linux-kernel - Re: [PATCH v2] staging: greybus: use inline function for macros

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Message-ID: <2e869677-2693-6419-ea25-f0cc2efcf3dd@ieee.org>
Date:   Tue, 21 Mar 2023 13:50:19 -0500
From:   Alex Elder <elder@...e.org>
To:     Menna Mahmoud <eng.mennamahmoud.mm@...il.com>,
        gregkh@...uxfoundation.org
Cc:     outreachy@...ts.linux.dev, johan@...nel.org, elder@...nel.org,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
        Julia Lawall <julia.lawall@...ia.fr>
Subject: Re: [PATCH v2] staging: greybus: use inline function for macros

On 3/21/23 1:34 PM, Menna Mahmoud wrote:
> Convert `to_gbphy_dev` and `to_gbphy_driver` macros into a
> static inline function.
> 
> It is not great to have macros that use the `container_of` macro,
> because from looking at the definition one cannot tell what type
> it applies to.
> 
> One can get the same benefit from an efficiency point of view
> by making an inline function.
> 
> Suggested-by: Julia Lawall <julia.lawall@...ia.fr>
> Signed-off-by: Menna Mahmoud <eng.mennamahmoud.mm@...il.com>

I'm sorry if this conflicts with what others have said.

But the use of a macro (with a container_of() right-hand
side) to get at the structure containing a field pointer
is a widely-used idiom throughout the kernel.

What you propose achieves the same result but I would
lean toward keeping it as a macro, mainly because it
is so common.

					-Alex
> ---
> changes in v2:
> 	-send patch as a single patch.
> 	-edit the name of struct object.
> 	-edit commit message.
> ---
>   drivers/staging/greybus/gbphy.h | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/greybus/gbphy.h b/drivers/staging/greybus/gbphy.h
> index d4a225b76338..e7ba232bada1 100644
> --- a/drivers/staging/greybus/gbphy.h
> +++ b/drivers/staging/greybus/gbphy.h
> @@ -15,7 +15,10 @@ struct gbphy_device {
>   	struct list_head list;
>   	struct device dev;
>   };
> -#define to_gbphy_dev(d) container_of(d, struct gbphy_device, dev)
> +static inline struct gbphy_device *to_gbphy_dev(const struct device *_dev)
> +{
> +	return container_of(_dev, struct gbphy_device, dev);
> +}
>   
>   static inline void *gb_gbphy_get_data(struct gbphy_device *gdev)
>   {
> @@ -43,7 +46,10 @@ struct gbphy_driver {
>   
>   	struct device_driver driver;
>   };
> -#define to_gbphy_driver(d) container_of(d, struct gbphy_driver, driver)
> +static inline struct gbphy_driver *to_gbphy_driver(struct device_driver *drv)
> +{
> +	return container_of(drv, struct gbphy_driver, driver);
> +}
>   
>   int gb_gbphy_register_driver(struct gbphy_driver *driver,
>   			     struct module *owner, const char *mod_name);