LibC: Implement if_indextoname and if_nametoindex

These are needed for our cmake port

userspace/libraries/LibC/CMakeLists.txt

@@ -20,6 +20,7 @@ set(LIBC_SOURCES
 	locale.cpp
 	malloc.cpp
 	math.cpp
+	net/if.cpp
 	netdb.cpp
 	netinet/in.cpp
 	poll.cpp

userspace/libraries/LibC/net/if.cpp

@@ -0,0 +1,71 @@
+#include <dirent.h>
+#include <net/if.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int selector(const dirent* dirent)
+{
+	if (strcmp(dirent->d_name, "lo") == 0)
+		return 1;
+	if (strncmp(dirent->d_name, "eth", 3) == 0)
+		return 1;
+	return 0;
+}
+
+static int comparator(const dirent** d1, const dirent** d2)
+{
+	if (strcmp((*d1)->d_name, "lo"))
+		return -1;
+	if (strcmp((*d2)->d_name, "lo"))
+		return +1;
+	return alphasort(d1, d2);
+}
+
+char* if_indextoname(unsigned ifindex, char* ifname)
+{
+	if (ifindex == 0)
+		return nullptr;
+
+	dirent** namelist;
+
+	const int count = scandir("/dev", &namelist, selector, comparator);
+	if (count == -1)
+		return nullptr;
+
+	char* result = nullptr;
+	if (ifindex - 1 < static_cast<unsigned>(count))
+	{
+		strcpy(ifname, namelist[ifindex - 1]->d_name);
+		result = ifname;
+	}
+
+	for (int i = 0; i < count; i++)
+		free(namelist[i]);
+	free(namelist);
+
+	return result;
+}
+
+unsigned if_nametoindex(const char* ifname)
+{
+	dirent** namelist;
+
+	const int count = scandir("/dev", &namelist, selector, comparator);
+	if (count == -1)
+		return 0;
+
+	unsigned result = 0;
+	for (int i = 0; i < count; i++)
+	{
+		if (strcmp(ifname, namelist[i]->d_name) != 0)
+			continue;
+		result = i + 1;
+		break;
+	}
+
+	for (int i = 0; i < count; i++)
+		free(namelist[i]);
+	free(namelist);
+
+	return result;
+}