I've been recently playing a bit with VirtualBox to debug my One live systems, and got a bit involved in VirtualBox packaging in the meantime. Our Mandriva package was missing the guest additions, so I added them recently (the packages are x11-driver-input-vboxmouse, x11-driver-video-vboxvideo, dkms-vboxadd, dkms-vboxvfs and virtualbox-guest-additions). They basically allow a better integration of mouse and X11 (clipboard) with the host, and to share files more easily, thanks to a vboxvfs module and a vboxfs mount helper.
But the vboxadd kernel module required some integration, since /dev/vboxadd was not created automatically. Upstream has an initscript to create it, but it's quite a weird trick to parse /proc/devices to get the major and create the device "a la main" with mknod.
A better solution is to make the kernel module send an uevent (with kobject_uevent()) when the device is registered in the kernel module, so that udev creates the device node automatically.
This can be done through the device_create() function (from drivers/base/core.c), but it requires a kernel class as argument, and we don't necessarily need to create one for vboxadd.
A simpler solution is to replace the original char device creation, register_chrdev() (from fs/char_dev.c), by using a misc character device. misc_register() (from drivers/char/misc.c) takes care of the character device registration and of sending the uevent to userspace.
#include <linux/miscdevice.h>
...
static struct miscdevice vbox_dev =
{
.minor = MISC_DYNAMIC_MINOR,
.name = "vboxadd",
.fops = &vbox_fops,
};
...
if (vbox_major > 0) {
err = register_chrdev(vbox_major, "vboxadd", &vbox_fops);
} else {
err = misc_register(&vbox_dev);
}
...
if (vbox_major > 0) {
unregister_chrdev(vbox_major, "vboxadd");
} else {
misc_deregister(&vbox_dev);
}
The final touch is to make the device node reachable by end-users, which is made easy since Mandriva uses pam_console. pam_console_apply is called for every device node created by udev, so we just need to add a rule to make vboxadd devices owned by the console user (i.e. the user physically logged on the system).
$ cat /etc/security/console.perms.d/60-vboxadd.perms <vboxadd>=/dev/vboxadd* <console> 0600 <vboxadd> 0600 root
