Linux Kernel  3.7.1
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xenbus_dev_backend.c
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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 
19 MODULE_LICENSE("GPL");
20 
21 static 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 
29 static long xenbus_alloc(domid_t domid)
30 {
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 
50  virt_to_mfn(xen_store_interface), 0 /* writable */);
51 
52  arg.dom = DOMID_SELF;
53  arg.remote_dom = domid;
54 
56  if (err)
57  goto out_err;
58 
59  if (xen_store_evtchn > 0)
61 
62  xen_store_evtchn = arg.port;
63 
64  xs_resume();
65 
66  return arg.port;
67 
68  out_err:
70  return err;
71 }
72 
73 static 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) {
80  if (xen_store_evtchn > 0)
81  return xen_store_evtchn;
82  return -ENODEV;
83 
85  return xenbus_alloc(data);
86 
87  default:
88  return -ENOTTY;
89  }
90 }
91 
92 static 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,
104  size, vma->vm_page_prot))
105  return -EAGAIN;
106 
107  return 0;
108 }
109 
110 static 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 
116 static struct miscdevice xenbus_backend_dev = {
117  .minor = MISC_DYNAMIC_MINOR,
118  .name = "xen/xenbus_backend",
119  .fops = &xenbus_backend_fops,
120 };
121 
122 static 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 
135 static void __exit xenbus_backend_exit(void)
136 {
137  misc_deregister(&xenbus_backend_dev);
138 }
139 
140 module_init(xenbus_backend_init);
141 module_exit(xenbus_backend_exit);