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From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Johan Hovold <johan@kernel.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>,
	Pavel Machek <pavel@ucw.cz>, Dan Murphy <dmurphy@ti.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel@pengutronix.de, linux-serial@vger.kernel.org
Subject: Re: [PATCH v6 2/4] tty: rename tty_kopen() and add new function tty_kopen_shared()
Date: Wed, 19 Feb 2020 17:37:58 +0100
Message-ID: <20200219163758.5rypsol4n6ucost4@pengutronix.de> (raw)
In-Reply-To: <20200219132113.GD32540@localhost>

On Wed, Feb 19, 2020 at 02:21:13PM +0100, Johan Hovold wrote:
> On Thu, Feb 13, 2020 at 10:15:58AM +0100, Uwe Kleine-König wrote:
> > From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > 
> > Introduce a new function tty_kopen_shared() that yields a struct
> > tty_struct. The semantic difference to tty_kopen() is that the tty is
> > expected to be used already. So rename tty_kopen() to
> > tty_kopen_exclusive() for clearness, adapt the single user and put the
> > common code in a new static helper function.
> > 
> > tty_kopen_shared is to be used to implement an LED trigger for tty
> > devices in one of the next patches.
> > 
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > ---
>  
> > -/**
> > - *	tty_kopen	-	open a tty device for kernel
> > - *	@device: dev_t of device to open
> > - *
> > - *	Opens tty exclusively for kernel. Performs the driver lookup,
> > - *	makes sure it's not already opened and performs the first-time
> > - *	tty initialization.
> > - *
> > - *	Returns the locked initialized &tty_struct
> > - *
> > - *	Claims the global tty_mutex to serialize:
> > - *	  - concurrent first-time tty initialization
> > - *	  - concurrent tty driver removal w/ lookup
> > - *	  - concurrent tty removal from driver table
> > - */
> > -struct tty_struct *tty_kopen(dev_t device)
> > +static struct tty_struct *tty_kopen(dev_t device, int shared)
> >  {
> >  	struct tty_struct *tty;
> >  	struct tty_driver *driver;
> > @@ -1905,7 +1890,7 @@ struct tty_struct *tty_kopen(dev_t device)
> >  
> >  	/* check whether we're reopening an existing tty */
> >  	tty = tty_driver_lookup_tty(driver, NULL, index);
> > -	if (IS_ERR(tty))
> > +	if (IS_ERR(tty) || shared)
> 
> So here you skip initialisation and return NULL if the tty isn't already
> in use (e.g. is open) when shared is set.

Which is good, right? If I remember my tests correctly this even works
if the tty isn't opened but just "exists".

> >  		goto out;
> >  
> >  	if (tty) {
> > @@ -1923,7 +1908,44 @@ struct tty_struct *tty_kopen(dev_t device)
> >  	tty_driver_kref_put(driver);
> >  	return tty;
> >  }
> > -EXPORT_SYMBOL_GPL(tty_kopen);
> > +
> > +/**
> > + *	tty_kopen_exclusive	-	open a tty device for kernel
> > + *	@device: dev_t of device to open
> > + *
> > + *	Opens tty exclusively for kernel. Performs the driver lookup,
> > + *	makes sure it's not already opened and performs the first-time
> > + *	tty initialization.
> > + *
> > + *	Returns the locked initialized &tty_struct
> > + *
> > + *	Claims the global tty_mutex to serialize:
> > + *	  - concurrent first-time tty initialization
> > + *	  - concurrent tty driver removal w/ lookup
> > + *	  - concurrent tty removal from driver table
> > + */
> > +struct tty_struct *tty_kopen_exclusive(dev_t device)
> > +{
> > +	return tty_kopen(device, 0);
> > +}
> > +EXPORT_SYMBOL_GPL(tty_kopen_exclusive);
> > +
> > +/**
> > + *	tty_kopen_shared	-	open a tty device for shared in-kernel use
> > + *	@device: dev_t of device to open
> > + *
> > + *	Opens an already existing tty
> > + *	rnel. Performs the driver lookup,
> 
> "rnel"?
> 
> > + *	makes sure it's not already opened and performs the first-time
> > + *	tty initialization.
> 
> Yet, you claim to do initialisation here, which isn't the case.

Yeah, wrong (and incomplete) copy of the tty_kopen_exclusive docstring.

> > + *
> > + *	Locking is identical to tty_kopen() above.
> > + */
> > +struct tty_struct *tty_kopen_shared(dev_t device)
> > +{
> > +	return tty_kopen(device, 1);
> > +}
> > +EXPORT_SYMBOL_GPL(tty_kopen_shared);
> 
> This "kopen" naming is unfortunate as the tty isn't really opened by
> either of these functions, but that's not something you introduced.

Ack, will send a v7 with the doc string fixed.

Thanks for taking the time to look over 
Uwe

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

  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  9:15 [PATCH v6 0/4] leds: trigger: implement a tty trigger Uwe Kleine-König
2020-02-13  9:15 ` [PATCH v6 1/4] lib: new helper kstrtodev_t() Uwe Kleine-König
2020-02-19 19:50   ` Andy Shevchenko
2020-02-20  7:49     ` Uwe Kleine-König
2020-02-20 10:22       ` Andy Shevchenko
2020-02-20 10:57         ` Uwe Kleine-König
2020-02-20 11:46           ` Andy Shevchenko
2020-02-20 11:57             ` Andy Shevchenko
2020-02-20 14:01             ` Uwe Kleine-König
2020-02-21  8:42               ` Andy Shevchenko
2020-02-21 10:53                 ` Uwe Kleine-König
2020-02-13  9:15 ` [PATCH v6 2/4] tty: rename tty_kopen() and add new function tty_kopen_shared() Uwe Kleine-König
2020-02-19 13:21   ` Johan Hovold
2020-02-19 16:37     ` Uwe Kleine-König [this message]
2020-02-19 17:17       ` Johan Hovold
2020-02-20 11:04         ` Uwe Kleine-König
2020-02-25  8:55           ` Johan Hovold
2020-02-25  9:05             ` Uwe Kleine-König
2020-02-13  9:15 ` [PATCH v6 3/4] tty: new helper function tty_get_icount() Uwe Kleine-König
2020-02-13  9:16 ` [PATCH v6 4/4] leds: trigger: implement a tty trigger Uwe Kleine-König
2020-02-19 10:52   ` Johan Hovold
2020-02-19 11:03     ` Uwe Kleine-König
2020-02-19 11:19       ` Johan Hovold
2020-02-19 12:48         ` Johan Hovold
2020-02-19 10:40 ` [PATCH v6 0/4] " Greg Kroah-Hartman
2020-02-26 14:02   ` Pavel Machek

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