Re: [PATCH 01/10] gpiolib: provide gpiochip_dup_line_label()

Andy Shevchenko
2023-11-29T14:57:32Z

On Wed, Nov 29, 2023 at 03:24:02PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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