src/console_switch.c

   1 /* console_switch.c -- console grabbing routines for vlock,
   2  *                     the VT locking program for linux
   3  *
   4  * This program is copyright (C) 2007 Frank Benkstein, and is free
   5  * software which is freely distributable under the terms of the
   6  * GNU General Public License version 2, included as the file COPYING in this
   7  * distribution.  It is NOT public domain software, and any
   8  * redistribution not permitted by the GNU General Public License is
   9  * expressly forbidden without prior written permission from
  10  * the author.
  11  *
  12  */
  13
  14 #if !defined(__FreeBSD__) && !defined(_GNU_SOURCE)
  15 #define _GNU_SOURCE
  16 #endif
  17
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <unistd.h>
  22 #include <fcntl.h>
  23 #include <sys/ioctl.h>
  24 #include <errno.h>
  25 #include <signal.h>
  26
  27 #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
  28 #include <sys/consio.h>
  29 #else
  30 #include <sys/vt.h>
  31 #endif
  32
  33 #include "console_switch.h"
  34
  35 /* Is console switching currently disabled? */
  36 bool console_switch_locked = false;
  37
  38 /* This handler is called whenever a user tries to
  39  * switch away from this virtual console. */
  40 static void release_vt(int __attribute__ ((__unused__)) signum)
  41 {
  42   /* Deny console switch. */
  43   (void) ioctl(STDIN_FILENO, VT_RELDISP, 0);
  44 }
  45
  46 /* This handler is called whenever a user switches to this
  47  * virtual console. */
  48 static void acquire_vt(int __attribute__ ((__unused__)) signum)
  49 {
  50   /* Acknowledge console switch. */
  51   (void) ioctl(STDIN_FILENO, VT_RELDISP, VT_ACKACQ);
  52 }
  53
  54 /* Console mode before switching was disabled. */
  55 static struct vt_mode vtm;
  56 /* Signal actions before console handling was disabled. */
  57 static struct sigaction sa_usr1;
  58 static struct sigaction sa_usr2;
  59
  60 /* Disable virtual console switching in the kernel.  If disabling fails false
  61  * is returned and *error is set to a diagnostic message that must be freed by
  62  * the caller.  */
  63 bool lock_console_switch(char **error)
  64 {
  65   /* Console mode when switching is disabled. */
  66   struct vt_mode lock_vtm;
  67   struct sigaction sa;
  68
  69   /* Get the virtual console mode. */
  70   if (ioctl(STDIN_FILENO, VT_GETMODE, &vtm) < 0) {
  71     if (errno == ENOTTY || errno == EINVAL)
  72       *error = strdup("this terminal is not a virtual console");
  73     else
  74       (void) asprintf(error, "could not get virtual console mode: %s", strerror(errno));
  75
  76     return false;
  77   }
  78
  79   /* Copy the current virtual console mode. */
  80   lock_vtm = vtm;
  81
  82   (void) sigemptyset(&(sa.sa_mask));
  83   sa.sa_flags = SA_RESTART;
  84   sa.sa_handler = release_vt;
  85   (void) sigaction(SIGUSR1, &sa, &sa_usr1);
  86   sa.sa_handler = acquire_vt;
  87   (void) sigaction(SIGUSR2, &sa, &sa_usr2);
  88
  89   /* Set terminal switching to be process governed. */
  90   lock_vtm.mode = VT_PROCESS;
  91   /* Set terminal release signal, i.e. sent when switching away. */
  92   lock_vtm.relsig = SIGUSR1;
  93   /* Set terminal acquire signal, i.e. sent when switching here. */
  94   lock_vtm.acqsig = SIGUSR2;
  95   /* Set terminal free signal, not implemented on either FreeBSD or Linux. */
  96   /* Linux ignores this but FreeBSD wants a valid signal number here. */
  97   lock_vtm.frsig = SIGHUP;
  98
  99   /* Set virtual console mode to be process governed thus disabling console
 100    * switching through the signal handlers above. */
 101   if (ioctl(STDIN_FILENO, VT_SETMODE, &lock_vtm) < 0) {
 102     (void) asprintf(error, "could not set virtual console mode: %s", strerror(errno));
 103     (void) sigaction(SIGUSR1, &sa_usr1, NULL);
 104     (void) sigaction(SIGUSR2, &sa_usr2, NULL);
 105     return false;
 106   }
 107
 108   console_switch_locked = true;
 109   return true;
 110 }
 111
 112 /* Reenable console switching if it was previously disabled. */
 113 void unlock_console_switch(void)
 114 {
 115   /* Restore virtual console mode. */
 116   if (console_switch_locked) {
 117     console_switch_locked = (ioctl(STDIN_FILENO, VT_SETMODE, &vtm) < 0);
 118
 119     if (console_switch_locked) {
 120       perror("could not restore virtual console mode");
 121     } else {
 122       (void) sigaction(SIGUSR1, &sa_usr1, NULL);
 123       (void) sigaction(SIGUSR2, &sa_usr2, NULL);
 124     }
 125   }
 126 }