1. 根目录:
2. drivers
3. xen
4. xenbus
5. xenbus_dev_backend.c

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/capability.h>

#include <xen/xen.h>
#include <xen/page.h>
#include <xen/xenbus_dev.h>

#include "xenbus_comms.h"

MODULE_LICENSE("GPL");

static int xenbus_backend_open(struct inode *inode, struct file *filp)
{
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	return nonseekable_open(inode, filp);
}

static long xenbus_backend_ioctl(struct file *file, unsigned int cmd, unsigned long data)
{
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	switch (cmd) {
		case IOCTL_XENBUS_BACKEND_EVTCHN:
			if (xen_store_evtchn > 0)
				return xen_store_evtchn;
			return -ENODEV;

		default:
			return -ENOTTY;
	}
}

static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
{
	size_t size = vma->vm_end - vma->vm_start;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
		return -EINVAL;

	if (remap_pfn_range(vma, vma->vm_start,
			    virt_to_pfn(xen_store_interface),
			    size, vma->vm_page_prot))
		return -EAGAIN;

	return 0;
}

const struct file_operations xenbus_backend_fops = {
	.open = xenbus_backend_open,
	.mmap = xenbus_backend_mmap,
	.unlocked_ioctl = xenbus_backend_ioctl,
};

static struct miscdevice xenbus_backend_dev = {
	.minor = MISC_DYNAMIC_MINOR,
	.name = "xen/xenbus_backend",
	.fops = &xenbus_backend_fops,
};

static int __init xenbus_backend_init(void)
{
	int err;

	if (!xen_initial_domain())
		return -ENODEV;

	err = misc_register(&xenbus_backend_dev);
	if (err)
		printk(KERN_ERR "Could not register xenbus backend device\n");
	return err;
}

static void __exit xenbus_backend_exit(void)
{
	misc_deregister(&xenbus_backend_dev);
}

module_init(xenbus_backend_init);
module_exit(xenbus_backend_exit);