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