netdev - Re: [PATCH] net: phy: update fields of mii_ioctl

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Date: Sat, 20 Apr 2024 10:00:54 +0200
From: Heiner Kallweit <hkallweit1@...il.com>
To: renjun wang <renjunw0@...mail.com>, andrew@...n.ch, linux@...linux.org.uk
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: update fields of mii_ioctl_data for
 transferring C45 data.

On 20.04.2024 02:41, renjun wang wrote:
> The phy_id is used as u32 type in function mdio_phy_id_is_c45()
> with the 30th bit for distinguishing C22 and C45. The reg_num is
> also used as u32 type in function mdiobus_c45_read() or someplace
> else. For more C45 information needed and data structure alignment
> consideration, change these two fields to __u32 type which can make

What do you mean with alignment consideration?

> user space program transferring clause 45 type information to kernel
> directly.
> 

With this change you break userspace. And in general: If you make
such a change, you should also use it.

> Signed-off-by: renjun wang <renjunw0@...mail.com>
> ---
>  include/uapi/linux/mii.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/mii.h b/include/uapi/linux/mii.h
> index 39f7c44baf53..68c085b049de 100644
> --- a/include/uapi/linux/mii.h
> +++ b/include/uapi/linux/mii.h
> @@ -176,8 +176,8 @@
>  
>  /* This structure is used in all SIOCxMIIxxx ioctl calls */
>  struct mii_ioctl_data {
> -	__u16		phy_id;
> -	__u16		reg_num;
> +	__u32		phy_id;
> +	__u32		reg_num;
>  	__u16		val_in;
>  	__u16		val_out;
>  };