linux-kernel - Re: [PATCH 01/10] gpiolib: provide gpiochip_dup_line

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Date:   Wed, 29 Nov 2023 16:57:22 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 01/10] gpiolib: provide gpiochip_dup_line_label()

On Wed, Nov 29, 2023 at 03:24:02PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> gpiochip_is_requested() not only has a misleading name but it returns
> a pointer to a string that is freed when the descriptor is released.
> 
> Provide a new helper meant to replace it, which returns a copy of the
> label string instead.

...

> +/**
> + * gpiochip_dup_line_label - Get a copy of the consumer label.
> + * @gc: GPIO chip controlling this line.
> + * @offset: Hardware offset of the line.
> + *
> + * Returns:
> + * Pointer to a copy of the consumer label if the line is requested or NULL
> + * if it's not. If a valid pointer was returned, it must be freed using
> + * kfree(). In case of a memory allocation error, the function returns %ENOMEM.

kfree_const() ? (see below)

> + * Must not be called from atomic context.
> + */
> +char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
> +{
> +	const char *label;
> +	char *cpy;

Why not "copy"?

> +
> +	label = gpiochip_is_requested(gc, offset);
> +	if (!label)
> +		return NULL;

> +	cpy = kstrdup(label, GFP_KERNEL);

You probably want to have kstrdup_const(). However, I haven't checked
if we have such use cases.

> +	if (!cpy)
> +		return ERR_PTR(-ENOMEM);
> +
> +	return cpy;
> +}

So, how does this differ from the previous one? You need to hold a reference
to the descriptor before copying and release it after.

-- 
With Best Regards,
Andy Shevchenko