linux-kernel - Re:Re: [PATCH] USB: add usbfs ioctl to get specific superspeedplus rates

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Message-ID: <3018cd33.7ee4.1898d7e4798.Coremail.18500469033@163.com>
Date:   Tue, 25 Jul 2023 22:40:10 +0800 (CST)
From:   "Dingyan Li" <18500469033@....com>
To:     "Oliver Neukum" <oneukum@...e.com>
Cc:     "Greg KH" <gregkh@...uxfoundation.org>, stern@...land.harvard.edu,
        sebastian.reichel@...labora.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH] USB: add usbfs ioctl to get specific superspeedplus
 rates

At 2023-07-25 22:08:44, "Oliver Neukum" <oneukum@...e.com> wrote:
>On 25.07.23 15:54, Dingyan Li wrote:
>
>> If we can't "deprecate" ioctls, can we change the returned contents of existing ones?
>
>No. Absolutely not. That is totally unacceptable. It would be much
>worse than just removing the support.
>
>	Regards
>		Oliver

Got it, I guess this is for backward-compatibility.

I also have another thought. USBDEVFS_CONNINFO_EX is kind of special and
used to retrieve contents of variable length. If you check proc_conninfo_ex(),
I think maybe we can append a new member to "struct usbdevfs_conninfo_ex"
without breaking backward-compatibility.

By this way, we can avoid adding a new ioctl. Or even more aggressively,
drop USBDEVFS_GET_SPEED and force everyone to use USBDEVFS_CONNINFO_EX
since it can also return device speed.

Regards,
Dingyan