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