Delay creation of khcvd thread

This changes hvc_init() to be called only when someone actually uses the
hvc_console driver.  Dave Jones complained when profiling bootup.

hvc_console used to only be for Power aka pSeries: now lguest and Xen both
want it built-in in case the kernel is a guest under one of those, even
though usually it will be a native boot.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 1232ace097e167989fd4b958dec491cee3534c55..57b801716fbe3229a3f8572f6880bacd24ed0d65 100644 (file)
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -585,8 +585,8 @@ config TIPAR
 config HVC_DRIVER
        bool
        help
-         Users of pSeries machines that want to utilize the hvc console front-end
-         module for their backend console driver should select this option.
+         Generic "hypervisor virtual console" infrastructure for various
+         hypervisors (pSeries, Xen, lguest).
          It will automatically be selected if one of the back-end console drivers
          is selected.
 

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 83c1151ec7a21559257f3663a59d0f59e4d92abc..8252f86685385f341aa6f34797d52581264ed543 100644 (file)
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -69,6 +69,8 @@ static struct task_struct *hvc_task;
 /* Picks up late kicks after list walk but before schedule() */
 static int hvc_kicked;
 
+static int hvc_init(void);
+
 #ifdef CONFIG_MAGIC_SYSRQ
 static int sysrq_pressed;
 #endif
@@ -754,6 +756,13 @@ struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int irq,
        struct hvc_struct *hp;
        int i;
 
+       /* We wait until a driver actually comes along */
+       if (!hvc_driver) {
+               int err = hvc_init();
+               if (err)
+                       return ERR_PTR(err);
+       }
+
        hp = kmalloc(ALIGN(sizeof(*hp), sizeof(long)) + outbuf_size,
                        GFP_KERNEL);
        if (!hp)
@@ -829,16 +838,18 @@ int __devexit hvc_remove(struct hvc_struct *hp)
        return 0;
 }
 
-/* Driver initialization.  Follow console initialization.  This is where the TTY
- * interfaces start to become available. */
-static int __init hvc_init(void)
+/* Driver initialization: called as soon as someone uses hvc_alloc(). */
+static int hvc_init(void)
 {
        struct tty_driver *drv;
+       int err;
 
        /* We need more than hvc_count adapters due to hotplug additions. */
        drv = alloc_tty_driver(HVC_ALLOC_TTY_ADAPTERS);
-       if (!drv)
-               return -ENOMEM;
+       if (!drv) {
+               err = -ENOMEM;
+               goto out;
+       }
 
        drv->owner = THIS_MODULE;
        drv->driver_name = "hvc";
@@ -854,30 +865,43 @@ static int __init hvc_init(void)
         * added later. */
        hvc_task = kthread_run(khvcd, NULL, "khvcd");
        if (IS_ERR(hvc_task)) {
-               panic("Couldn't create kthread for console.\n");
-               put_tty_driver(drv);
-               return -EIO;
+               printk(KERN_ERR "Couldn't create kthread for console.\n");
+               err = PTR_ERR(hvc_task);
+               goto put_tty;
        }
 
-       if (tty_register_driver(drv))
-               panic("Couldn't register hvc console driver\n");
+       err = tty_register_driver(drv);
+       if (err) {
+               printk(KERN_ERR "Couldn't register hvc console driver\n");
+               goto stop_thread;
+       }
 
+       /* FIXME: This mb() seems completely random.  Remove it. */
        mb();
        hvc_driver = drv;
        return 0;
+
+put_tty:
+       put_tty_driver(hvc_driver);
+stop_thread:
+       kthread_stop(hvc_task);
+       hvc_task = NULL;
+out:
+       return err;
 }
-module_init(hvc_init);
 
 /* This isn't particularly necessary due to this being a console driver
  * but it is nice to be thorough.
  */
 static void __exit hvc_exit(void)
 {
-       kthread_stop(hvc_task);
+       if (hvc_driver) {
+               kthread_stop(hvc_task);
 
-       tty_unregister_driver(hvc_driver);
-       /* return tty_struct instances allocated in hvc_init(). */
-       put_tty_driver(hvc_driver);
-       unregister_console(&hvc_con_driver);
+               tty_unregister_driver(hvc_driver);
+               /* return tty_struct instances allocated in hvc_init(). */
+               put_tty_driver(hvc_driver);
+               unregister_console(&hvc_con_driver);
+       }
 }
 module_exit(hvc_exit);