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Subject[PATCH] Only initialize hvc_console if needed, cleanup Kconfig help
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On Thu, 2007-08-16 at 16:16 -0400, Dave Jones wrote:
> asides from the needed Kconfig clarification, is it necessary for khvcd
> to run at all if the lguest module hasn't been loaded ? Is it possible
> we can somehow delay creation of the kthread ?

It's for lguest guests, so it kind of needs to be built-in. But yes, it
should be made to suck less. Xen will want it too.

How's this?
==
This changes hvc_init() to be called only when someone actually uses
the hvc_console driver.

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>

diff -r 0730da2377be drivers/char/Kconfig
--- a/drivers/char/Kconfig Tue Aug 14 12:46:08 2007 +1000
+++ b/drivers/char/Kconfig Fri Aug 17 09:05:12 2007 +1000
@@ -568,10 +568,10 @@ config HVC_DRIVER
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.
- It will automatically be selected if one of the back-end console drivers
- is selected.
+ Generic "hypervisor virtual console" infrastructure for various
+ hypervisors (pSeries, Xen, lguest).
+ It will automatically be selected if one of those back-end
+ console drivers is selected.


config HVC_CONSOLE
diff -r 0730da2377be drivers/char/hvc_console.c
--- a/drivers/char/hvc_console.c Tue Aug 14 12:46:08 2007 +1000
+++ b/drivers/char/hvc_console.c Fri Aug 17 09:15:24 2007 +1000
@@ -68,6 +68,8 @@ 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;
@@ -754,6 +756,13 @@ struct hvc_struct __devinit *hvc_alloc(u
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_stru
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;
- }
-
- if (tty_register_driver(drv))
- panic("Couldn't register hvc console driver\n");
-
+ printk(KERN_ERR "Couldn't create kthread for console.\n");
+ err = PTR_ERR(hvc_task);
+ goto put_tty;
+ }
+
+ 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;
-}
-module_init(hvc_init);
+
+put_tty:
+ put_tty_driver(hvc_driver);
+stop_thread:
+ kthread_stop(hvc_task);
+ hvc_task = NULL;
+out:
+ return err;
+}

/* 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);
-
- tty_unregister_driver(hvc_driver);
- /* return tty_struct instances allocated in hvc_init(). */
- put_tty_driver(hvc_driver);
- unregister_console(&hvc_con_driver);
+ 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);
+ }
}
module_exit(hvc_exit);





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