 110                 PERROR("shm_unlink");
 111                 goto error_shm_release;
 112         }
 113         sigblocked = 0;
 114         ret = pthread_sigmask(SIG_SETMASK, &orig_sigs, NULL);
 115         if (ret == -1) {
 116                 PERROR("pthread_sigmask");
 117                 goto error_sigmask_release;
 118         }
 119         ret = ftruncate(shmfd, memory_map_size);
 120         if (ret) {
 121                 PERROR("ftruncate");
 122                 goto error_ftruncate;
 123         }
 124         obj->shm_fd = shmfd;
 125
 126         /* memory_map: mmap */
 127         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
 128                           MAP_SHARED, shmfd, 0);
 129         if (memory_map == MAP_FAILED) {
 130                 PERROR("mmap");
 131                 goto error_mmap;
 132         }
 133         obj->memory_map = memory_map;
 134         obj->memory_map_size = memory_map_size;
 135         obj->allocated_len = 0;
 136         obj->index = table->allocated_len++;
 137
 138         return obj;
 139
 140 error_mmap:
 141 error_ftruncate:
 142 error_shm_release:
 143 error_sigmask_release:
 144         ret = close(shmfd);
 145         if (ret) {
 146                 PERROR("close");
 147                 assert(0);
 148         }
 149 error_shm_open:
 150         if (sigblocked) {
 151                 ret = pthread_sigmask(SIG_SETMASK, &orig_sigs, NULL);
 152                 if (ret == -1) {
 153                         PERROR("pthread_sigmask");
 154                 }
 155         }
 156 error_pthread_sigmask:
 157 error_fcntl:
 158         for (i = 0; i < 2; i++) {
 159                 ret = close(waitfd[i]);
 160                 if (ret) {
 161                         PERROR("close");
 162                         assert(0);
 163                 }
 164         }
 165 error_pipe:
 166         return NULL;
 167
 168 }
 169
 170 struct shm_object *shm_object_table_append_shadow(struct shm_object_table *table,
 171                         int shm_fd, int wait_fd, size_t memory_map_size)
 172 {
 173         struct shm_object *obj;
 174         char *memory_map;
 175
 176         if (table->allocated_len >= table->size)
 177                 return NULL;
 178         obj = &table->objects[table->allocated_len];
 179
 180         /* wait_fd: set read end of the pipe. */
 181         obj->wait_fd[0] = wait_fd;
 182         obj->wait_fd[1] = -1;   /* write end is unset. */
 183         obj->shm_fd = shm_fd;
 184
 185         /* memory_map: mmap */
 186         memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
 187                           MAP_SHARED, shm_fd, 0);
 188         if (memory_map == MAP_FAILED) {
 189                 PERROR("mmap");
 190                 goto error_mmap;
 191         }
 192         obj->memory_map = memory_map;
 193         obj->memory_map_size = memory_map_size;
 194         obj->allocated_len = memory_map_size;
 195         obj->index = table->allocated_len++;
 196
 197         return obj;
 198
 199 error_mmap:
 200         return NULL;
 201 }
 202
 203 static
 204 void shmp_object_destroy(struct shm_object *obj)
 205 {
 206         int ret, i;
 207
 208         if (!obj->is_shadow) {
 209                 ret = munmap(obj->memory_map, obj->memory_map_size);
 210                 if (ret) {
 211                         PERROR("umnmap");
 212                         assert(0);
 213                 }
 214         }
 215         if (obj->shm_fd >= 0) {
 216                 ret = close(obj->shm_fd);
 217                 if (ret) {
 218                         PERROR("close");
 219                         assert(0);
 220                 }
 221         }
 222         for (i = 0; i < 2; i++) {
 223                 if (obj->wait_fd[i] < 0)
 224                         continue;
 225                 ret = close(obj->wait_fd[i]);
 226                 if (ret) {
 227                         PERROR("close");
 228                         assert(0);
 229                 }
 230         }
 231 }
 232
 233 void shm_object_table_destroy(struct shm_object_table *table)
 234 {
 235         int i;
 236
 237         for (i = 0; i < table->allocated_len; i++)
 238                 shmp_object_destroy(&table->objects[i]);
 239         free(table);
 240 }
 241
 242 /*
 243  * zalloc_shm - allocate memory within a shm object.
 244  *
 245  * Shared memory is already zeroed by shmget.
 246  * *NOT* multithread-safe (should be protected by mutex).
 247  * Returns a -1, -1 tuple on error.
 248  */
 249 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len)
 250 {
 251         struct shm_ref ref;
 252         struct shm_ref shm_ref_error = { -1, -1 };
 253
 254         if (obj->memory_map_size - obj->allocated_len < len)
 255                 return shm_ref_error;
 256         ref.index = obj->index;
 257         ref.offset =  obj->allocated_len;
 258         obj->allocated_len += len;
 259         return ref;
 260 }
 261
 262 void align_shm(struct shm_object *obj, size_t align)
 263 {
 264         size_t offset_len = offset_align(obj->allocated_len, align);
 265         obj->allocated_len += offset_len;
 266 }