drivers/xen/xenbus/xenbus_dev_backend.c

   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
  21 MODULE_LICENSE("GPL");
  22
  23 static 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
  31 static 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
  75 static 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
  93 static 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
 111 static 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
 117 static struct miscdevice xenbus_backend_dev = {
 118         .minor = MISC_DYNAMIC_MINOR,
 119         .name = "xen/xenbus_backend",
 120         .fops = &xenbus_backend_fops,
 121 };
 122
 123 static 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
 136 static void __exit xenbus_backend_exit(void)
 137 {
 138         misc_deregister(&xenbus_backend_dev);
 139 }
 140
 141 module_init(xenbus_backend_init);
 142 module_exit(xenbus_backend_exit);