Implement vm_enable_net API

The vm_enable_net function to facilitate the integration
of additional I/O devices in the future. The function initializes
the virtio-net device by setting up the tap device using virtio_net_init
and subsequently registers the virtio-net device with the PCI bus.
This function is invoked during the VM initialization session.

src/main.c

@@ -93,6 +93,8 @@ int main(int argc, char *argv[])
         return throw_err("Failed to load initrd");
     if (diskimg_file && vm_load_diskimg(&vm, diskimg_file) < 0)
         return throw_err("Failed to load disk image");
+    if (vm_enable_net(&vm) < 0)
+        return throw_err("Failed to Enable Virtio-Net Device");
 
     if (vm_late_init(&vm) < 0)
         return -1;

src/vm.c

@@ -97,6 +97,14 @@ int vm_load_diskimg(vm_t *v, const char *diskimg_file)
     return 0;
 }
 
+int vm_enable_net(vm_t *v)
+{
+    if (!virtio_net_init(&v->virtio_net_dev))
+        return -1;
+    virtio_net_init_pci(&v->virtio_net_dev, &v->pci, &v->io_bus, &v->mmio_bus);
+    return 0;
+}
+
 void vm_handle_io(vm_t *v, struct kvm_run *run)
 {
     uint64_t addr = run->io.port;

src/vm.h

@@ -31,6 +31,7 @@ int vm_load_image(vm_t *v, const char *image_path);
 int vm_load_initrd(vm_t *v, const char *initrd_path);
 int vm_load_diskimg(vm_t *v, const char *diskimg_file);
 int vm_late_init(vm_t *v);
+int vm_enable_net(vm_t *v);
 int vm_run(vm_t *v);
 int vm_irq_line(vm_t *v, int irq, int level);
 void *vm_guest_to_host(vm_t *v, uint64_t guest);