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Commit c8b29f04 authored by Daniel Thompson's avatar Daniel Thompson Committed by Greg Kroah-Hartman
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tty: kgdb_nmi: Automatically manage tty enable 



At present it is not possible to boot with the ttyNMI0 console treating
character input normally, instead character input triggers a prompt
telling the user how to trigger the knock detector and enter the
debugger. To use the console normally requires that kdb be entered and
the nmi_console command be used to enable the console (or if only kgdb
is present then gdb must directly manipulate the value of
kgdb_nmi_tty_enabled).

This patch automates the management of kgdb_nmi_tty_enabled by keeping
track of the number of file handles that are open for reading and using
that to determine how to tty should operate.

The approach means that:

1. Behaviour before init starts is unchanged.

2. If the userspace runs a getty or some other interactive process on
   /dev/console (or explicitly on /dev/ttyNMI0) the tty will treat
   character input like any other tty.

3. If the userspace doesn't use /dev/console or if it uses /dev/console
   only to log messages (O_WRONLY) then the user prompt is retained.

Signed-off-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: kgdb-bugreport@lists.sourceforge.net
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3d1c90d4

drivers/tty/serial/kgdb_nmi.c

+15 −21
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ static char *kgdb_nmi_magic = "$3#33"; 
module_param_named(magic, kgdb_nmi_magic, charp, 0600);

MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");



static bool kgdb_nmi_tty_enabled;

static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0);



static int kgdb_nmi_console_setup(struct console *co, char *options)

{
@@ -136,7 +136,7 @@ static int kgdb_nmi_poll_one_knock(void) 
		n = 0;

	}



	if (kgdb_nmi_tty_enabled) {

	if (atomic_read(&kgdb_nmi_num_readers)) {

		kgdb_tty_recv(c);

		return 0;

	}
@@ -197,7 +197,8 @@ static void kgdb_nmi_tty_receiver(unsigned long data) 
	priv->timer.expires = jiffies + (HZ/100);

	add_timer(&priv->timer);



	if (likely(!kgdb_nmi_tty_enabled || !kfifo_len(&priv->fifo)))

	if (likely(!atomic_read(&kgdb_nmi_num_readers) ||

		   !kfifo_len(&priv->fifo)))

		return;



	while (kfifo_out(&priv->fifo, &ch, 1))
@@ -270,13 +271,23 @@ static void kgdb_nmi_tty_cleanup(struct tty_struct *tty) 
static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)

{

	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

	unsigned int mode = file->f_flags & O_ACCMODE;

	int ret;



	ret = tty_port_open(&priv->port, tty, file);

	if (!ret && (mode == O_RDONLY || mode == O_RDWR))

		atomic_inc(&kgdb_nmi_num_readers);



	return tty_port_open(&priv->port, tty, file);

	return ret;

}



static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)

{

	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

	unsigned int mode = file->f_flags & O_ACCMODE;



	if (mode == O_RDONLY || mode == O_RDWR)

		atomic_dec(&kgdb_nmi_num_readers);



	tty_port_close(&priv->port, tty, file);

}
@@ -313,12 +324,6 @@ static const struct tty_operations kgdb_nmi_tty_ops = { 
	.write		= kgdb_nmi_tty_write,

};



static int kgdb_nmi_enable_console(int argc, const char *argv[])

{

	kgdb_nmi_tty_enabled = !(argc == 1 && !strcmp(argv[1], "off"));

	return 0;

}



int kgdb_register_nmi_console(void)

{

	int ret;
@@ -348,19 +353,10 @@ int kgdb_register_nmi_console(void) 
		goto err_drv_reg;

	}



	ret = kdb_register("nmi_console", kgdb_nmi_enable_console, "[off]",

			   "switch to Linux NMI console", 0);

	if (ret) {

		pr_err("%s: can't register kdb command: %d\n", __func__, ret);

		goto err_kdb_reg;

	}



	register_console(&kgdb_nmi_console);

	arch_kgdb_ops.enable_nmi(1);



	return 0;

err_kdb_reg:

	tty_unregister_driver(kgdb_nmi_tty_driver);

err_drv_reg:

	put_tty_driver(kgdb_nmi_tty_driver);

	return ret;
@@ -375,8 +371,6 @@ int kgdb_unregister_nmi_console(void) 
		return 0;

	arch_kgdb_ops.enable_nmi(0);



	kdb_unregister("nmi_console");



	ret = unregister_console(&kgdb_nmi_console);

	if (ret)

		return ret;