Add support for rt_protos.d

Add support for reading proto id/name mappings from rt_protos.d
directory. Allows users to have custom protocol values converted
to human friendly names.

Each file under rt_protos.d has the 'id name' format used by
rt_protos. Only .conf files are read and parsed.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>

etc/iproute2/rt_protos.d/README

@@ -0,0 +1,2 @@
+Each file in this directory is an rt_protos configuration file. iproute2
+commands scan this directory processing all files that end in '.conf'.

etc/iproute2/rt_tables.d/README

@@ -1,3 +1,2 @@
 Each file in this directory is an rt_tables configuration file. iproute2
 commands scan this directory processing all files that end in '.conf'.
-

lib/rt_names.c

@@ -142,9 +142,36 @@ static int rtnl_rtprot_init;
 
 static void rtnl_rtprot_initialize(void)
 {
+	struct dirent *de;
+	DIR *d;
+
 	rtnl_rtprot_init = 1;
 	rtnl_tab_initialize(CONFDIR "/rt_protos",
 			    rtnl_rtprot_tab, 256);
+
+	d = opendir(CONFDIR "/rt_protos.d");
+	if (!d)
+		return;
+
+	while ((de = readdir(d)) != NULL) {
+		char path[PATH_MAX];
+		size_t len;
+
+		if (*de->d_name == '.')
+			continue;
+
+		/* only consider filenames ending in '.conf' */
+		len = strlen(de->d_name);
+		if (len <= 5)
+			continue;
+		if (strcmp(de->d_name + len - 5, ".conf"))
+			continue;
+
+		snprintf(path, sizeof(path), CONFDIR "/rt_protos.d/%s",
+			 de->d_name);
+		rtnl_tab_initialize(path, rtnl_rtprot_tab, 256);
+	}
+	closedir(d);
 }
 
 const char *rtnl_rtprot_n2a(int id, char *buf, int len)