Re: [PATCH v6 2/4] tty: rename tty_kopen() and add new function tty_kopen_shared()

[Johan Hovold <johan@kernel.org>]

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.

>  		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.

> + *
> + *	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.

Johan