Kernel: Cache MAC<->IP mappings (from ARP responses) seen on the wire.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/90f60d2f650

AK/StringImpl.cpp

@@ -155,20 +155,10 @@ slow_path:
 
 void StringImpl::compute_hash() const
 {
-    if (!length()) {
+    if (!length())
         m_hash = 0;
-    } else {
-        unsigned hash = 0;
-        for (ssize_t i = 0; i < m_length; ++i) {
-            hash += m_characters[i];
-            hash += (hash << 10);
-            hash ^= (hash >> 6);
-        }
-        hash += hash << 3;
-        hash ^= hash >> 11;
-        hash += hash << 15;
-        m_hash = hash;
-    }
+    else
+        m_hash = string_hash(m_characters, m_length);
     m_hasHash = true;
 }
 

AK/StringImpl.h

@@ -47,7 +47,22 @@ private:
     char m_inline_buffer[0];
 };
 
+inline dword string_hash(const char* characters, int length)
+{
+    dword hash = 0;
+    for (int i = 0; i < length; ++i) {
+        hash += (dword)characters[i];
+        hash += (hash << 10);
+        hash ^= (hash >> 6);
+    }
+    hash += hash << 3;
+    hash ^= hash >> 11;
+    hash += hash << 15;
+    return hash;
+}
+
 }
 
 using AK::StringImpl;
 using AK::Chomp;
+using AK::string_hash;

Kernel/IPv4Address.h

@@ -42,3 +42,13 @@ private:
 };
 
 static_assert(sizeof(IPv4Address) == 4);
+
+namespace AK {
+
+template<>
+struct Traits<IPv4Address> {
+    static unsigned hash(const IPv4Address& address) { return string_hash((const char*)&address, sizeof(address)); }
+    static void dump(const IPv4Address& address) { kprintf("%s", address.to_string().characters()); }
+};
+
+}

Kernel/MACAddress.h

@@ -20,6 +20,11 @@ public:
         return m_data[i];
     }
 
+    bool operator==(const MACAddress& other) const
+    {
+        return !memcmp(m_data, other.m_data, sizeof(m_data));
+    }
+
     String to_string() const
     {
         return String::format("%b:%b:%b:%b:%b:%b", m_data[0], m_data[1], m_data[2], m_data[3], m_data[4], m_data[5]);
@@ -30,3 +35,13 @@ private:
 };
 
 static_assert(sizeof(MACAddress) == 6);
+
+namespace AK {
+
+template<>
+struct Traits<MACAddress> {
+    static unsigned hash(const MACAddress& address) { return string_hash((const char*)&address, sizeof(address)); }
+    static void dump(const MACAddress& address) { kprintf("%s", address.to_string().characters()); }
+};
+
+}

Kernel/NetworkTask.cpp

@@ -3,10 +3,19 @@
 #include <Kernel/ARPPacket.h>
 #include <Kernel/Process.h>
 #include <Kernel/EtherType.h>
+#include <AK/Lock.h>
 
 static void handle_arp(const EthernetFrameHeader&, int frame_size);
 static void handle_ipv4(const EthernetFrameHeader&, int frame_size);
 
+Lockable<HashMap<IPv4Address, MACAddress>>& arp_table()
+{
+    static Lockable<HashMap<IPv4Address, MACAddress>>* the;
+    if (!the)
+        the = new Lockable<HashMap<IPv4Address, MACAddress>>;
+    return *the;
+}
+
 void NetworkTask_main()
 {
     auto* e1000_ptr = E1000NetworkAdapter::the();
@@ -59,7 +68,7 @@ void handle_arp(const EthernetFrameHeader& eth, int frame_size)
         kprintf("handle_arp: Frame too small (%d, need %d)\n", frame_size, minimum_arp_frame_size);
         return;
     }
-    const ARPPacket& packet = *static_cast<const ARPPacket*>(eth.payload());
+    auto& packet = *static_cast<const ARPPacket*>(eth.payload());
     if (packet.hardware_type() != 1 || packet.hardware_address_length() != sizeof(MACAddress)) {
         kprintf("handle_arp: Hardware type not ethernet (%w, len=%u)\n",
             packet.hardware_type(),
@@ -104,6 +113,20 @@ void handle_arp(const EthernetFrameHeader& eth, int frame_size)
 
             e1000.send(packet.sender_hardware_address(), response);
         }
+        return;
+    }
+
+    if (packet.operation() == 2) {
+        // Someone has this IPv4 address. I guess we can try to remember that.
+        // FIXME: Protect against ARP spamming.
+        // FIXME: Support static ARP table entries.
+        LOCKER(arp_table().lock());
+        arp_table().resource().set(packet.sender_protocol_address(), packet.sender_hardware_address());
+
+        kprintf("ARP table (%d entries):\n", arp_table().resource().size());
+        for (auto& it : arp_table().resource()) {
+            kprintf("%s :: %s\n", it.value.to_string().characters(), it.key.to_string().characters());
+        }
     }
 }