linux-kernel - Re: [PATCH v1 1/4] iio: acpi: Fill data with NULL when iio_get_acpi_device_name_and

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Message-ID: <20241031191717.1a521f03@jic23-huawei>
Date: Thu, 31 Oct 2024 19:17:17 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Hans de Goede
 <hdegoede@...hat.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>, Dan
 Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v1 1/4] iio: acpi: Fill data with NULL when
 iio_get_acpi_device_name_and_data() fails

On Wed, 30 Oct 2024 18:02:17 +0200
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> Fill data with NULL, if provided, when returning NULL from
> iio_get_acpi_device_name_and_data(). Note, the current users check
> for name to be valid, except one case which was initially doing
> like that and has to be fixed separately.
> 
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Closes: https://lore.kernel.org/r/54fac4a7-b601-40ce-8c00-d94807f5e214@stanley.mountain
> Fixes: dc60de4eb0a4 ("iio: acpi: Add iio_get_acpi_device_name_and_data() helper function")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

This is counter intuitive as usual expectation would be no side effects on an
error return.  How hard to fix all the users to initialize to NULL if they
care about that?

There is still a chance we set it to NULL in here anyway, but that should only happen
if we know the return is good in the sense of no error (missing ACPI etc)
but not necessarily that dev_name() won't return NULL.

Don't think dev_name() can currently return NULL but 'maybe' it could...



> ---
>  drivers/iio/industrialio-acpi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/industrialio-acpi.c b/drivers/iio/industrialio-acpi.c
> index d67a43843799..33c737c7a2f8 100644
> --- a/drivers/iio/industrialio-acpi.c
> +++ b/drivers/iio/industrialio-acpi.c
> @@ -102,13 +102,17 @@ EXPORT_SYMBOL_GPL(iio_read_acpi_mount_matrix);
>   * NOTE: This helper function exists only for backward compatibility,
>   * do not use in a new code!
>   *
> - * Returns: ACPI device instance name or %NULL.
> + * Returns: ACPI device instance name or %NULL When returning %NULL, the @data,
> + * if provided, will be also initialised to %NULL.
>   */
>  const char *iio_get_acpi_device_name_and_data(struct device *dev, const void **data)
>  {
>  	const struct acpi_device_id *id;
>  	acpi_handle handle;
>  
> +	if (data)
> +		*data = NULL;
> +
>  	handle = ACPI_HANDLE(dev);
>  	if (!handle)
>  		return NULL;