Kernel+LibC+Userland: Start working on an IPv4 socket backend.

The first userland networking program will be "ping" :^)

Userland/ping.cpp

@@ -0,0 +1,58 @@
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <netinet/ip_icmp.h>
+#include <stdio.h>
+#include <string.h>
+#include <Kernel/NetworkOrdered.h>
+
+NetworkOrdered<word> internet_checksum(const void* ptr, size_t count)
+{
+    dword checksum = 0;
+    auto* w = (const word*)ptr;
+    while (count > 1) {
+        checksum += convert_between_host_and_network(*w++);
+        if (checksum & 0x80000000)
+            checksum = (checksum & 0xffff) | (checksum >> 16);
+        count -= 2;
+    }
+    while (checksum >> 16)
+        checksum = (checksum & 0xffff) + (checksum >> 16);
+    return ~checksum & 0xffff;
+}
+
+
+int main(int argc, char** argv)
+{
+    int fd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
+    if (fd < 0) {
+        perror("socket");
+        return 1;
+    }
+
+    sockaddr_in peer_address;
+    memset(&peer_address, 0, sizeof(peer_address));
+    peer_address.sin_family = AF_INET;
+    peer_address.sin_port = 0;
+    peer_address.sin_addr.s_addr = 0x0105a8c0; // 192.168.5.1
+
+    struct PingPacket {
+        struct icmphdr header;
+        char msg[64 - sizeof(struct icmphdr)];
+    };
+
+    PingPacket ping_packet;
+    memset(&ping_packet, 0, sizeof(PingPacket));
+
+    ping_packet.header.type = 8; // Echo request
+    strcpy(ping_packet.msg, "Hello there!\n");
+
+    ping_packet.header.checksum = htons(internet_checksum(&ping_packet, sizeof(PingPacket)));
+
+    int rc = sendto(fd, &ping_packet, sizeof(PingPacket), 0, (const struct sockaddr*)&peer_address, sizeof(sockaddr_in));
+    if (rc < 0) {
+        perror("sendto");
+        return 1;
+    }
+
+    return 0;
+}