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 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, write to the
  18  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19  * Boston, MA 02111-1307, USA.
  20  */
  21
  22 #include "config.h"
  23
  24 #include <errno.h>
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <fcntl.h>
  28 #ifdef HAVE_UNISTD_H
  29 #include <unistd.h>
  30 #endif
  31 #ifdef HAVE_MMAP
  32 #include <sys/mman.h>
  33 #endif
  34
  35 #include "glibconfig.h"
  36
  37 #ifdef G_OS_WIN32
  38 #include <windows.h>
  39 #include <io.h>
  40
  41 #define fstat(a,b) _fstati64(a,b)
  42 #define stat _stati64
  43
  44 #endif
  45
  46 #include "gconvert.h"
  47 #include "gerror.h"
  48 #include "gfileutils.h"
  49 #include "gmappedfile.h"
  50 #include "gmem.h"
  51 #include "gmessages.h"
  52 #include "gstdio.h"
  53 #include "gstrfuncs.h"
  54 #include "gatomic.h"
  55 #include "gbuffer.h"
  56
  57 #include "glibintl.h"
  58
  59
  60 #ifndef _O_BINARY
  61 #define _O_BINARY 0
  62 #endif
  63
  64 #ifndef MAP_FAILED
  65 #define MAP_FAILED ((void *) -1)
  66 #endif
  67
  68 struct _GMappedFile
  69 {
  70   gchar *contents;
  71   gsize  length;
  72   gpointer free_func;
  73   int    ref_count;
  74 #ifdef G_OS_WIN32
  75   HANDLE mapping;
  76 #endif
  77 };
  78
  79 /* Make sure the layout of GMappedFile is the same as GBuffer's */
  80 G_STATIC_ASSERT (G_STRUCT_OFFSET (GMappedFile, contents) ==
  81                  G_STRUCT_OFFSET (GBuffer, data));
  82 G_STATIC_ASSERT (G_STRUCT_OFFSET (GMappedFile, length) ==
  83                  G_STRUCT_OFFSET (GBuffer, size));
  84 G_STATIC_ASSERT (G_STRUCT_OFFSET (GMappedFile, ref_count) ==
  85                  G_STRUCT_OFFSET (GBuffer, ref_count));
  86 G_STATIC_ASSERT (G_STRUCT_OFFSET (GMappedFile, free_func) ==
  87                  G_STRUCT_OFFSET (GBuffer, free_func));
  88
  89 static void
  90 g_mapped_file_destroy (GMappedFile *file)
  91 {
  92   if (file->length)
  93     {
  94 #ifdef HAVE_MMAP
  95       munmap (file->contents, file->length);
  96 #endif
  97 #ifdef G_OS_WIN32
  98       UnmapViewOfFile (file->contents);
  99       CloseHandle (file->mapping);
 100 #endif
 101     }
 102
 103   g_slice_free (GMappedFile, file);
 104 }
 105
 106 /**
 107  * g_mapped_file_new:
 108  * @filename: The path of the file to load, in the GLib filename encoding
 109  * @writable: whether the mapping should be writable
 110  * @error: return location for a #GError, or %NULL
 111  *
 112  * Maps a file into memory. On UNIX, this is using the mmap() function.
 113  *
 114  * If @writable is %TRUE, the mapped buffer may be modified, otherwise
 115  * it is an error to modify the mapped buffer. Modifications to the buffer
 116  * are not visible to other processes mapping the same file, and are not
 117  * written back to the file.
 118  *
 119  * Note that modifications of the underlying file might affect the contents
 120  * of the #GMappedFile. Therefore, mapping should only be used if the file
 121  * will not be modified, or if all modifications of the file are done
 122  * atomically (e.g. using g_file_set_contents()).
 123  *
 124  * Return value: a newly allocated #GMappedFile which must be unref'd
 125  *    with g_mapped_file_unref(), or %NULL if the mapping failed.
 126  *
 127  * Since: 2.8
 128  */
 129 GMappedFile *
 130 g_mapped_file_new (const gchar  *filename,
 131                    gboolean      writable,
 132                    GError      **error)
 133 {
 134   GMappedFile *file;
 135   int fd;
 136   struct stat st;
 137
 138   g_return_val_if_fail (filename != NULL, NULL);
 139   g_return_val_if_fail (!error || *error == NULL, NULL);
 140
 141   fd = g_open (filename, (writable ? O_RDWR : O_RDONLY) | _O_BINARY, 0);
 142   if (fd == -1)
 143     {
 144       int save_errno = errno;
 145       gchar *display_filename = g_filename_display_name (filename);
 146
 147       g_set_error (error,
 148                    G_FILE_ERROR,
 149                    g_file_error_from_errno (save_errno),
 150                    _("Failed to open file '%s': open() failed: %s"),
 151                    display_filename,
 152                    g_strerror (save_errno));
 153       g_free (display_filename);
 154       return NULL;
 155     }
 156
 157   file = g_slice_new0 (GMappedFile);
 158   file->ref_count = 1;
 159   file->free_func = g_mapped_file_destroy;
 160
 161   if (fstat (fd, &st) == -1)
 162     {
 163       int save_errno = errno;
 164       gchar *display_filename = g_filename_display_name (filename);
 165
 166       g_set_error (error,
 167                    G_FILE_ERROR,
 168                    g_file_error_from_errno (save_errno),
 169                    _("Failed to get attributes of file '%s': fstat() failed: %s"),
 170                    display_filename,
 171                    g_strerror (save_errno));
 172       g_free (display_filename);
 173       goto out;
 174     }
 175
 176   if (st.st_size == 0)
 177     {
 178       file->length = 0;
 179       file->contents = NULL;
 180       close (fd);
 181       return file;
 182     }
 183
 184   file->contents = MAP_FAILED;
 185
 186 #ifdef HAVE_MMAP
 187   if (st.st_size > G_MAXSIZE)
 188     {
 189       errno = EINVAL;
 190     }
 191   else
 192     {
 193       file->length = (gsize) st.st_size;
 194       file->contents = (gchar *) mmap (NULL,  file->length,
 195                                        writable ? PROT_READ|PROT_WRITE : PROT_READ,
 196                                        MAP_PRIVATE, fd, 0);
 197     }
 198 #endif
 199 #ifdef G_OS_WIN32
 200   file->length = st.st_size;
 201   file->mapping = CreateFileMapping ((HANDLE) _get_osfhandle (fd), NULL,
 202                                      writable ? PAGE_WRITECOPY : PAGE_READONLY,
 203                                      0, 0,
 204                                      NULL);
 205   if (file->mapping != NULL)
 206     {
 207       file->contents = MapViewOfFile (file->mapping,
 208                                       writable ? FILE_MAP_COPY : FILE_MAP_READ,
 209                                       0, 0,
 210                                       0);
 211       if (file->contents == NULL)
 212         {
 213           file->contents = MAP_FAILED;
 214           CloseHandle (file->mapping);
 215           file->mapping = NULL;
 216         }
 217     }
 218 #endif
 219
 220
 221   if (file->contents == MAP_FAILED)
 222     {
 223       int save_errno = errno;
 224       gchar *display_filename = g_filename_display_name (filename);
 225
 226       g_set_error (error,
 227                    G_FILE_ERROR,
 228                    g_file_error_from_errno (save_errno),
 229                    _("Failed to map file '%s': mmap() failed: %s"),
 230                    display_filename,
 231                    g_strerror (save_errno));
 232       g_free (display_filename);
 233       goto out;
 234     }
 235
 236   close (fd);
 237   return file;
 238
 239  out:
 240   close (fd);
 241   g_slice_free (GMappedFile, file);
 242
 243   return NULL;
 244 }
 245
 246 /**
 247  * g_mapped_file_get_length:
 248  * @file: a #GMappedFile
 249  *
 250  * Returns the length of the contents of a #GMappedFile.
 251  *
 252  * Returns: the length of the contents of @file.
 253  *
 254  * Since: 2.8
 255  */
 256 gsize
 257 g_mapped_file_get_length (GMappedFile *file)
 258 {
 259   g_return_val_if_fail (file != NULL, 0);
 260
 261   return file->length;
 262 }
 263
 264 /**
 265  * g_mapped_file_get_contents:
 266  * @file: a #GMappedFile
 267  *
 268  * Returns the contents of a #GMappedFile.
 269  *
 270  * Note that the contents may not be zero-terminated,
 271  * even if the #GMappedFile is backed by a text file.
 272  *
 273  * If the file is empty then %NULL is returned.
 274  *
 275  * Returns: the contents of @file, or %NULL.
 276  *
 277  * Since: 2.8
 278  */
 279 gchar *
 280 g_mapped_file_get_contents (GMappedFile *file)
 281 {
 282   g_return_val_if_fail (file != NULL, NULL);
 283
 284   return file->contents;
 285 }
 286
 287 /**
 288  * g_mapped_file_free:
 289  * @file: a #GMappedFile
 290  *
 291  * This call existed before #GMappedFile had refcounting and is currently
 292  * exactly the same as g_mapped_file_unref().
 293  *
 294  * Since: 2.8
 295  * Deprecated:2.22: Use g_mapped_file_unref() instead.
 296  */
 297 void
 298 g_mapped_file_free (GMappedFile *file)
 299 {
 300   g_mapped_file_unref (file);
 301 }
 302
 303 /**
 304  * g_mapped_file_ref:
 305  * @file: a #GMappedFile
 306  *
 307  * Increments the reference count of @file by one.  It is safe to call
 308  * this function from any thread.
 309  *
 310  * Return value: the passed in #GMappedFile.
 311  *
 312  * Since: 2.22
 313  **/
 314 GMappedFile *
 315 g_mapped_file_ref (GMappedFile *file)
 316 {
 317   g_return_val_if_fail (file != NULL, NULL);
 318   g_return_val_if_fail (file->ref_count > 0, file);
 319
 320   g_atomic_int_inc (&file->ref_count);
 321
 322   return file;
 323 }
 324
 325 /**
 326  * g_mapped_file_unref:
 327  * @file: a #GMappedFile
 328  *
 329  * Decrements the reference count of @file by one.  If the reference count
 330  * drops to 0, unmaps the buffer of @file and frees it.
 331  *
 332  * It is safe to call this function from any thread.
 333  *
 334  * Since 2.22
 335  **/
 336 void
 337 g_mapped_file_unref (GMappedFile *file)
 338 {
 339   g_return_if_fail (file != NULL);
 340   g_return_if_fail (file->ref_count > 0);
 341
 342   if (g_atomic_int_dec_and_test (&file->ref_count))
 343     g_mapped_file_destroy (file);
 344 }