printer: perform probe on startup

This stops the printer driver from hanging the entire system when
/dev/lp is opened on systems that do not have a parallel port. With
this change, the printer driver shuts down immediately after loading
on such systems.

diff --git a/drivers/printer/printer.c b/drivers/printer/printer.c
index bb1374885ba13393bd76e8f50d08dbd91e788081..331d048282f8547109e762649eef11f74892f256 100644 (file)
--- a/drivers/printer/printer.c
+++ b/drivers/printer/printer.c
@@ -107,6 +107,7 @@ FORWARD _PROTOTYPE( void output_done, (void) );
 FORWARD _PROTOTYPE( void do_write, (message *m_ptr) );
 FORWARD _PROTOTYPE( void do_status, (message *m_ptr) );
 FORWARD _PROTOTYPE( void prepare_output, (void) );
+FORWARD _PROTOTYPE( int do_probe, (void) );
 FORWARD _PROTOTYPE( void do_initialize, (void) );
 FORWARD _PROTOTYPE( void reply, (int code,int replyee,int proc,int status));
 FORWARD _PROTOTYPE( void do_printer_output, (void) );
@@ -193,6 +194,11 @@ PRIVATE void sef_local_startup()
 PRIVATE int sef_cb_init_fresh(int UNUSED(type), sef_init_info_t *UNUSED(info))
 {
 /* Initialize the printer driver. */
+
+  /* If no printer is present, do not start. */
+  if (!do_probe())
+       return ENODEV;  /* arbitrary error code */
+
   /* Announce we are up! */
   chardriver_announce();
 
@@ -352,6 +358,23 @@ int status;                        /* number of  chars printed or error code */
   send(replyee, &pr_mess);             /* send the message */
 }
 
+/*===========================================================================*
+ *                             do_probe                                     *
+ *===========================================================================*/
+PRIVATE int do_probe(void)
+{
+/* See if there is a printer at all. */
+
+  /* Get the base port for first printer. */
+  if(sys_vircopy(SELF, BIOS_SEG, LPT1_IO_PORT_ADDR,
+       SELF, D, (vir_bytes) &port_base, LPT1_IO_PORT_SIZE) != OK) {
+       panic("do_initialize: sys_vircopy failed");
+  }
+
+  /* If the port is zero, the parallel port is not available at all. */
+  return (port_base != 0);
+}
+
 /*===========================================================================*
  *                             do_initialize                                *
  *===========================================================================*/
@@ -362,11 +385,6 @@ PRIVATE void do_initialize()
   if (initialized) return;
   initialized = TRUE;
   
-  /* Get the base port for first printer.  */
-  if(sys_vircopy(SELF, BIOS_SEG, LPT1_IO_PORT_ADDR, 
-       SELF, D, (vir_bytes) &port_base, LPT1_IO_PORT_SIZE) != OK) {
-       panic("do_initialize: sys_vircopy failed");
-  }
   if(sys_outb(port_base + 2, INIT_PRINTER) != OK) {
        printf("printer: sys_outb of %x failed\n", port_base+2);
        panic("do_initialize: sys_outb init failed");