libudev: add udev_device_new_from_devnum()

udev/lib/exported_symbols

@@ -8,6 +8,7 @@ udev_set_log_priority
 udev_get_sys_path
 udev_get_dev_path
 udev_device_new_from_syspath
+udev_device_new_from_devnum
 udev_device_get_parent
 udev_device_ref
 udev_device_unref

udev/lib/libudev-device.c

@@ -216,6 +216,20 @@ struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *
 	return udev_device;
 }
 
+struct udev_device *udev_device_new_from_devnum(struct udev *udev, char type, dev_t devnum)
+{
+	char path[UTIL_PATH_SIZE];
+
+	snprintf(path, sizeof(path), "%s/dev/%s/%u:%u",
+		 udev_get_sys_path(udev),
+		 type == 'b' ? "block" : "char",
+		 major(devnum), minor(devnum));
+	if (util_resolve_sys_link(udev, path, sizeof(path)) < 0)
+		return NULL;
+
+	return udev_device_new_from_syspath(udev, path);
+}
+
 static struct udev_device *device_new_from_parent(struct udev_device *udev_device)
 {
 	struct udev_device *udev_device_parent = NULL;

udev/lib/libudev-util.c

@@ -64,12 +64,17 @@ ssize_t util_get_sys_driver(struct udev *udev, const char *syspath, char *driver
 
 int util_resolve_sys_link(struct udev *udev, char *syspath, size_t size)
 {
+	struct stat statbuf;
 	char link_target[UTIL_PATH_SIZE];
 
 	int len;
 	int i;
 	int back;
 
+	if (lstat(syspath, &statbuf) < 0)
+		return -1;
+	if (!S_ISLNK(statbuf.st_mode))
+		return -1;
 	len = readlink(syspath, link_target, sizeof(link_target));
 	if (len <= 0)
 		return -1;

udev/lib/libudev.h

@@ -46,6 +46,7 @@ extern void udev_selinux_lsetfilecon(struct udev *udev, const char *file, unsign
 
 struct udev_device;
 extern struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *syspath);
+extern struct udev_device *udev_device_new_from_devnum(struct udev *udev, char type, dev_t devnum);
 extern struct udev_device *udev_device_get_parent(struct udev_device *udev_device);
 extern struct udev_device *udev_device_ref(struct udev_device *udev_device);
 extern void udev_device_unref(struct udev_device *udev_device);

udev/lib/test-libudev.c

@@ -24,6 +24,7 @@
 #include <string.h>
 #include <getopt.h>
 #include <syslog.h>
+#include <fcntl.h>
 #include <sys/select.h>
 
 #include "libudev.h"
@@ -114,6 +115,20 @@ static int test_device_parents(struct udev *udev, const char *syspath)
 	return 0;
 }
 
+static int test_device_devnum(struct udev *udev)
+{
+	dev_t devnum = makedev(1, 3);
+	struct udev_device *device;
+
+	printf("looking up device: %u:%u\n", major(devnum), minor(devnum));
+	device = udev_device_new_from_devnum(udev, 'c', devnum);
+	if (device == NULL)
+		return -1;
+	print_device(device);
+	udev_device_unref(device);
+	return 0;
+}
+
 static int devices_enum_cb(struct udev_device *device, void *data)
 {
 	printf("device:    '%s' (%s) '%s'\n",
@@ -253,6 +268,7 @@ int main(int argc, char *argv[], char *envp[])
 	}
 
 	test_device(udev, syspath);
+	test_device_devnum(udev);
 	test_device_parents(udev, syspath);
 	test_enumerate(udev, subsystem);
 	test_monitor(udev, socket);