linux-kernel - Re: [PATCH v2 1/3] tty: new helper function tty_kopen

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Date:   Tue, 17 Dec 2019 09:27:33 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-serial@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v2 1/3] tty: new helper function tty_kopen_shared

On Tue, Dec 17, 2019 at 09:17:16AM +0100, Uwe Kleine-König wrote:
> This function gives a struct tty_struct for a given device number.

That says _what_ this does, but not why :)

> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
>  drivers/tty/tty_io.c | 27 +++++++++++++++++++++++++++
>  include/linux/tty.h  |  1 +
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index d9f54c7d94f2..584025117cd3 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1925,6 +1925,33 @@ struct tty_struct *tty_kopen(dev_t device)
>  }
>  EXPORT_SYMBOL_GPL(tty_kopen);
>  
> +/*
> + * Caller gets a reference on (non-error) ttys, that must be disposed using
> + * tty_kref_put().
> + */

It's a global function, can you please use kerneldoc?
And please describe it as well as tty_kopen() is.

> +struct tty_struct *tty_kopen_shared(dev_t device)
> +{
> +	struct tty_struct *tty;
> +	struct tty_driver *driver;
> +	int index = -1;
> +
> +	mutex_lock(&tty_mutex);
> +	driver = tty_lookup_driver(device, NULL, &index);
> +	if (IS_ERR(driver)) {
> +		tty = ERR_CAST(driver);
> +		goto err_lookup_driver;
> +	}
> +
> +	tty = tty_driver_lookup_tty(driver, NULL, index);

No error check?

> +
> +	tty_driver_kref_put(driver);
> +err_lookup_driver:
> +
> +	mutex_unlock(&tty_mutex);
> +	return tty;

Can't you share a lot of this code with tty_kopen()?  It feels odd to
duplicatate _almost_ all of it here.

> +}
> +EXPORT_SYMBOL(tty_kopen_shared);

EXPORT_SYMBOL_GPL() please.

thanks,

greg k-h