gio/gvolume.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2006-2007 Red Hat, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2.1 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General
  16  * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
  17  *
  18  * Author: Alexander Larsson <alexl@redhat.com>
  19  *         David Zeuthen <davidz@redhat.com>
  20  */
  21
  22 #include "config.h"
  23 #include "gmount.h"
  24 #include "gvolume.h"
  25 #include "gthemedicon.h"
  26 #include "gasyncresult.h"
  27 #include "gtask.h"
  28 #include "gioerror.h"
  29 #include "glibintl.h"
  30
  31
  32 /**
  33  * SECTION:gvolume
  34  * @short_description: Volume management
  35  * @include: gio/gio.h
  36  *
  37  * The #GVolume interface represents user-visible objects that can be
  38  * mounted. Note, when porting from GnomeVFS, #GVolume is the moral
  39  * equivalent of #GnomeVFSDrive.
  40  *
  41  * Mounting a #GVolume instance is an asynchronous operation. For more
  42  * information about asynchronous operations, see #GAsyncResult and
  43  * #GTask. To mount a #GVolume, first call g_volume_mount() with (at
  44  * least) the #GVolume instance, optionally a #GMountOperation object
  45  * and a #GAsyncReadyCallback.
  46  *
  47  * Typically, one will only want to pass %NULL for the
  48  * #GMountOperation if automounting all volumes when a desktop session
  49  * starts since it's not desirable to put up a lot of dialogs asking
  50  * for credentials.
  51  *
  52  * The callback will be fired when the operation has resolved (either
  53  * with success or failure), and a #GAsyncReady structure will be
  54  * passed to the callback.  That callback should then call
  55  * g_volume_mount_finish() with the #GVolume instance and the
  56  * #GAsyncReady data to see if the operation was completed
  57  * successfully.  If an @error is present when g_volume_mount_finish()
  58  * is called, then it will be filled with any error information.
  59  *
  60  * ## Volume Identifiers # {#volume-identifier}
  61  *
  62  * It is sometimes necessary to directly access the underlying
  63  * operating system object behind a volume (e.g. for passing a volume
  64  * to an application via the commandline). For this purpose, GIO
  65  * allows to obtain an 'identifier' for the volume. There can be
  66  * different kinds of identifiers, such as Hal UDIs, filesystem labels,
  67  * traditional Unix devices (e.g. `/dev/sda2`), UUIDs. GIO uses predefined
  68  * strings as names for the different kinds of identifiers:
  69  * #G_VOLUME_IDENTIFIER_KIND_HAL_UDI, #G_VOLUME_IDENTIFIER_KIND_LABEL, etc.
  70  * Use g_volume_get_identifier() to obtain an identifier for a volume.
  71  *
  72  *
  73  * Note that #G_VOLUME_IDENTIFIER_KIND_HAL_UDI will only be available
  74  * when the gvfs hal volume monitor is in use. Other volume monitors
  75  * will generally be able to provide the #G_VOLUME_IDENTIFIER_KIND_UNIX_DEVICE
  76  * identifier, which can be used to obtain a hal device by means of
  77  * libhal_manager_find_device_string_match().
  78  */
  79
  80 typedef GVolumeIface GVolumeInterface;
  81 G_DEFINE_INTERFACE(GVolume, g_volume, G_TYPE_OBJECT)
  82
  83 static void
  84 g_volume_default_init (GVolumeInterface *iface)
  85 {
  86   /**
  87    * GVolume::changed:
  88    *
  89    * Emitted when the volume has been changed.
  90    */
  91   g_signal_new (I_("changed"),
  92                 G_TYPE_VOLUME,
  93                 G_SIGNAL_RUN_LAST,
  94                 G_STRUCT_OFFSET (GVolumeIface, changed),
  95                 NULL, NULL,
  96                 g_cclosure_marshal_VOID__VOID,
  97                 G_TYPE_NONE, 0);
  98
  99   /**
 100    * GVolume::removed:
 101    *
 102    * This signal is emitted when the #GVolume have been removed. If
 103    * the recipient is holding references to the object they should
 104    * release them so the object can be finalized.
 105    */
 106   g_signal_new (I_("removed"),
 107                 G_TYPE_VOLUME,
 108                 G_SIGNAL_RUN_LAST,
 109                 G_STRUCT_OFFSET (GVolumeIface, removed),
 110                 NULL, NULL,
 111                 g_cclosure_marshal_VOID__VOID,
 112                 G_TYPE_NONE, 0);
 113 }
 114
 115 /**
 116  * g_volume_get_name:
 117  * @volume: a #GVolume
 118  *
 119  * Gets the name of @volume.
 120  *
 121  * Returns: the name for the given @volume. The returned string should
 122  *     be freed with g_free() when no longer needed.
 123  */
 124 char *
 125 g_volume_get_name (GVolume *volume)
 126 {
 127   GVolumeIface *iface;
 128
 129   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 130
 131   iface = G_VOLUME_GET_IFACE (volume);
 132
 133   return (* iface->get_name) (volume);
 134 }
 135
 136 /**
 137  * g_volume_get_icon:
 138  * @volume: a #GVolume
 139  *
 140  * Gets the icon for @volume.
 141  *
 142  * Returns: (transfer full): a #GIcon.
 143  *     The returned object should be unreffed with g_object_unref()
 144  *     when no longer needed.
 145  */
 146 GIcon *
 147 g_volume_get_icon (GVolume *volume)
 148 {
 149   GVolumeIface *iface;
 150
 151   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 152
 153   iface = G_VOLUME_GET_IFACE (volume);
 154
 155   return (* iface->get_icon) (volume);
 156 }
 157
 158 /**
 159  * g_volume_get_symbolic_icon:
 160  * @volume: a #GVolume
 161  *
 162  * Gets the symbolic icon for @volume.
 163  *
 164  * Returns: (transfer full): a #GIcon.
 165  *     The returned object should be unreffed with g_object_unref()
 166  *     when no longer needed.
 167  *
 168  * Since: 2.34
 169  */
 170 GIcon *
 171 g_volume_get_symbolic_icon (GVolume *volume)
 172 {
 173   GVolumeIface *iface;
 174   GIcon *ret;
 175
 176   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 177
 178   iface = G_VOLUME_GET_IFACE (volume);
 179
 180   if (iface->get_symbolic_icon != NULL)
 181     ret = iface->get_symbolic_icon (volume);
 182   else
 183     ret = g_themed_icon_new_with_default_fallbacks ("folder-remote-symbolic");
 184
 185   return ret;
 186
 187 }
 188
 189 /**
 190  * g_volume_get_uuid:
 191  * @volume: a #GVolume
 192  *
 193  * Gets the UUID for the @volume. The reference is typically based on
 194  * the file system UUID for the volume in question and should be
 195  * considered an opaque string. Returns %NULL if there is no UUID
 196  * available.
 197  *
 198  * Returns: the UUID for @volume or %NULL if no UUID can be computed.
 199  *     The returned string should be freed with g_free()
 200  *     when no longer needed.
 201  */
 202 char *
 203 g_volume_get_uuid (GVolume *volume)
 204 {
 205   GVolumeIface *iface;
 206
 207   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 208
 209   iface = G_VOLUME_GET_IFACE (volume);
 210
 211   return (* iface->get_uuid) (volume);
 212 }
 213
 214 /**
 215  * g_volume_get_drive:
 216  * @volume: a #GVolume
 217  *
 218  * Gets the drive for the @volume.
 219  *
 220  * Returns: (transfer full): a #GDrive or %NULL if @volume is not
 221  *     associated with a drive. The returned object should be unreffed
 222  *     with g_object_unref() when no longer needed.
 223  */
 224 GDrive *
 225 g_volume_get_drive (GVolume *volume)
 226 {
 227   GVolumeIface *iface;
 228
 229   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 230
 231   iface = G_VOLUME_GET_IFACE (volume);
 232
 233   return (* iface->get_drive) (volume);
 234 }
 235
 236 /**
 237  * g_volume_get_mount:
 238  * @volume: a #GVolume
 239  *
 240  * Gets the mount for the @volume.
 241  *
 242  * Returns: (transfer full): a #GMount or %NULL if @volume isn't mounted.
 243  *     The returned object should be unreffed with g_object_unref()
 244  *     when no longer needed.
 245  */
 246 GMount *
 247 g_volume_get_mount (GVolume *volume)
 248 {
 249   GVolumeIface *iface;
 250
 251   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 252
 253   iface = G_VOLUME_GET_IFACE (volume);
 254
 255   return (* iface->get_mount) (volume);
 256 }
 257
 258
 259 /**
 260  * g_volume_can_mount:
 261  * @volume: a #GVolume
 262  *
 263  * Checks if a volume can be mounted.
 264  *
 265  * Returns: %TRUE if the @volume can be mounted. %FALSE otherwise
 266  */
 267 gboolean
 268 g_volume_can_mount (GVolume *volume)
 269 {
 270   GVolumeIface *iface;
 271
 272   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 273
 274   iface = G_VOLUME_GET_IFACE (volume);
 275
 276   if (iface->can_mount == NULL)
 277     return FALSE;
 278
 279   return (* iface->can_mount) (volume);
 280 }
 281
 282 /**
 283  * g_volume_can_eject:
 284  * @volume: a #GVolume
 285  *
 286  * Checks if a volume can be ejected.
 287  *
 288  * Returns: %TRUE if the @volume can be ejected. %FALSE otherwise
 289  */
 290 gboolean
 291 g_volume_can_eject (GVolume *volume)
 292 {
 293   GVolumeIface *iface;
 294
 295   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 296
 297   iface = G_VOLUME_GET_IFACE (volume);
 298
 299   if (iface->can_eject == NULL)
 300     return FALSE;
 301
 302   return (* iface->can_eject) (volume);
 303 }
 304
 305 /**
 306  * g_volume_should_automount:
 307  * @volume: a #GVolume
 308  *
 309  * Returns whether the volume should be automatically mounted.
 310  *
 311  * Returns: %TRUE if the volume should be automatically mounted
 312  */
 313 gboolean
 314 g_volume_should_automount (GVolume *volume)
 315 {
 316   GVolumeIface *iface;
 317
 318   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 319
 320   iface = G_VOLUME_GET_IFACE (volume);
 321
 322   if (iface->should_automount == NULL)
 323     return FALSE;
 324
 325   return (* iface->should_automount) (volume);
 326 }
 327
 328
 329 /**
 330  * g_volume_mount:
 331  * @volume: a #GVolume
 332  * @flags: flags affecting the operation
 333  * @mount_operation: (nullable): a #GMountOperation or %NULL to avoid user interaction
 334  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 335  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 336  * @user_data: user data that gets passed to @callback
 337  *
 338  * Mounts a volume. This is an asynchronous operation, and is
 339  * finished by calling g_volume_mount_finish() with the @volume
 340  * and #GAsyncResult returned in the @callback.
 341  *
 342  * Virtual: mount_fn
 343  */
 344 void
 345 g_volume_mount (GVolume             *volume,
 346                 GMountMountFlags     flags,
 347                 GMountOperation     *mount_operation,
 348                 GCancellable        *cancellable,
 349                 GAsyncReadyCallback  callback,
 350                 gpointer             user_data)
 351 {
 352   GVolumeIface *iface;
 353
 354   g_return_if_fail (G_IS_VOLUME (volume));
 355
 356   iface = G_VOLUME_GET_IFACE (volume);
 357
 358   if (iface->mount_fn == NULL)
 359     {
 360       g_task_report_new_error (volume, callback, user_data,
 361                                g_volume_mount,
 362                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 363                                _("volume doesn’t implement mount"));
 364       return;
 365     }
 366
 367   (* iface->mount_fn) (volume, flags, mount_operation, cancellable, callback, user_data);
 368 }
 369
 370 /**
 371  * g_volume_mount_finish:
 372  * @volume: a #GVolume
 373  * @result: a #GAsyncResult
 374  * @error: a #GError location to store an error, or %NULL to ignore
 375  *
 376  * Finishes mounting a volume. If any errors occurred during the operation,
 377  * @error will be set to contain the errors and %FALSE will be returned.
 378  *
 379  * If the mount operation succeeded, g_volume_get_mount() on @volume
 380  * is guaranteed to return the mount right after calling this
 381  * function; there's no need to listen for the 'mount-added' signal on
 382  * #GVolumeMonitor.
 383  *
 384  * Returns: %TRUE, %FALSE if operation failed
 385  */
 386 gboolean
 387 g_volume_mount_finish (GVolume       *volume,
 388                        GAsyncResult  *result,
 389                        GError       **error)
 390 {
 391   GVolumeIface *iface;
 392
 393   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 394   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 395
 396   if (g_async_result_legacy_propagate_error (result, error))
 397     return FALSE;
 398   else if (g_async_result_is_tagged (result, g_volume_mount))
 399     return g_task_propagate_boolean (G_TASK (result), error);
 400
 401   iface = G_VOLUME_GET_IFACE (volume);
 402   return (* iface->mount_finish) (volume, result, error);
 403 }
 404
 405 /**
 406  * g_volume_eject:
 407  * @volume: a #GVolume
 408  * @flags: flags affecting the unmount if required for eject
 409  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 410  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 411  * @user_data: user data that gets passed to @callback
 412  *
 413  * Ejects a volume. This is an asynchronous operation, and is
 414  * finished by calling g_volume_eject_finish() with the @volume
 415  * and #GAsyncResult returned in the @callback.
 416  *
 417  * Deprecated: 2.22: Use g_volume_eject_with_operation() instead.
 418  */
 419 void
 420 g_volume_eject (GVolume             *volume,
 421                 GMountUnmountFlags   flags,
 422                 GCancellable        *cancellable,
 423                 GAsyncReadyCallback  callback,
 424                 gpointer             user_data)
 425 {
 426   GVolumeIface *iface;
 427
 428   g_return_if_fail (G_IS_VOLUME (volume));
 429
 430   iface = G_VOLUME_GET_IFACE (volume);
 431
 432   if (iface->eject == NULL)
 433     {
 434       g_task_report_new_error (volume, callback, user_data,
 435                                g_volume_eject_with_operation,
 436                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 437                                _("volume doesn’t implement eject"));
 438       return;
 439     }
 440
 441   (* iface->eject) (volume, flags, cancellable, callback, user_data);
 442 }
 443
 444 /**
 445  * g_volume_eject_finish:
 446  * @volume: pointer to a #GVolume
 447  * @result: a #GAsyncResult
 448  * @error: a #GError location to store an error, or %NULL to ignore
 449  *
 450  * Finishes ejecting a volume. If any errors occurred during the operation,
 451  * @error will be set to contain the errors and %FALSE will be returned.
 452  *
 453  * Returns: %TRUE, %FALSE if operation failed
 454  *
 455  * Deprecated: 2.22: Use g_volume_eject_with_operation_finish() instead.
 456  **/
 457 gboolean
 458 g_volume_eject_finish (GVolume       *volume,
 459                        GAsyncResult  *result,
 460                        GError       **error)
 461 {
 462   GVolumeIface *iface;
 463
 464   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 465   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 466
 467   if (g_async_result_legacy_propagate_error (result, error))
 468     return FALSE;
 469   if (g_async_result_is_tagged (result, g_volume_eject_with_operation))
 470     return g_task_propagate_boolean (G_TASK (result), error);
 471
 472   iface = G_VOLUME_GET_IFACE (volume);
 473   return (* iface->eject_finish) (volume, result, error);
 474 }
 475
 476 /**
 477  * g_volume_eject_with_operation:
 478  * @volume: a #GVolume
 479  * @flags: flags affecting the unmount if required for eject
 480  * @mount_operation: (nullable): a #GMountOperation or %NULL to
 481  *     avoid user interaction
 482  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 483  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 484  * @user_data: user data passed to @callback
 485  *
 486  * Ejects a volume. This is an asynchronous operation, and is
 487  * finished by calling g_volume_eject_with_operation_finish() with the @volume
 488  * and #GAsyncResult data returned in the @callback.
 489  *
 490  * Since: 2.22
 491  **/
 492 void
 493 g_volume_eject_with_operation (GVolume              *volume,
 494                                GMountUnmountFlags   flags,
 495                                GMountOperation     *mount_operation,
 496                                GCancellable        *cancellable,
 497                                GAsyncReadyCallback  callback,
 498                                gpointer             user_data)
 499 {
 500   GVolumeIface *iface;
 501
 502   g_return_if_fail (G_IS_VOLUME (volume));
 503
 504   iface = G_VOLUME_GET_IFACE (volume);
 505
 506   if (iface->eject == NULL && iface->eject_with_operation == NULL)
 507     {
 508       g_task_report_new_error (volume, callback, user_data,
 509                                g_volume_eject_with_operation,
 510                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 511                                /* Translators: This is an error
 512                                 * message for volume objects that
 513                                 * don't implement any of eject or eject_with_operation. */
 514                                _("volume doesn’t implement eject or eject_with_operation"));
 515       return;
 516     }
 517
 518   if (iface->eject_with_operation != NULL)
 519     (* iface->eject_with_operation) (volume, flags, mount_operation, cancellable, callback, user_data);
 520   else
 521     (* iface->eject) (volume, flags, cancellable, callback, user_data);
 522 }
 523
 524 /**
 525  * g_volume_eject_with_operation_finish:
 526  * @volume: a #GVolume
 527  * @result: a #GAsyncResult
 528  * @error: a #GError location to store the error occurring, or %NULL
 529  *
 530  * Finishes ejecting a volume. If any errors occurred during the operation,
 531  * @error will be set to contain the errors and %FALSE will be returned.
 532  *
 533  * Returns: %TRUE if the volume was successfully ejected. %FALSE otherwise
 534  *
 535  * Since: 2.22
 536  **/
 537 gboolean
 538 g_volume_eject_with_operation_finish (GVolume        *volume,
 539                                       GAsyncResult  *result,
 540                                       GError       **error)
 541 {
 542   GVolumeIface *iface;
 543
 544   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 545   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 546
 547   if (g_async_result_legacy_propagate_error (result, error))
 548     return FALSE;
 549   else if (g_async_result_is_tagged (result, g_volume_eject_with_operation))
 550     return g_task_propagate_boolean (G_TASK (result), error);
 551
 552   iface = G_VOLUME_GET_IFACE (volume);
 553   if (iface->eject_with_operation_finish != NULL)
 554     return (* iface->eject_with_operation_finish) (volume, result, error);
 555   else
 556     return (* iface->eject_finish) (volume, result, error);
 557 }
 558
 559 /**
 560  * g_volume_get_identifier:
 561  * @volume: a #GVolume
 562  * @kind: the kind of identifier to return
 563  *
 564  * Gets the identifier of the given kind for @volume.
 565  * See the [introduction][volume-identifier] for more
 566  * information about volume identifiers.
 567  *
 568  * Returns: a newly allocated string containing the
 569  *     requested identfier, or %NULL if the #GVolume
 570  *     doesn't have this kind of identifier
 571  */
 572 char *
 573 g_volume_get_identifier (GVolume    *volume,
 574                          const char *kind)
 575 {
 576   GVolumeIface *iface;
 577
 578   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 579   g_return_val_if_fail (kind != NULL, NULL);
 580
 581   iface = G_VOLUME_GET_IFACE (volume);
 582
 583   if (iface->get_identifier == NULL)
 584     return NULL;
 585
 586   return (* iface->get_identifier) (volume, kind);
 587 }
 588
 589 /**
 590  * g_volume_enumerate_identifiers:
 591  * @volume: a #GVolume
 592  *
 593  * Gets the kinds of [identifiers][volume-identifier] that @volume has.
 594  * Use g_volume_get_identifier() to obtain the identifiers themselves.
 595  *
 596  * Returns: (array zero-terminated=1) (transfer full): a %NULL-terminated array
 597  *   of strings containing kinds of identifiers. Use g_strfreev() to free.
 598  */
 599 char **
 600 g_volume_enumerate_identifiers (GVolume *volume)
 601 {
 602   GVolumeIface *iface;
 603
 604   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 605   iface = G_VOLUME_GET_IFACE (volume);
 606
 607   if (iface->enumerate_identifiers == NULL)
 608     return NULL;
 609
 610   return (* iface->enumerate_identifiers) (volume);
 611 }
 612
 613 /**
 614  * g_volume_get_activation_root:
 615  * @volume: a #GVolume
 616  *
 617  * Gets the activation root for a #GVolume if it is known ahead of
 618  * mount time. Returns %NULL otherwise. If not %NULL and if @volume
 619  * is mounted, then the result of g_mount_get_root() on the
 620  * #GMount object obtained from g_volume_get_mount() will always
 621  * either be equal or a prefix of what this function returns. In
 622  * other words, in code
 623  *
 624  * |[<!-- language="C" -->
 625  *   GMount *mount;
 626  *   GFile *mount_root
 627  *   GFile *volume_activation_root;
 628  *
 629  *   mount = g_volume_get_mount (volume); // mounted, so never NULL
 630  *   mount_root = g_mount_get_root (mount);
 631  *   volume_activation_root = g_volume_get_activation_root (volume); // assume not NULL
 632  * ]|
 633  * then the expression
 634  * |[<!-- language="C" -->
 635  *   (g_file_has_prefix (volume_activation_root, mount_root) ||
 636       g_file_equal (volume_activation_root, mount_root))
 637  * ]|
 638  * will always be %TRUE.
 639  *
 640  * Activation roots are typically used in #GVolumeMonitor
 641  * implementations to find the underlying mount to shadow, see
 642  * g_mount_is_shadowed() for more details.
 643  *
 644  * Returns: (nullable) (transfer full): the activation root of @volume
 645  *     or %NULL. Use g_object_unref() to free.
 646  *
 647  * Since: 2.18
 648  */
 649 GFile *
 650 g_volume_get_activation_root (GVolume *volume)
 651 {
 652   GVolumeIface *iface;
 653
 654   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 655   iface = G_VOLUME_GET_IFACE (volume);
 656
 657   if (iface->get_activation_root == NULL)
 658     return NULL;
 659
 660   return (* iface->get_activation_root) (volume);
 661 }
 662
 663 /**
 664  * g_volume_get_sort_key:
 665  * @volume: a #GVolume
 666  *
 667  * Gets the sort key for @volume, if any.
 668  *
 669  * Returns: Sorting key for @volume or %NULL if no such key is available
 670  *
 671  * Since: 2.32
 672  */
 673 const gchar *
 674 g_volume_get_sort_key (GVolume *volume)
 675 {
 676   const gchar *ret = NULL;
 677   GVolumeIface *iface;
 678
 679   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 680
 681   iface = G_VOLUME_GET_IFACE (volume);
 682   if (iface->get_sort_key != NULL)
 683     ret = iface->get_sort_key (volume);
 684
 685   return ret;
 686 }