linux-kernel - Re: [PATCH v2 1/8] tty: add a poll() callback in struct tty

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Date:   Wed, 14 Jun 2017 02:15:05 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Tal Shorer <tal.shorer@...il.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, gregkh@...uxfoundation.org,
        balbi@...nel.org, corbet@....net
Subject: Re: [PATCH v2 1/8] tty: add a poll() callback in struct
 tty_operations

On Tue, 13 Jun 2017 09:52:07 +0300
Tal Shorer <tal.shorer@...il.com> wrote:

> If a tty driver wants to notify the user of some exceptional event,
> such as a usb cdc acm device set_line_coding event, it needs a way to
> modify the mask returned by poll() and possible also add wait queues.
> In order to do that, we allow the driver to supply a poll() callback
> of its own, which will be called in n_tty_poll().
> 
> Signed-off-by: Tal Shorer <tal.shorer@...il.com>

You might be in any line discipline so you need to support that for each
ldisc that supports poll(). Also what do I do when I get an exception
event - what does it mean, how do I understand that, are you proposing a
standardized meaning ? Have you checked whether that conflicts with SuS
v3 or POSIX ? What will it do with existing code.

At the very least it probably has to be something you turn on, and you
might then want to model it on the pty/tty interface logic and extend
TIOCPKT a shade.

Alan