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

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Message-ID: <2023072526-reissue-uplifting-5674@gregkh>
Date:   Tue, 25 Jul 2023 17:12:01 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dingyan Li <18500469033@....com>
Cc:     Oliver Neukum <oneukum@...e.com>, 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

On Tue, Jul 25, 2023 at 10:40:10PM +0800, Dingyan Li wrote:
> 
> 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.

How exactly would that work?  Remember, new kernels still need to work
with old userspace code.

> 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.

We can not "force" anyone to change, that's not how the kernel works,
sorry.

greg k-h