glib/gmappedfile.c

   1 /* GLIB - Library of useful routines for C programming
   2  * gmappedfile.c: Simplified wrapper around the mmap() function.
   3  *
   4  * Copyright 2005 Matthias Clasen
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include "config.h"
  21
  22 #include <errno.h>
  23 #include <sys/types.h>
  24 #include <sys/stat.h>
  25 #include <fcntl.h>
  26 #ifdef HAVE_MMAP
  27 #include <sys/mman.h>
  28 #endif
  29
  30 #include "glibconfig.h"
  31
  32 #ifdef G_OS_UNIX
  33 #include <unistd.h>
  34 #endif
  35
  36 #ifdef G_OS_WIN32
  37 #include <windows.h>
  38 #include <io.h>
  39
  40 #undef fstat
  41 #define fstat(a,b) _fstati64(a,b)
  42 #undef stat
  43 #define stat _stati64
  44
  45 #ifndef S_ISREG
  46 #define S_ISREG(m) (((m) & _S_IFMT) == _S_IFREG)
  47 #endif
  48
  49 #endif
  50
  51 #include "gconvert.h"
  52 #include "gerror.h"
  53 #include "gfileutils.h"
  54 #include "gmappedfile.h"
  55 #include "gmem.h"
  56 #include "gmessages.h"
  57 #include "gstdio.h"
  58 #include "gstrfuncs.h"
  59 #include "gatomic.h"
  60
  61 #include "glibintl.h"
  62
  63
  64 #ifndef _O_BINARY
  65 #define _O_BINARY 0
  66 #endif
  67
  68 #ifndef MAP_FAILED
  69 #define MAP_FAILED ((void *) -1)
  70 #endif
  71
  72 /**
  73  * GMappedFile:
  74  *
  75  * The #GMappedFile represents a file mapping created with
  76  * g_mapped_file_new(). It has only private members and should
  77  * not be accessed directly.
  78  */
  79
  80 struct _GMappedFile
  81 {
  82   gchar *contents;
  83   gsize  length;
  84   gpointer free_func;
  85   int    ref_count;
  86 #ifdef G_OS_WIN32
  87   HANDLE mapping;
  88 #endif
  89 };
  90
  91 static void
  92 g_mapped_file_destroy (GMappedFile *file)
  93 {
  94   if (file->length)
  95     {
  96 #ifdef HAVE_MMAP
  97       munmap (file->contents, file->length);
  98 #endif
  99 #ifdef G_OS_WIN32
 100       UnmapViewOfFile (file->contents);
 101       CloseHandle (file->mapping);
 102 #endif
 103     }
 104
 105   g_slice_free (GMappedFile, file);
 106 }
 107
 108 static GMappedFile*
 109 mapped_file_new_from_fd (int           fd,
 110                          gboolean      writable,
 111                          const gchar  *filename,
 112                          GError      **error)
 113 {
 114   GMappedFile *file;
 115   struct stat st;
 116
 117   file = g_slice_new0 (GMappedFile);
 118   file->ref_count = 1;
 119   file->free_func = g_mapped_file_destroy;
 120
 121   if (fstat (fd, &st) == -1)
 122     {
 123       int save_errno = errno;
 124       gchar *display_filename = filename ? g_filename_display_name (filename) : NULL;
 125
 126       g_set_error (error,
 127                    G_FILE_ERROR,
 128                    g_file_error_from_errno (save_errno),
 129                    _("Failed to get attributes of file “%s%s%s%s”: fstat() failed: %s"),
 130                    display_filename ? display_filename : "fd",
 131                    display_filename ? "' " : "",
 132                    display_filename ? display_filename : "",
 133                    display_filename ? "'" : "",
 134                    g_strerror (save_errno));
 135       g_free (display_filename);
 136       goto out;
 137     }
 138
 139   /* mmap() on size 0 will fail with EINVAL, so we avoid calling mmap()
 140    * in that case -- but only if we have a regular file; we still want
 141    * attempts to mmap a character device to fail, for example.
 142    */
 143   if (st.st_size == 0 && S_ISREG (st.st_mode))
 144     {
 145       file->length = 0;
 146       file->contents = NULL;
 147       return file;
 148     }
 149
 150   file->contents = MAP_FAILED;
 151
 152 #ifdef HAVE_MMAP
 153   if (st.st_size > G_MAXSIZE)
 154     {
 155       errno = EINVAL;
 156     }
 157   else
 158     {
 159       file->length = (gsize) st.st_size;
 160       file->contents = (gchar *) mmap (NULL,  file->length,
 161                                        writable ? PROT_READ|PROT_WRITE : PROT_READ,
 162                                        MAP_PRIVATE, fd, 0);
 163     }
 164 #endif
 165 #ifdef G_OS_WIN32
 166   file->length = st.st_size;
 167   file->mapping = CreateFileMapping ((HANDLE) _get_osfhandle (fd), NULL,
 168                                      writable ? PAGE_WRITECOPY : PAGE_READONLY,
 169                                      0, 0,
 170                                      NULL);
 171   if (file->mapping != NULL)
 172     {
 173       file->contents = MapViewOfFile (file->mapping,
 174                                       writable ? FILE_MAP_COPY : FILE_MAP_READ,
 175                                       0, 0,
 176                                       0);
 177       if (file->contents == NULL)
 178         {
 179           file->contents = MAP_FAILED;
 180           CloseHandle (file->mapping);
 181           file->mapping = NULL;
 182         }
 183     }
 184 #endif
 185
 186
 187   if (file->contents == MAP_FAILED)
 188     {
 189       int save_errno = errno;
 190       gchar *display_filename = filename ? g_filename_display_name (filename) : NULL;
 191
 192       g_set_error (error,
 193                    G_FILE_ERROR,
 194                    g_file_error_from_errno (save_errno),
 195                    _("Failed to map %s%s%s%s: mmap() failed: %s"),
 196                    display_filename ? display_filename : "fd",
 197                    display_filename ? "' " : "",
 198                    display_filename ? display_filename : "",
 199                    display_filename ? "'" : "",
 200                    g_strerror (save_errno));
 201       g_free (display_filename);
 202       goto out;
 203     }
 204
 205   return file;
 206
 207  out:
 208   g_slice_free (GMappedFile, file);
 209
 210   return NULL;
 211 }
 212
 213 /**
 214  * g_mapped_file_new:
 215  * @filename: (type filename): The path of the file to load, in the GLib
 216  *     filename encoding
 217  * @writable: whether the mapping should be writable
 218  * @error: return location for a #GError, or %NULL
 219  *
 220  * Maps a file into memory. On UNIX, this is using the mmap() function.
 221  *
 222  * If @writable is %TRUE, the mapped buffer may be modified, otherwise
 223  * it is an error to modify the mapped buffer. Modifications to the buffer
 224  * are not visible to other processes mapping the same file, and are not
 225  * written back to the file.
 226  *
 227  * Note that modifications of the underlying file might affect the contents
 228  * of the #GMappedFile. Therefore, mapping should only be used if the file
 229  * will not be modified, or if all modifications of the file are done
 230  * atomically (e.g. using g_file_set_contents()).
 231  *
 232  * If @filename is the name of an empty, regular file, the function
 233  * will successfully return an empty #GMappedFile. In other cases of
 234  * size 0 (e.g. device files such as /dev/null), @error will be set
 235  * to the #GFileError value #G_FILE_ERROR_INVAL.
 236  *
 237  * Returns: a newly allocated #GMappedFile which must be unref'd
 238  *    with g_mapped_file_unref(), or %NULL if the mapping failed.
 239  *
 240  * Since: 2.8
 241  */
 242 GMappedFile *
 243 g_mapped_file_new (const gchar  *filename,
 244                    gboolean      writable,
 245                    GError      **error)
 246 {
 247   GMappedFile *file;
 248   int fd;
 249
 250   g_return_val_if_fail (filename != NULL, NULL);
 251   g_return_val_if_fail (!error || *error == NULL, NULL);
 252
 253   fd = g_open (filename, (writable ? O_RDWR : O_RDONLY) | _O_BINARY, 0);
 254   if (fd == -1)
 255     {
 256       int save_errno = errno;
 257       gchar *display_filename = g_filename_display_name (filename);
 258
 259       g_set_error (error,
 260                    G_FILE_ERROR,
 261                    g_file_error_from_errno (save_errno),
 262                    _("Failed to open file “%s”: open() failed: %s"),
 263                    display_filename,
 264                    g_strerror (save_errno));
 265       g_free (display_filename);
 266       return NULL;
 267     }
 268
 269   file = mapped_file_new_from_fd (fd, writable, filename, error);
 270
 271   close (fd);
 272
 273   return file;
 274 }
 275
 276
 277 /**
 278  * g_mapped_file_new_from_fd:
 279  * @fd: The file descriptor of the file to load
 280  * @writable: whether the mapping should be writable
 281  * @error: return location for a #GError, or %NULL
 282  *
 283  * Maps a file into memory. On UNIX, this is using the mmap() function.
 284  *
 285  * If @writable is %TRUE, the mapped buffer may be modified, otherwise
 286  * it is an error to modify the mapped buffer. Modifications to the buffer
 287  * are not visible to other processes mapping the same file, and are not
 288  * written back to the file.
 289  *
 290  * Note that modifications of the underlying file might affect the contents
 291  * of the #GMappedFile. Therefore, mapping should only be used if the file
 292  * will not be modified, or if all modifications of the file are done
 293  * atomically (e.g. using g_file_set_contents()).
 294  *
 295  * Returns: a newly allocated #GMappedFile which must be unref'd
 296  *    with g_mapped_file_unref(), or %NULL if the mapping failed.
 297  *
 298  * Since: 2.32
 299  */
 300 GMappedFile *
 301 g_mapped_file_new_from_fd (gint          fd,
 302                            gboolean      writable,
 303                            GError      **error)
 304 {
 305   return mapped_file_new_from_fd (fd, writable, NULL, error);
 306 }
 307
 308 /**
 309  * g_mapped_file_get_length:
 310  * @file: a #GMappedFile
 311  *
 312  * Returns the length of the contents of a #GMappedFile.
 313  *
 314  * Returns: the length of the contents of @file.
 315  *
 316  * Since: 2.8
 317  */
 318 gsize
 319 g_mapped_file_get_length (GMappedFile *file)
 320 {
 321   g_return_val_if_fail (file != NULL, 0);
 322
 323   return file->length;
 324 }
 325
 326 /**
 327  * g_mapped_file_get_contents:
 328  * @file: a #GMappedFile
 329  *
 330  * Returns the contents of a #GMappedFile.
 331  *
 332  * Note that the contents may not be zero-terminated,
 333  * even if the #GMappedFile is backed by a text file.
 334  *
 335  * If the file is empty then %NULL is returned.
 336  *
 337  * Returns: the contents of @file, or %NULL.
 338  *
 339  * Since: 2.8
 340  */
 341 gchar *
 342 g_mapped_file_get_contents (GMappedFile *file)
 343 {
 344   g_return_val_if_fail (file != NULL, NULL);
 345
 346   return file->contents;
 347 }
 348
 349 /**
 350  * g_mapped_file_free:
 351  * @file: a #GMappedFile
 352  *
 353  * This call existed before #GMappedFile had refcounting and is currently
 354  * exactly the same as g_mapped_file_unref().
 355  *
 356  * Since: 2.8
 357  * Deprecated:2.22: Use g_mapped_file_unref() instead.
 358  */
 359 void
 360 g_mapped_file_free (GMappedFile *file)
 361 {
 362   g_mapped_file_unref (file);
 363 }
 364
 365 /**
 366  * g_mapped_file_ref:
 367  * @file: a #GMappedFile
 368  *
 369  * Increments the reference count of @file by one.  It is safe to call
 370  * this function from any thread.
 371  *
 372  * Returns: the passed in #GMappedFile.
 373  *
 374  * Since: 2.22
 375  **/
 376 GMappedFile *
 377 g_mapped_file_ref (GMappedFile *file)
 378 {
 379   g_return_val_if_fail (file != NULL, NULL);
 380
 381   g_atomic_int_inc (&file->ref_count);
 382
 383   return file;
 384 }
 385
 386 /**
 387  * g_mapped_file_unref:
 388  * @file: a #GMappedFile
 389  *
 390  * Decrements the reference count of @file by one.  If the reference count
 391  * drops to 0, unmaps the buffer of @file and frees it.
 392  *
 393  * It is safe to call this function from any thread.
 394  *
 395  * Since 2.22
 396  **/
 397 void
 398 g_mapped_file_unref (GMappedFile *file)
 399 {
 400   g_return_if_fail (file != NULL);
 401
 402   if (g_atomic_int_dec_and_test (&file->ref_count))
 403     g_mapped_file_destroy (file);
 404 }
 405
 406 /**
 407  * g_mapped_file_get_bytes:
 408  * @file: a #GMappedFile
 409  *
 410  * Creates a new #GBytes which references the data mapped from @file.
 411  * The mapped contents of the file must not be modified after creating this
 412  * bytes object, because a #GBytes should be immutable.
 413  *
 414  * Returns: (transfer full): A newly allocated #GBytes referencing data
 415  *     from @file
 416  *
 417  * Since: 2.34
 418  **/
 419 GBytes *
 420 g_mapped_file_get_bytes (GMappedFile *file)
 421 {
 422   g_return_val_if_fail (file != NULL, NULL);
 423
 424   return g_bytes_new_with_free_func (file->contents,
 425                                      file->length,
 426                                      (GDestroyNotify) g_mapped_file_unref,
 427                                      g_mapped_file_ref (file));
 428 }