vt: add an activate and lock

X and other graphical interfaces need to be able to flip to a console
and lock it into graphics mode without races.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 37 insertions, 1 deletions

diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index d29fbd44bdca..0fceb8f4d6f2 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -972,6 +972,41 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                 }
                 break;
 
+        case VT_SETACTIVATE:
+        {
+                struct vt_setactivate vsa;
+
+                if (!perm)
+                        goto eperm;
+
+                if (copy_from_user(&vsa, (struct vt_setactivate __user *)arg,
+                                                sizeof(struct vt_setactivate)))
+                        return -EFAULT;
+                if (vsa.console == 0 || vsa.console > MAX_NR_CONSOLES)
+                        ret = -ENXIO;
+                else {
+                        vsa.console--;
+                        acquire_console_sem();
+                        ret = vc_allocate(vsa.console);
+                        if (ret == 0) {
+                                struct vc_data *nvc;
+                                /* This is safe providing we don't drop the
+                                   console sem between vc_allocate and
+                                   finishing referencing nvc */
+                                nvc = vc_cons[vsa.console].d;
+                                nvc->vt_mode = vsa.mode;
+                                nvc->vt_mode.frsig = 0;
+                                put_pid(nvc->vt_pid);
+                                nvc->vt_pid = get_pid(task_pid(current));
+                        }
+                        release_console_sem();
+                        if (ret)
+                                break;
+                        /* Commence switch and lock */
+                        set_console(arg);
+                }
+        }
+
         /*
          * wait until the specified VT has been activated
          */
@@ -1342,7 +1377,8 @@ void vc_SAK(struct work_struct *work)
 }
 
 /*
- * Performs the back end of a vt switch
+ * Performs the back end of a vt switch. Called under the console
+ * semaphore.
  */
 static void complete_change_console(struct vc_data *vc)
 {