[tracker] tracker-file-utils.c: dlopen("libblkid.so.1")

Only two functions are needed from libblkid:
- blkid_get_cache()
- blkid_get_tag_value()

dlopen() the library instead of linking directly to it, and define the
necessary structs and function prototypes here. This removes the need
for the libblkid-dev dependency at build time.

NOTE: libblkid.so.1 is *not* dlclose()'d. This shouldn't be a problem,
since Tracker uses it directly anyway.

debian/control

@@ -33,8 +33,7 @@ Build-Depends:
  gettext,
  liblz4-dev,
  liblzo2-dev,
- libgsound-dev,
- libblkid-dev
+ libgsound-dev
 Standards-Version: 3.9.8
 Homepage: https://github.com/GerbilSoft/rom-properties
 Vcs-Git: https://github.com/GerbilSoft/rom-properties

doc/COMPILING.md

@@ -12,7 +12,6 @@ packages:
 * XFCE (GTK+ 3.x): libglib2.0-dev libgtk-3-dev libcairo2-dev libthunarx-3-dev libgsound-dev
 * GNOME, MATE, Cinnamon: libglib2.0-dev libgtk-3-dev libcairo2-dev libnautilus-extension-dev libgsound-dev
 * GNOME 43: libglib2.0-dev libgtk-4-dev libgdk-pixbuf2.0-dev libnautilus-extension-dev libgsound-dev
-* GNOME Tracker: libblkid-dev
 
 NOTE: On older versions of Ubuntu, some packages were different:
 * Earlier than 18.04:

src/gtk/tracker/CMakeLists.txt

@@ -6,14 +6,13 @@ FIND_PACKAGE(GLib2 ${REQUIRE_XFCE} ${GLIB_MIN_VERSION})
 FIND_PACKAGE(GObject2 ${REQUIRE_XFCE} ${GLIB_MIN_VERSION})
 FIND_PACKAGE(GIO ${REQUIRE_XFCE} ${GLIB_MIN_VERSION})
 FIND_PACKAGE(GIO-UNIX ${REQUIRE_XFCE} ${GLIB_MIN_VERSION})
-FIND_PACKAGE(Blkid)
-IF(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND AND Blkid_FOUND)
+IF(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND)
 	# All required libraries were found.
-ELSE(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND AND Blkid_FOUND)
+ELSE(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND)
 	# A required library was not found.
 	# Disable the Tracker extractor.
 	SET(BUILD_TRACKER_EXTRACTOR OFF CACHE INTERNAL "Build the Tracker extractor module." FORCE)
-ENDIF(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND AND Blkid_FOUND)
+ENDIF(GLib2_FOUND AND GObject2_FOUND AND GIO_FOUND AND GIO-UNIX_FOUND)
 
 # Ensure we don't use functions not available in GLib 2.34.
 ADD_DEFINITIONS(-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_34 -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_34)
@@ -55,7 +54,6 @@ IF(BUILD_TRACKER_EXTRACTOR)
 	TARGET_LINK_LIBRARIES(${PROJECT_NAME} PRIVATE unixcommon rpsecure)
 	TARGET_LINK_LIBRARIES(${PROJECT_NAME} PRIVATE romdata)
 	TARGET_LINK_LIBRARIES(${PROJECT_NAME} PRIVATE GLib2::gio-unix GLib2::gio GLib2::gobject GLib2::glib)
-	TARGET_LINK_LIBRARIES(${PROJECT_NAME} PRIVATE Blkid::blkid)
 	# Link in libdl if it's required for dlopen().
 	IF(CMAKE_DL_LIBS)
 		TARGET_LINK_LIBRARIES(${PROJECT_NAME} PRIVATE ${CMAKE_DL_LIBS})

src/gtk/tracker/tracker-file-utils.c

@@ -14,7 +14,7 @@
 #include "tracker-file-utils.h"
 
 #include <gio/gunixmounts.h>
-#include <blkid.h>
+//#include <blkid.h>
 
 #ifdef HAVE_BTRFS_IOCTL
 #  include <linux/btrfs.h>
@@ -23,6 +23,8 @@
 #endif
 
 // C includes
+#include <dlfcn.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <string.h>
 #include <unistd.h>
@@ -31,6 +33,22 @@
 // - g_autofree (2.44)
 // - g_unix_mount_monitor_get() (2.44)
 
+/** blkid/blkid.h **/
+
+// dlopen() pointers for libblkid
+// NOTE: Not dlclose()'d.
+static void *libblkid_so = NULL;
+
+typedef struct blkid_struct_cache *blkid_cache;
+
+extern int blkid_get_cache(blkid_cache *cache, const char *filename);
+extern char *blkid_get_tag_value(blkid_cache cache, const char *tagname, const char *devname);
+
+static __typeof__(blkid_get_cache) *pfn_blkid_get_cache = NULL;
+static __typeof__(blkid_get_tag_value) *pfn_blkid_get_tag_value = NULL;
+
+/** Original libtracker-miners-common code starts here **/
+
 typedef struct {
 	GFile *file;
 	gchar *mount_point;
@@ -82,7 +100,7 @@ update_mounts (TrackerUnixMountCache *cache)
 		UnixMountInfo mount;
 
 		devname = g_unix_mount_get_device_path (entry);
-		id = blkid_get_tag_value (cache->id_cache, "UUID", devname);
+		id = pfn_blkid_get_tag_value (cache->id_cache, "UUID", devname);
 		if (!id && strchr (devname, G_DIR_SEPARATOR) != NULL)
 			id = g_strdup (devname);
 
@@ -115,7 +133,7 @@ tracker_unix_mount_cache_get (void)
 		obj->mounts = g_array_new (FALSE, FALSE, sizeof (UnixMountInfo));
 		g_array_set_clear_func (obj->mounts, clear_mount_info);
 
-		blkid_get_cache (&obj->id_cache, NULL);
+		pfn_blkid_get_cache (&obj->id_cache, NULL);
 
 		/*g_signal_connect (obj->monitor, "mounts-changed",
 				  G_CALLBACK (on_mounts_changed), obj);*/
@@ -181,12 +199,55 @@ tracker_file_get_btrfs_subvolume_id (GFile *file)
 }
 #endif
 
+/**
+ * Attempt to initialize libblkid.so.
+ * @return 0 on success; negative POSIX error code on error.
+ */
+static int
+init_libblkid_so(void)
+{
+	if (libblkid_so) {
+		// Already initialized.
+		return 0;
+	}
+
+	// Attempt to dlopen() libblkid.so.
+	// NOTE: Not dlclose()'d.
+	libblkid_so = dlopen("libblkid.so.1", RTLD_NOW | RTLD_LOCAL);
+	if (!libblkid_so) {
+		// Not found...
+		// TODO: Other error?
+		return -ENOENT;
+	}
+
+	// Attempt to dlsym() the required symbols.
+	pfn_blkid_get_cache = dlsym(libblkid_so, "blkid_get_cache");
+	pfn_blkid_get_tag_value = dlsym(libblkid_so, "blkid_get_tag_value");
+	if (!pfn_blkid_get_cache || !pfn_blkid_get_tag_value) {
+		// One (or both) symbols are missing?
+		dlclose(libblkid_so);
+		pfn_blkid_get_cache = NULL;
+		pfn_blkid_get_tag_value = NULL;
+		libblkid_so = NULL;
+		return -EIO;
+	}
+
+	// Symbols loaded.
+	return 0;
+}
+
 gchar *
 tracker_file_get_content_identifier (GFile *file, GFileInfo *info, const gchar *suffix)
 {
 	const gchar *id;
 	/*g_autofree*/ gchar *inode = NULL, *str = NULL, *subvolume = NULL;
 
+	// Make sure libblkid.so is initialized.
+	if (init_libblkid_so() != 0) {
+		// Cannot initialize libblkid.so.
+		return NULL;
+	}
+
 	if (info) {
 		g_object_ref (info);
 	} else {