IT WORKS YIPPEEEE

Makefile

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+obj-m += postage.o

build.sh

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+make -C $(nix-build -E '(import <nixpkgs> {}).linux.dev' --no-out-link)/lib/modules/*/build M=$(pwd) modules

clean.sh

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+make -C $(nix-build -E '(import <nixpkgs> {}).linux.dev' --no-out-link)/lib/modules/*/build M=$(pwd) clean

postage.c

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+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/stddef.h>
+#include <linux/netdevice.h>
+
+MODULE_LICENSE("GPL");
+
+struct net_device *dev;
+
+static int my_eth_init(struct net_device *dev)
+{
+    // Initialize device
+    printk(KERN_INFO "My Ethernet device initialized\n");
+    netif_start_queue(dev);
+    return 0;
+
+}
+
+static void my_eth_exit(struct net_device *dev)
+{
+    // Cleanup device
+    pr_info(KERN_INFO "My Ethernet device exited\n");
+    netif_stop_queue(dev);
+}
+
+static netdev_tx_t my_eth_start_xmit(struct sk_buff *skb, 
+                             struct net_device *dev)
+{
+    // Start xmit
+    printk(KERN_INFO "My Ethernet device start xmit\n");
+    printk("len: %d\n", skb->len);
+    for (int i = 0; i < skb->len; i++) {
+        printk("data: %c\n", skb->data[i]);
+    }
+    printk("protocol: %d\n", skb->protocol);
+
+    netif_receive_skb(skb);
+
+    return NETDEV_TX_OK;
+}
+
+static struct net_device_ops my_netdev_ops = {
+    .ndo_init = my_eth_init,
+    .ndo_uninit = my_eth_exit,
+    .ndo_start_xmit = my_eth_start_xmit
+};
+
+void init_testcard(struct net_device *dev) 
+{
+    dev->netdev_ops = &my_netdev_ops;
+    printk("Init testcard\n");
+}
+
+struct net_device testcard;
+
+int register_device(void) {
+    dev = alloc_netdev(0, "myeth%d", NET_NAME_UNKNOWN, init_testcard);
+
+    if (!dev)
+        return -ENOMEM;
+
+    printk("Registering\n");
+
+    if (register_netdev(dev)) {
+        printk("Failed :(\n");
+        free_netdev(dev);
+        return -ENODEV;
+    }
+    
+    printk("Registered\n");
+    
+    return 0;
+}
+
+int __init custom_init(void)
+{
+    int err;
+    if ((err = register_device())) {
+        printk("Error loading postage\n");
+        return err;
+    }
+
+    return 0;
+}
+
+void __exit custom_exit(void)
+{
+    if (!dev) {
+        printk(KERN_ERR "Ethernet device not found\n");
+        return;
+    }
+
+    unregister_netdev(dev);
+    printk(KERN_INFO "Ethernet device unregistered\n");
+
+    free_netdev(dev);
+    printk(KERN_INFO "Ethernet device freed\n");
+}
+
+module_init(custom_init);
+module_exit(custom_exit);

shell.nix

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+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell rec {
+    buildInputs = with pkgs; [
+        linux.dev
+        gcc
+        wireshark 
+        gnumake
+    ];
+    shellHook = ''
+      export PATH="$PATH:$PWD/opt/bin"
+      export CC="i686-elf-gcc"
+      '';
+}