Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754336AbdFNIUy (ORCPT ); Wed, 14 Jun 2017 04:20:54 -0400 Received: from mail-yw0-f193.google.com ([209.85.161.193]:35582 "EHLO mail-yw0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750751AbdFNIUv (ORCPT ); Wed, 14 Jun 2017 04:20:51 -0400 MIME-Version: 1.0 In-Reply-To: <20170614021505.5a915c2b@alans-desktop> References: <1497336734-19368-1-git-send-email-tal.shorer@gmail.com> <1497336734-19368-2-git-send-email-tal.shorer@gmail.com> <20170614021505.5a915c2b@alans-desktop> From: Tal Shorer Date: Wed, 14 Jun 2017 11:20:49 +0300 Message-ID: Subject: Re: [PATCH v2 1/8] tty: add a poll() callback in struct tty_operations To: Alan Cox Cc: linux-doc@vger.kernel.org, "" , USB list , "" , Felipe Balbi , Jonathan Corbet Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1527 Lines: 28 On Wed, Jun 14, 2017 at 4:15 AM, Alan Cox wrote: > On Tue, 13 Jun 2017 09:52:07 +0300 > Tal Shorer 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 > > 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. That would cut it, but TIOCPKT is too coupled with having a linked tty. I could make acm behave like a pty (accept TIOCPKT and issue the ctrl_status bits), but for that I need n_tty to know that packet does not always mean a linked tty is present, and that in case it isn't we take our own ctrl_status bits instead of the link's. I could write a small (inline?) function to fetch the correct ctrl_status bits and put that in n_tty. Does that make sense?