xenbus_dev_backend.c revision b8b0f559c7b1dcf5503817e518c81c9a18ee45e0 
1#include <linux/slab.h>
2#include <linux/types.h>
3#include <linux/mm.h>
4#include <linux/fs.h>
5#include <linux/miscdevice.h>
6#include <linux/module.h>
7#include <linux/capability.h>
8
9#include <xen/xen.h>
10#include <xen/page.h>
11#include <xen/xenbus.h>
12#include <xen/xenbus_dev.h>
13#include <xen/grant_table.h>
14#include <xen/events.h>
15#include <asm/xen/hypervisor.h>
16
17#include "xenbus_comms.h"
18
19MODULE_LICENSE("GPL");
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_mfn(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, unsigned long data)
74{
75	if (!capable(CAP_SYS_ADMIN))
76		return -EPERM;
77
78	switch (cmd) {
79		case IOCTL_XENBUS_BACKEND_EVTCHN:
80			if (xen_store_evtchn > 0)
81				return xen_store_evtchn;
82			return -ENODEV;
83
84		case IOCTL_XENBUS_BACKEND_SETUP:
85			return xenbus_alloc(data);
86
87		default:
88			return -ENOTTY;
89	}
90}
91
92static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
93{
94	size_t size = vma->vm_end - vma->vm_start;
95
96	if (!capable(CAP_SYS_ADMIN))
97		return -EPERM;
98
99	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
100		return -EINVAL;
101
102	if (remap_pfn_range(vma, vma->vm_start,
103			    virt_to_pfn(xen_store_interface),
104			    size, vma->vm_page_prot))
105		return -EAGAIN;
106
107	return 0;
108}
109
110static const struct file_operations xenbus_backend_fops = {
111	.open = xenbus_backend_open,
112	.mmap = xenbus_backend_mmap,
113	.unlocked_ioctl = xenbus_backend_ioctl,
114};
115
116static struct miscdevice xenbus_backend_dev = {
117	.minor = MISC_DYNAMIC_MINOR,
118	.name = "xen/xenbus_backend",
119	.fops = &xenbus_backend_fops,
120};
121
122static int __init xenbus_backend_init(void)
123{
124	int err;
125
126	if (!xen_initial_domain())
127		return -ENODEV;
128
129	err = misc_register(&xenbus_backend_dev);
130	if (err)
131		printk(KERN_ERR "Could not register xenbus backend device\n");
132	return err;
133}
134
135static void __exit xenbus_backend_exit(void)
136{
137	misc_deregister(&xenbus_backend_dev);
138}
139
140module_init(xenbus_backend_init);
141module_exit(xenbus_backend_exit);
142