1#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  2
  3#include <linux/slab.h>
  4#include <linux/types.h>
  5#include <linux/mm.h>
  6#include <linux/fs.h>
  7#include <linux/miscdevice.h>
  8#include <linux/module.h>
  9#include <linux/capability.h>
 10
 11#include <xen/xen.h>
 12#include <xen/page.h>
 13#include <xen/xenbus.h>
 14#include <xen/xenbus_dev.h>
 15#include <xen/grant_table.h>
 16#include <xen/events.h>
 17#include <asm/xen/hypervisor.h>
 18
 19#include "xenbus_comms.h"
 20
 21MODULE_LICENSE("GPL");
 22
 23static int xenbus_backend_open(struct inode *inode, struct file *filp)
 24{
 25	if (!capable(CAP_SYS_ADMIN))
 26		return -EPERM;
 27
 28	return nonseekable_open(inode, filp);
 29}
 30
 31static long xenbus_alloc(domid_t domid)
 32{
 33	struct evtchn_alloc_unbound arg;
 34	int err = -EEXIST;
 35
 36	xs_suspend();
 37
 38	/* If xenstored_ready is nonzero, that means we have already talked to
 39	 * xenstore and set up watches. These watches will be restored by
 40	 * xs_resume, but that requires communication over the port established
 41	 * below that is not visible to anyone until the ioctl returns.
 42	 *
 43	 * This can be resolved by splitting the ioctl into two parts
 44	 * (postponing the resume until xenstored is active) but this is
 45	 * unnecessarily complex for the intended use where xenstored is only
 46	 * started once - so return -EEXIST if it's already running.
 47	 */
 48	if (xenstored_ready)
 49		goto out_err;
 50
 51	gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
 52			virt_to_mfn(xen_store_interface), 0 /* writable */);
 53
 54	arg.dom = DOMID_SELF;
 55	arg.remote_dom = domid;
 56
 57	err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
 58	if (err)
 59		goto out_err;
 60
 61	if (xen_store_evtchn > 0)
 62		xb_deinit_comms();
 63
 64	xen_store_evtchn = arg.port;
 65
 66	xs_resume();
 67
 68	return arg.port;
 69
 70 out_err:
 71	xs_suspend_cancel();
 72	return err;
 73}
 74
 75static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
 76				 unsigned long data)
 77{
 78	if (!capable(CAP_SYS_ADMIN))
 79		return -EPERM;
 80
 81	switch (cmd) {
 82	case IOCTL_XENBUS_BACKEND_EVTCHN:
 83		if (xen_store_evtchn > 0)
 84			return xen_store_evtchn;
 85		return -ENODEV;
 86	case IOCTL_XENBUS_BACKEND_SETUP:
 87		return xenbus_alloc(data);
 88	default:
 89		return -ENOTTY;
 90	}
 91}
 92
 93static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
 94{
 95	size_t size = vma->vm_end - vma->vm_start;
 96
 97	if (!capable(CAP_SYS_ADMIN))
 98		return -EPERM;
 99
100	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
101		return -EINVAL;
102
103	if (remap_pfn_range(vma, vma->vm_start,
104			    virt_to_pfn(xen_store_interface),
105			    size, vma->vm_page_prot))
106		return -EAGAIN;
107
108	return 0;
109}
110
111static const struct file_operations xenbus_backend_fops = {
112	.open = xenbus_backend_open,
113	.mmap = xenbus_backend_mmap,
114	.unlocked_ioctl = xenbus_backend_ioctl,
115};
116
117static struct miscdevice xenbus_backend_dev = {
118	.minor = MISC_DYNAMIC_MINOR,
119	.name = "xen/xenbus_backend",
120	.fops = &xenbus_backend_fops,
121};
122
123static int __init xenbus_backend_init(void)
124{
125	int err;
126
127	if (!xen_initial_domain())
128		return -ENODEV;
129
130	err = misc_register(&xenbus_backend_dev);
131	if (err)
132		pr_err("Could not register xenbus backend device\n");
133	return err;
134}
135
136static void __exit xenbus_backend_exit(void)
137{
138	misc_deregister(&xenbus_backend_dev);
139}
140
141module_init(xenbus_backend_init);
142module_exit(xenbus_backend_exit);