On Fri, Jul 11, 2014 at 01:30:11PM +0100, Daniel Thompson wrote:

At present it is not possible to boot with the ttyNMI0 console treating character input normally. To use the console 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).

Introducing a module parameter makes the console much more usable.

Signed-off-by: Daniel Thompson daniel.thompson@linaro.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.cz Cc: linux-serial@vger.kernel.org

---

drivers/tty/serial/kgdb_nmi.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c index cfadf29..9361d69 100644 --- a/drivers/tty/serial/kgdb_nmi.c +++ b/drivers/tty/serial/kgdb_nmi.c @@ -43,6 +43,11 @@ 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; +module_param_named(tty, kgdb_nmi_tty_enabled, bool, 0600); +MODULE_PARM_DESC(tty, "if set to false (default), characters received from "

•       "the UART will be passed exclusively to the knock "
  

•       "detector; when set to true characters will be passed "
  

•       "both to the knock detector and to the TTY layer");
  

Module options suck rocks through straws.

Isn't there _any_ other way to determine this "dynamically"? How will someone know to set this option?

Yeah, there are other options in this module, but please, why add more?

greg k-h

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: Daniel Thompson daniel.thompson@linaro.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.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 --- drivers/tty/serial/kgdb_nmi.c | 36 +++++++++++++++--------------------- 1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c index cfadf29..6ec7501 100644 --- a/drivers/tty/serial/kgdb_nmi.c +++ b/drivers/tty/serial/kgdb_nmi.c @@ -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;