plugins: modprobe: Support for coldplugging more devices

As it turns out, not all buses in Linux will add `modalias` attributes
to their devices in sysfs. One notable exception are MDIO buses. The
plugin's scan routine would thus not pick them up.

Fortunately, the information is always available in the device's
`uevent` attribute.

Therefore, default to looking for modaliases in the device's `uevent`
attribute instead, falling back to `modalias` only if `uevent` is not
availble (this should never happen).

plugins/modprobe.c

@@ -106,7 +106,7 @@ static void alias_remove(struct module *m)
 	TAILQ_REMOVE(&modules, m, link);
 	free(m->alias);
 	free(m);
-}	
+}
 
 static int alias_exist(char *alias)
 {
@@ -120,27 +120,88 @@ static int alias_exist(char *alias)
 	return 0;
 }
 
-static int scan_alias(const char *path, const struct stat *st, int flag, struct FTW *unused)
+static void alias_add_uniq(char *alias)
+{
+
+	if (alias_exist(alias))
+		return;
+
+	alias_add(alias);
+}
+
+static FILE *maybe_fopen_alias(const char *file, const char *path)
+{
+	const char *basename;
+
+	basename = rindex(path, '/');
+	if (!basename)
+		return NULL;
+
+	basename++;
+	if (strcmp(file, basename))
+		return NULL;
+
+	return fopen(path, "r");
+}
+
+static int scan_modalias(const char *path)
 {
 	FILE *fp;
 	char buf[256];
 
-	if (fnmatch("*/modalias", path, 0))
-		return 0;
-
-	fp = fopen(path, "r");
+	fp = maybe_fopen_alias("modalias", path);
 	if (!fp)
-		return 0;
+		return 1;
+
 	if (fgets(buf, sizeof(buf), fp)) {
 		chomp(buf);
-		if (!alias_exist(buf))
-			alias_add(buf);
+		alias_add_uniq(buf);
 	}
+
 	fclose(fp);
 
 	return 0;
 }
 
+static int scan_uevent(const char *path)
+{
+	FILE *fp;
+	char buf[256];
+
+	fp = maybe_fopen_alias("uevent", path);
+	if (!fp)
+		return 1;
+
+	while (fgets(buf, sizeof(buf), fp)) {
+		if (strstr(buf, "MODALIAS=") != buf)
+			continue;
+
+		chomp(buf);
+
+		alias_add_uniq(buf + strlen("MODALIAS="));
+		break;
+	}
+
+	fclose(fp);
+
+	return 0;
+}
+
+static int scan_alias(const char *path, const struct stat *st,
+		      int flag, struct FTW *unused)
+{
+	/* Perform some basic sanity checks first: that this is a
+	 * regular file that we can read. */
+	if (!(S_ISREG(st->st_mode) && (st->st_mode & S_IRUSR)))
+		return 0;
+
+	if (!scan_uevent(path))
+		return 0;
+
+	scan_modalias(path);
+	return 0;
+}
+
 static void coldplug(void *arg)
 {
 	struct module *m, *tmp;