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@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: linux-serial@xxxxxxxxxxxxxxx
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: kgdb-bugreport@xxxxxxxxxxxxxxxxxxxxx
---
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;
--
1.9.3
--
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