linux-kernel - Re: [PATCH v3 3/3] leds: trigger: implement a tty trigger

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Date:   Tue, 17 Dec 2019 17:23:13 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        Jiri Slaby <jslaby@...e.com>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 3/3] leds: trigger: implement a tty trigger

On Tue, Dec 17, 2019 at 04:27:24PM +0100, Greg Kroah-Hartman wrote:
> On Tue, Dec 17, 2019 at 04:07:36PM +0100, Uwe Kleine-König wrote:
> > Usage is as follows:
> > 
> > 	myled=ledname
> > 	tty=ttyS0
> > 
> > 	echo tty > /sys/class/leds/$myled/trigger
> > 	cat /sys/class/tty/$tty/dev > /sys/class/leds/$myled/dev
> 
> Is this the correct instructions?  Aren't you looking for a major/minor
> number instead in your sysfs file?

This is correct, yes, at least it works as intended on my machine.

/sys/class/tty/$tty/dev produces $major:$minor and that's what the
led-trigger consumes.

> > . When this new trigger is active it periodically checks the tty's
> > statistics and when it changed since the last check the led is flashed
> > once.
> > 
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > ---
> >  drivers/leds/trigger/Kconfig       |   7 ++
> >  drivers/leds/trigger/Makefile      |   1 +
> >  drivers/leds/trigger/ledtrig-tty.c | 159 +++++++++++++++++++++++++++++
> >  3 files changed, 167 insertions(+)
> >  create mode 100644 drivers/leds/trigger/ledtrig-tty.c
> > 
> > diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
> > index ce9429ca6dde..40ff08c93f56 100644
> > --- a/drivers/leds/trigger/Kconfig
> > +++ b/drivers/leds/trigger/Kconfig
> > @@ -144,4 +144,11 @@ config LEDS_TRIGGER_AUDIO
> >  	  the audio mute and mic-mute changes.
> >  	  If unsure, say N
> >  
> > +config LEDS_TRIGGER_TTY
> > +	tristate "LED Trigger for TTY devices"
> > +	depends on TTY
> > +	help
> > +	  This allows LEDs to be controlled by activity on ttys which includes
> > +	  serial devices like /dev/ttyS0.
> > +
> >  endif # LEDS_TRIGGERS
> > diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
> > index 733a83e2a718..25c4db97cdd4 100644
> > --- a/drivers/leds/trigger/Makefile
> > +++ b/drivers/leds/trigger/Makefile
> > @@ -15,3 +15,4 @@ obj-$(CONFIG_LEDS_TRIGGER_PANIC)	+= ledtrig-panic.o
> >  obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
> >  obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o
> >  obj-$(CONFIG_LEDS_TRIGGER_AUDIO)	+= ledtrig-audio.o
> > +obj-$(CONFIG_LEDS_TRIGGER_TTY)		+= ledtrig-tty.o
> > diff --git a/drivers/leds/trigger/ledtrig-tty.c b/drivers/leds/trigger/ledtrig-tty.c
> > new file mode 100644
> > index 000000000000..0157aa0b2ce3
> > --- /dev/null
> > +++ b/drivers/leds/trigger/ledtrig-tty.c
> > @@ -0,0 +1,159 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/leds.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/tty.h>
> > +#include <uapi/linux/serial.h>
> > +
> > +struct ledtrig_tty_data {
> > +	struct led_classdev *led_cdev;
> > +	struct delayed_work dwork;
> > +	struct tty_struct *tty;
> > +	dev_t device;
> > +	int rx, tx;
> > +};
> > +
> > +static void ledtrig_tty_halt(struct ledtrig_tty_data *trigger_data)
> > +{
> > +	cancel_delayed_work_sync(&trigger_data->dwork);
> > +}
> > +
> > +static void ledtrig_tty_restart(struct ledtrig_tty_data *trigger_data)
> > +{
> > +	if (!trigger_data->tty)
> > +		return;
> > +
> > +	schedule_delayed_work(&trigger_data->dwork, 0);
> > +}
> > +
> > +static ssize_t dev_show(struct device *dev,
> > +			struct device_attribute *attr, char *buf)
> > +{
> > +	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
> > +	ssize_t len = 0;
> > +
> > +	if (trigger_data->tty)
> > +		len = sprintf(buf, "%u\n", trigger_data->device);
> 
> Will that print a dev_t in a format that userspace can make sense of it?
> Should you split it up with MAJOR:MINOR instead?

Ah, yes, this needs fixing to match the format that is used in .store.

> > +
> > +	return len;
> > +}
> > +
> > +static ssize_t dev_store(struct device *dev,
> > +			 struct device_attribute *attr, const char *buf,
> > +			 size_t size)
> > +{
> > +	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
> > +	struct tty_struct *tty;
> > +	unsigned major, minor;
> > +	int ret;
> > +
> > +	if (size == 0 || (size == 1 && buf[0] == '\n')) {
> > +		tty = NULL;
> > +	} else {
> > +		ret = sscanf(buf, "%u:%u", &major, &minor);
> > +		if (ret < 2) {
> > +			dev_err(dev, "invalid value\n");
> 
> Can I DoS the syslog with this?  :)

Only if you can write to the sysfs file in which case you can DoS the
syslog anyhow :-)

> > +			return -EINVAL;
> > +		}
> > +
> > +		tty = tty_kopen_shared(MKDEV(major, minor));
> > +		if (IS_ERR(tty)) {
> > +			dev_err(dev, "failed to open tty: %pe\n", tty);
> 
> Same here, dev_dbg() perhaps?
> 
> Other than these minor things, looks good to me.
> 
> Your tty changes are fine, if I can get an ack from the led maintainers
> about a working patch 3, I'll be glad to take all 3 in my tree.

You'll get a v4 in a moment. Thanks for your prompt reviews.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |