udev_device.c: consider device valid even if no subsystem symlink exists

Some devices may not have subsystem symlinks, therefore we cannot rely
on that to check if device is valid. Instead, check uevent file which
should be always present in valid device.

Reference: openwrt/openwrt#12350

udev_device.c

@@ -342,17 +342,17 @@ static char *read_symlink(const char *syspath, const char *name)
     return strdup(strrchr(link, '/') + 1);
 }
 
-static void set_properties_from_uevent(struct udev_device *udev_device)
+static int set_properties_from_uevent(struct udev_device *udev_device, const char *syspath)
 {
-    char line[LINE_MAX], path[PATH_MAX], devnode[PATH_MAX];
+    char line[LINE_MAX], path[PATH_MAX + sizeof("/uevent")], devnode[PATH_MAX];
     FILE *file;
     char *pos;
 
-    snprintf(path, sizeof(path), "%s/uevent", udev_device_get_syspath(udev_device));
+    snprintf(path, sizeof(path), "%s/uevent", syspath);
     file = fopen(path, "r");
 
     if (!file) {
-        return;
+        return -1;
     }
 
     while (fgets(line, sizeof(line), file)) {
@@ -364,11 +364,12 @@ static void set_properties_from_uevent(struct udev_device *udev_device)
         }
         else if ((pos = strchr(line, '='))) {
             *pos = '\0';
-            udev_list_entry_add(&udev_device->properties, line, pos + 1, 1);
+            udev_list_entry_add(&udev_device->properties, line, pos + 1, 0);
         }
     }
 
     fclose(file);
+    return 0;
 }
 
 static void make_bit(unsigned long *arr, int cnt, const char *str)
@@ -543,21 +544,13 @@ struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *
         return NULL;
     }
 
-    subsystem = read_symlink(syspath, "subsystem");
-
-    if (!subsystem) {
-        return NULL;
-    }
-
     if (!realpath(syspath, path)) {
-        free(subsystem);
         return NULL;
     }
 
     udev_device = calloc(1, sizeof(*udev_device));
 
     if (!udev_device) {
-        free(subsystem);
         return NULL;
     }
 
@@ -568,11 +561,17 @@ struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *
     udev_list_entry_init(&udev_device->properties);
     udev_list_entry_init(&udev_device->sysattrs);
 
+    if (set_properties_from_uevent(udev_device, path) == -1) {
+        free(udev_device);
+        return NULL;
+    }
+
     udev_list_entry_add(&udev_device->properties, "SYSPATH", path, 0);
     udev_list_entry_add(&udev_device->properties, "DEVPATH", path + 4, 0);
 
     sysname = strrchr(path, '/') + 1;
     driver = read_symlink(path, "driver");
+    subsystem = read_symlink(path, "subsystem");
 
     udev_list_entry_add(&udev_device->properties, "SUBSYSTEM", subsystem, 0);
     udev_list_entry_add(&udev_device->properties, "SYSNAME", sysname, 0);
@@ -585,7 +584,6 @@ struct udev_device *udev_device_new_from_syspath(struct udev *udev, const char *
         }
     }
 
-    set_properties_from_uevent(udev_device);
     set_properties_from_evdev(udev_device);
     set_properties_from_props(udev_device);