linux-kernel - Re: [PATCH] USB: cdc-acm: expose serial close_delay and closing

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Message-ID: <6db3bf2b-b284-7e17-8c42-582a5c7addef@suse.com>
Date:   Thu, 24 Aug 2023 10:21:19 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Simon Arlott <simon@...iron.net>, Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait
 in sysfs

On 23.08.23 22:37, Simon Arlott wrote:

Hi,

I am terribly sorry, but this has to be a hard NO.
This patch has an unsurmountable problem.
Reasons below.

> The serial_core driver (ttySx) exposes its supported ioctl values as
> read-only sysfs attributes. Add read-write sysfs attributes "close_delay"
> and "closing_wait" to cdc-acm (ttyACMx) devices. These are the same as the

If the tty core does not export them as writable it presumably has reasons
for that. We cannot circumvent those reasons in a particular driver unless
there are very special circumstances that make the driver a special case.

The correct way to deal with this issue would be a proposal to change
the generic serial code. Even there I am sceptical because we would carry
the code duplication forever. ioctl() is the way you set the parameters
for a serial port in a Unix system. We have tools for that. Adding a second method
is problematic.
But that is not for me to decide. As far as CDC-ACM, however, is concerned,
I must reject this patch, because it fundamentally does something that should
not be done, definitely not at this layer.

	Sorry
		Oliver

> Signed-off-by: Simon Arlott <simon@...iron.net>
Nacked-by: Oliver Neukum <oneukum@...e.com>