There is no in-kernel function to get the status register of a tty device
like the TIOCMGET ioctl returns to userspace. Create a new function,
tty_get_tiocm(), to obtain the status register that other portions of the
kernel can call if they need this information, and move the existing
internal tty_tiocmget() function to use this interface.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Florian Eckert <fe@dev.tdt.de>
---
 drivers/tty/tty_io.c | 28 ++++++++++++++++++++++------
 include/linux/tty.h  |  1 +
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 06414e43e0b5..e2e93404133e 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2498,6 +2498,24 @@ static int send_break(struct tty_struct *tty, unsigned int duration)
 	return retval;
 }
 
+/**
+ * tty_get_tiocm - get tiocm status register
+ * @tty: tty device
+ *
+ * Obtain the modem status bits from the tty driver if the feature
+ * is supported.
+ */
+int tty_get_tiocm(struct tty_struct *tty)
+{
+	int retval = -ENOTTY;
+
+	if (tty->ops->tiocmget)
+		retval = tty->ops->tiocmget(tty);
+
+	return retval;
+}
+EXPORT_SYMBOL_GPL(tty_get_tiocm);
+
 /**
  * tty_tiocmget - get modem status
  * @tty: tty device
@@ -2510,14 +2528,12 @@ static int send_break(struct tty_struct *tty, unsigned int duration)
  */
 static int tty_tiocmget(struct tty_struct *tty, int __user *p)
 {
-	int retval = -ENOTTY;
+	int retval;
 
-	if (tty->ops->tiocmget) {
-		retval = tty->ops->tiocmget(tty);
+	retval = tty_get_tiocm(tty);
+	if (retval >= 0)
+		retval = put_user(retval, p);
 
-		if (retval >= 0)
-			retval = put_user(retval, p);
-	}
 	return retval;
 }
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 4b6340ac2af2..d219a11e3fe0 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -419,6 +419,7 @@ bool tty_unthrottle_safe(struct tty_struct *tty);
 int tty_do_resize(struct tty_struct *tty, struct winsize *ws);
 int tty_get_icount(struct tty_struct *tty,
 		struct serial_icounter_struct *icount);
+int tty_get_tiocm(struct tty_struct *tty);
 int is_current_pgrp_orphaned(void);
 void tty_hangup(struct tty_struct *tty);
 void tty_vhangup(struct tty_struct *tty);
-- 
2.30.2

On 09. 11. 23, 9:50, Florian Eckert wrote:
> There is no in-kernel function to get the status register of a tty device
> like the TIOCMGET ioctl returns to userspace. Create a new function,
> tty_get_tiocm(), to obtain the status register that other portions of the
> kernel can call if they need this information, and move the existing
> internal tty_tiocmget() function to use this interface.
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Florian Eckert <fe@dev.tdt.de>
> ---
>   drivers/tty/tty_io.c | 28 ++++++++++++++++++++++------
>   include/linux/tty.h  |  1 +
>   2 files changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 06414e43e0b5..e2e93404133e 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -2498,6 +2498,24 @@ static int send_break(struct tty_struct *tty, unsigned int duration)
>   	return retval;
>   }
>   
> +/**
> + * tty_get_tiocm - get tiocm status register
> + * @tty: tty device
> + *
> + * Obtain the modem status bits from the tty driver if the feature
> + * is supported.
> + */
> +int tty_get_tiocm(struct tty_struct *tty)
> +{
> +	int retval = -ENOTTY;
> +
> +	if (tty->ops->tiocmget)
> +		retval = tty->ops->tiocmget(tty);
> +
> +	return retval;

Why not simply:
{
  if (tty->ops->tiocmget)
     return tty->ops->tiocmget(tty);

  return -ENOTTY;
}
?

thanks,
-- 
js
suse labs

On 2023-11-20 08:21, Jiri Slaby wrote:
> On 09. 11. 23, 9:50, Florian Eckert wrote:
>> There is no in-kernel function to get the status register of a tty 
>> device
>> like the TIOCMGET ioctl returns to userspace. Create a new function,
>> tty_get_tiocm(), to obtain the status register that other portions of 
>> the
>> kernel can call if they need this information, and move the existing
>> internal tty_tiocmget() function to use this interface.
>> 
>> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Signed-off-by: Florian Eckert <fe@dev.tdt.de>
>> ---
>>   drivers/tty/tty_io.c | 28 ++++++++++++++++++++++------
>>   include/linux/tty.h  |  1 +
>>   2 files changed, 23 insertions(+), 6 deletions(-)
>> 
>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
>> index 06414e43e0b5..e2e93404133e 100644
>> --- a/drivers/tty/tty_io.c
>> +++ b/drivers/tty/tty_io.c
>> @@ -2498,6 +2498,24 @@ static int send_break(struct tty_struct *tty, 
>> unsigned int duration)
>>   	return retval;
>>   }
>>   +/**
>> + * tty_get_tiocm - get tiocm status register
>> + * @tty: tty device
>> + *
>> + * Obtain the modem status bits from the tty driver if the feature
>> + * is supported.
>> + */
>> +int tty_get_tiocm(struct tty_struct *tty)
>> +{
>> +	int retval = -ENOTTY;
>> +
>> +	if (tty->ops->tiocmget)
>> +		retval = tty->ops->tiocmget(tty);
>> +
>> +	return retval;
> 
> Why not simply:

I just did it this way because it is also done this way in other 
functions
in this file.

> {
>  if (tty->ops->tiocmget)
>     return tty->ops->tiocmget(tty);
> 
>  return -ENOTTY;
> }

Of course, we could also do it this way. If this is the C style for the 
kernel,
then I will change it. Please give me a short feedback whether I should 
change it
and send a v9, or whether it is just a comment from you.

Best regards

Florian