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_UUID, #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: (nullable) (transfer full): the UUID for @volume or %NULL if no UUID
 199  *     can be computed.
 200  *     The returned string should be freed with g_free()
 201  *     when no longer needed.
 202  */
 203 char *
 204 g_volume_get_uuid (GVolume *volume)
 205 {
 206   GVolumeIface *iface;
 207
 208   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 209
 210   iface = G_VOLUME_GET_IFACE (volume);
 211
 212   return (* iface->get_uuid) (volume);
 213 }
 214
 215 /**
 216  * g_volume_get_drive:
 217  * @volume: a #GVolume
 218  *
 219  * Gets the drive for the @volume.
 220  *
 221  * Returns: (transfer full) (nullable): a #GDrive or %NULL if @volume is not
 222  *     associated with a drive. The returned object should be unreffed
 223  *     with g_object_unref() when no longer needed.
 224  */
 225 GDrive *
 226 g_volume_get_drive (GVolume *volume)
 227 {
 228   GVolumeIface *iface;
 229
 230   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 231
 232   iface = G_VOLUME_GET_IFACE (volume);
 233
 234   return (* iface->get_drive) (volume);
 235 }
 236
 237 /**
 238  * g_volume_get_mount:
 239  * @volume: a #GVolume
 240  *
 241  * Gets the mount for the @volume.
 242  *
 243  * Returns: (transfer full) (nullable): a #GMount or %NULL if @volume isn't mounted.
 244  *     The returned object should be unreffed with g_object_unref()
 245  *     when no longer needed.
 246  */
 247 GMount *
 248 g_volume_get_mount (GVolume *volume)
 249 {
 250   GVolumeIface *iface;
 251
 252   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 253
 254   iface = G_VOLUME_GET_IFACE (volume);
 255
 256   return (* iface->get_mount) (volume);
 257 }
 258
 259
 260 /**
 261  * g_volume_can_mount:
 262  * @volume: a #GVolume
 263  *
 264  * Checks if a volume can be mounted.
 265  *
 266  * Returns: %TRUE if the @volume can be mounted. %FALSE otherwise
 267  */
 268 gboolean
 269 g_volume_can_mount (GVolume *volume)
 270 {
 271   GVolumeIface *iface;
 272
 273   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 274
 275   iface = G_VOLUME_GET_IFACE (volume);
 276
 277   if (iface->can_mount == NULL)
 278     return FALSE;
 279
 280   return (* iface->can_mount) (volume);
 281 }
 282
 283 /**
 284  * g_volume_can_eject:
 285  * @volume: a #GVolume
 286  *
 287  * Checks if a volume can be ejected.
 288  *
 289  * Returns: %TRUE if the @volume can be ejected. %FALSE otherwise
 290  */
 291 gboolean
 292 g_volume_can_eject (GVolume *volume)
 293 {
 294   GVolumeIface *iface;
 295
 296   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 297
 298   iface = G_VOLUME_GET_IFACE (volume);
 299
 300   if (iface->can_eject == NULL)
 301     return FALSE;
 302
 303   return (* iface->can_eject) (volume);
 304 }
 305
 306 /**
 307  * g_volume_should_automount:
 308  * @volume: a #GVolume
 309  *
 310  * Returns whether the volume should be automatically mounted.
 311  *
 312  * Returns: %TRUE if the volume should be automatically mounted
 313  */
 314 gboolean
 315 g_volume_should_automount (GVolume *volume)
 316 {
 317   GVolumeIface *iface;
 318
 319   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 320
 321   iface = G_VOLUME_GET_IFACE (volume);
 322
 323   if (iface->should_automount == NULL)
 324     return FALSE;
 325
 326   return (* iface->should_automount) (volume);
 327 }
 328
 329
 330 /**
 331  * g_volume_mount:
 332  * @volume: a #GVolume
 333  * @flags: flags affecting the operation
 334  * @mount_operation: (nullable): a #GMountOperation or %NULL to avoid user interaction
 335  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 336  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 337  * @user_data: user data that gets passed to @callback
 338  *
 339  * Mounts a volume. This is an asynchronous operation, and is
 340  * finished by calling g_volume_mount_finish() with the @volume
 341  * and #GAsyncResult returned in the @callback.
 342  *
 343  * Virtual: mount_fn
 344  */
 345 void
 346 g_volume_mount (GVolume             *volume,
 347                 GMountMountFlags     flags,
 348                 GMountOperation     *mount_operation,
 349                 GCancellable        *cancellable,
 350                 GAsyncReadyCallback  callback,
 351                 gpointer             user_data)
 352 {
 353   GVolumeIface *iface;
 354
 355   g_return_if_fail (G_IS_VOLUME (volume));
 356
 357   iface = G_VOLUME_GET_IFACE (volume);
 358
 359   if (iface->mount_fn == NULL)
 360     {
 361       g_task_report_new_error (volume, callback, user_data,
 362                                g_volume_mount,
 363                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 364                                _("volume doesn’t implement mount"));
 365       return;
 366     }
 367
 368   (* iface->mount_fn) (volume, flags, mount_operation, cancellable, callback, user_data);
 369 }
 370
 371 /**
 372  * g_volume_mount_finish:
 373  * @volume: a #GVolume
 374  * @result: a #GAsyncResult
 375  * @error: a #GError location to store an error, or %NULL to ignore
 376  *
 377  * Finishes mounting a volume. If any errors occurred during the operation,
 378  * @error will be set to contain the errors and %FALSE will be returned.
 379  *
 380  * If the mount operation succeeded, g_volume_get_mount() on @volume
 381  * is guaranteed to return the mount right after calling this
 382  * function; there's no need to listen for the 'mount-added' signal on
 383  * #GVolumeMonitor.
 384  *
 385  * Returns: %TRUE, %FALSE if operation failed
 386  */
 387 gboolean
 388 g_volume_mount_finish (GVolume       *volume,
 389                        GAsyncResult  *result,
 390                        GError       **error)
 391 {
 392   GVolumeIface *iface;
 393
 394   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 395   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 396
 397   if (g_async_result_legacy_propagate_error (result, error))
 398     return FALSE;
 399   else if (g_async_result_is_tagged (result, g_volume_mount))
 400     return g_task_propagate_boolean (G_TASK (result), error);
 401
 402   iface = G_VOLUME_GET_IFACE (volume);
 403   return (* iface->mount_finish) (volume, result, error);
 404 }
 405
 406 /**
 407  * g_volume_eject:
 408  * @volume: a #GVolume
 409  * @flags: flags affecting the unmount if required for eject
 410  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 411  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 412  * @user_data: user data that gets passed to @callback
 413  *
 414  * Ejects a volume. This is an asynchronous operation, and is
 415  * finished by calling g_volume_eject_finish() with the @volume
 416  * and #GAsyncResult returned in the @callback.
 417  *
 418  * Deprecated: 2.22: Use g_volume_eject_with_operation() instead.
 419  */
 420 void
 421 g_volume_eject (GVolume             *volume,
 422                 GMountUnmountFlags   flags,
 423                 GCancellable        *cancellable,
 424                 GAsyncReadyCallback  callback,
 425                 gpointer             user_data)
 426 {
 427   GVolumeIface *iface;
 428
 429   g_return_if_fail (G_IS_VOLUME (volume));
 430
 431   iface = G_VOLUME_GET_IFACE (volume);
 432
 433   if (iface->eject == NULL)
 434     {
 435       g_task_report_new_error (volume, callback, user_data,
 436                                g_volume_eject_with_operation,
 437                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 438                                _("volume doesn’t implement eject"));
 439       return;
 440     }
 441
 442   (* iface->eject) (volume, flags, cancellable, callback, user_data);
 443 }
 444
 445 /**
 446  * g_volume_eject_finish:
 447  * @volume: pointer to a #GVolume
 448  * @result: a #GAsyncResult
 449  * @error: a #GError location to store an error, or %NULL to ignore
 450  *
 451  * Finishes ejecting a volume. If any errors occurred during the operation,
 452  * @error will be set to contain the errors and %FALSE will be returned.
 453  *
 454  * Returns: %TRUE, %FALSE if operation failed
 455  *
 456  * Deprecated: 2.22: Use g_volume_eject_with_operation_finish() instead.
 457  **/
 458 gboolean
 459 g_volume_eject_finish (GVolume       *volume,
 460                        GAsyncResult  *result,
 461                        GError       **error)
 462 {
 463   GVolumeIface *iface;
 464
 465   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 466   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 467
 468   if (g_async_result_legacy_propagate_error (result, error))
 469     return FALSE;
 470   if (g_async_result_is_tagged (result, g_volume_eject_with_operation))
 471     return g_task_propagate_boolean (G_TASK (result), error);
 472
 473   iface = G_VOLUME_GET_IFACE (volume);
 474   return (* iface->eject_finish) (volume, result, error);
 475 }
 476
 477 /**
 478  * g_volume_eject_with_operation:
 479  * @volume: a #GVolume
 480  * @flags: flags affecting the unmount if required for eject
 481  * @mount_operation: (nullable): a #GMountOperation or %NULL to
 482  *     avoid user interaction
 483  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore
 484  * @callback: (nullable): a #GAsyncReadyCallback, or %NULL
 485  * @user_data: user data passed to @callback
 486  *
 487  * Ejects a volume. This is an asynchronous operation, and is
 488  * finished by calling g_volume_eject_with_operation_finish() with the @volume
 489  * and #GAsyncResult data returned in the @callback.
 490  *
 491  * Since: 2.22
 492  **/
 493 void
 494 g_volume_eject_with_operation (GVolume              *volume,
 495                                GMountUnmountFlags   flags,
 496                                GMountOperation     *mount_operation,
 497                                GCancellable        *cancellable,
 498                                GAsyncReadyCallback  callback,
 499                                gpointer             user_data)
 500 {
 501   GVolumeIface *iface;
 502
 503   g_return_if_fail (G_IS_VOLUME (volume));
 504
 505   iface = G_VOLUME_GET_IFACE (volume);
 506
 507   if (iface->eject == NULL && iface->eject_with_operation == NULL)
 508     {
 509       g_task_report_new_error (volume, callback, user_data,
 510                                g_volume_eject_with_operation,
 511                                G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
 512                                /* Translators: This is an error
 513                                 * message for volume objects that
 514                                 * don't implement any of eject or eject_with_operation. */
 515                                _("volume doesn’t implement eject or eject_with_operation"));
 516       return;
 517     }
 518
 519   if (iface->eject_with_operation != NULL)
 520     (* iface->eject_with_operation) (volume, flags, mount_operation, cancellable, callback, user_data);
 521   else
 522     (* iface->eject) (volume, flags, cancellable, callback, user_data);
 523 }
 524
 525 /**
 526  * g_volume_eject_with_operation_finish:
 527  * @volume: a #GVolume
 528  * @result: a #GAsyncResult
 529  * @error: a #GError location to store the error occurring, or %NULL
 530  *
 531  * Finishes ejecting a volume. If any errors occurred during the operation,
 532  * @error will be set to contain the errors and %FALSE will be returned.
 533  *
 534  * Returns: %TRUE if the volume was successfully ejected. %FALSE otherwise
 535  *
 536  * Since: 2.22
 537  **/
 538 gboolean
 539 g_volume_eject_with_operation_finish (GVolume        *volume,
 540                                       GAsyncResult  *result,
 541                                       GError       **error)
 542 {
 543   GVolumeIface *iface;
 544
 545   g_return_val_if_fail (G_IS_VOLUME (volume), FALSE);
 546   g_return_val_if_fail (G_IS_ASYNC_RESULT (result), FALSE);
 547
 548   if (g_async_result_legacy_propagate_error (result, error))
 549     return FALSE;
 550   else if (g_async_result_is_tagged (result, g_volume_eject_with_operation))
 551     return g_task_propagate_boolean (G_TASK (result), error);
 552
 553   iface = G_VOLUME_GET_IFACE (volume);
 554   if (iface->eject_with_operation_finish != NULL)
 555     return (* iface->eject_with_operation_finish) (volume, result, error);
 556   else
 557     return (* iface->eject_finish) (volume, result, error);
 558 }
 559
 560 /**
 561  * g_volume_get_identifier:
 562  * @volume: a #GVolume
 563  * @kind: the kind of identifier to return
 564  *
 565  * Gets the identifier of the given kind for @volume.
 566  * See the [introduction][volume-identifier] for more
 567  * information about volume identifiers.
 568  *
 569  * Returns: (nullable) (transfer full): a newly allocated string containing the
 570  *     requested identifier, or %NULL if the #GVolume
 571  *     doesn't have this kind of identifier
 572  */
 573 char *
 574 g_volume_get_identifier (GVolume    *volume,
 575                          const char *kind)
 576 {
 577   GVolumeIface *iface;
 578
 579   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 580   g_return_val_if_fail (kind != NULL, NULL);
 581
 582   iface = G_VOLUME_GET_IFACE (volume);
 583
 584   if (iface->get_identifier == NULL)
 585     return NULL;
 586
 587   return (* iface->get_identifier) (volume, kind);
 588 }
 589
 590 /**
 591  * g_volume_enumerate_identifiers:
 592  * @volume: a #GVolume
 593  *
 594  * Gets the kinds of [identifiers][volume-identifier] that @volume has.
 595  * Use g_volume_get_identifier() to obtain the identifiers themselves.
 596  *
 597  * Returns: (array zero-terminated=1) (transfer full): a %NULL-terminated array
 598  *   of strings containing kinds of identifiers. Use g_strfreev() to free.
 599  */
 600 char **
 601 g_volume_enumerate_identifiers (GVolume *volume)
 602 {
 603   GVolumeIface *iface;
 604
 605   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 606   iface = G_VOLUME_GET_IFACE (volume);
 607
 608   if (iface->enumerate_identifiers == NULL)
 609     return NULL;
 610
 611   return (* iface->enumerate_identifiers) (volume);
 612 }
 613
 614 /**
 615  * g_volume_get_activation_root:
 616  * @volume: a #GVolume
 617  *
 618  * Gets the activation root for a #GVolume if it is known ahead of
 619  * mount time. Returns %NULL otherwise. If not %NULL and if @volume
 620  * is mounted, then the result of g_mount_get_root() on the
 621  * #GMount object obtained from g_volume_get_mount() will always
 622  * either be equal or a prefix of what this function returns. In
 623  * other words, in code
 624  *
 625  * |[<!-- language="C" -->
 626  *   GMount *mount;
 627  *   GFile *mount_root
 628  *   GFile *volume_activation_root;
 629  *
 630  *   mount = g_volume_get_mount (volume); // mounted, so never NULL
 631  *   mount_root = g_mount_get_root (mount);
 632  *   volume_activation_root = g_volume_get_activation_root (volume); // assume not NULL
 633  * ]|
 634  * then the expression
 635  * |[<!-- language="C" -->
 636  *   (g_file_has_prefix (volume_activation_root, mount_root) ||
 637  *    g_file_equal (volume_activation_root, mount_root))
 638  * ]|
 639  * will always be %TRUE.
 640  *
 641  * Activation roots are typically used in #GVolumeMonitor
 642  * implementations to find the underlying mount to shadow, see
 643  * g_mount_is_shadowed() for more details.
 644  *
 645  * Returns: (nullable) (transfer full): the activation root of @volume
 646  *     or %NULL. Use g_object_unref() to free.
 647  *
 648  * Since: 2.18
 649  */
 650 GFile *
 651 g_volume_get_activation_root (GVolume *volume)
 652 {
 653   GVolumeIface *iface;
 654
 655   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 656   iface = G_VOLUME_GET_IFACE (volume);
 657
 658   if (iface->get_activation_root == NULL)
 659     return NULL;
 660
 661   return (* iface->get_activation_root) (volume);
 662 }
 663
 664 /**
 665  * g_volume_get_sort_key:
 666  * @volume: a #GVolume
 667  *
 668  * Gets the sort key for @volume, if any.
 669  *
 670  * Returns: (nullable): Sorting key for @volume or %NULL if no such key is available
 671  *
 672  * Since: 2.32
 673  */
 674 const gchar *
 675 g_volume_get_sort_key (GVolume *volume)
 676 {
 677   const gchar *ret = NULL;
 678   GVolumeIface *iface;
 679
 680   g_return_val_if_fail (G_IS_VOLUME (volume), NULL);
 681
 682   iface = G_VOLUME_GET_IFACE (volume);
 683   if (iface->get_sort_key != NULL)
 684     ret = iface->get_sort_key (volume);
 685
 686   return ret;
 687 }