Re: [PATCH 01/27] driver core: Constify driver API device_find_child()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Aug 11, 2024 at 10:24:52AM +0800, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@quicinc.com>
> 
> Constify the following driver API:
> struct device *device_find_child(struct device *dev, void *data,
> 		int (*match)(struct device *dev, void *data));
> to
> struct device *device_find_child(struct device *dev, const void *data,
>                                  device_match_t match);
> typedef int (*device_match_t)(struct device *dev, const void *data);
> Since it should not modify caller's match data @*data.
> 
> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
> ---
>  drivers/base/core.c    | 11 +++--------
>  include/linux/device.h |  4 ++--
>  2 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 3f3ebdb5aa0b..f152e0f8fb03 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -4062,8 +4062,8 @@ EXPORT_SYMBOL_GPL(device_for_each_child_reverse);
>   *
>   * NOTE: you will need to drop the reference with put_device() after use.
>   */
> -struct device *device_find_child(struct device *parent, void *data,
> -				 int (*match)(struct device *dev, void *data))
> +struct device *device_find_child(struct device *parent, const void *data,
> +				 device_match_t match)
>  {
>  	struct klist_iter i;
>  	struct device *child;
> @@ -4108,11 +4108,6 @@ struct device *device_find_child_by_name(struct device *parent,
>  }
>  EXPORT_SYMBOL_GPL(device_find_child_by_name);
>  
> -static int match_any(struct device *dev, void *unused)
> -{
> -	return 1;
> -}
> -
>  /**
>   * device_find_any_child - device iterator for locating a child device, if any.
>   * @parent: parent struct device
> @@ -4124,7 +4119,7 @@ static int match_any(struct device *dev, void *unused)
>   */
>  struct device *device_find_any_child(struct device *parent)
>  {
> -	return device_find_child(parent, NULL, match_any);
> +	return device_find_child(parent, NULL, device_match_any);
>  }
>  EXPORT_SYMBOL_GPL(device_find_any_child);
>  
> diff --git a/include/linux/device.h b/include/linux/device.h
> index b2423fca3d45..76f10bdbb4ea 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1073,8 +1073,8 @@ int device_for_each_child(struct device *dev, void *data,
>  			  int (*fn)(struct device *dev, void *data));
>  int device_for_each_child_reverse(struct device *dev, void *data,
>  				  int (*fn)(struct device *dev, void *data));
> -struct device *device_find_child(struct device *dev, void *data,
> -				 int (*match)(struct device *dev, void *data));
> +struct device *device_find_child(struct device *dev, const void *data,
> +				 device_match_t match);
>  struct device *device_find_child_by_name(struct device *parent,
>  					 const char *name);
>  struct device *device_find_any_child(struct device *parent);
> 
> -- 
> 2.34.1
> 

This patch breaks the build:

./include/linux/device.h:1077:6: error: unknown type name 'device_match_t'
 1077 |                                  device_match_t match);
      |                                  ^
1 error generated.
make[2]: *** [scripts/Makefile.build:117: arch/x86/kernel/asm-offsets.s] Error 1
make[1]: *** [/mnt/fast_t2/linux/work/driver-core/Makefile:1193: prepare0] Error 2

How did you test it?

And as you are changing the parameters here, doesn't the build break
also because of that?

thanks,

greg k-h