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/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
  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 {
  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
  73 static 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
  91 static 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
 109 static 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
 115 static struct miscdevice xenbus_backend_dev = {
 116         .minor = MISC_DYNAMIC_MINOR,
 117         .name = "xen/xenbus_backend",
 118         .fops = &xenbus_backend_fops,
 119 };
 120
 121 static 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 }
 133 device_initcall(xenbus_backend_init);