From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34D54C282C0 for ; Wed, 23 Jan 2019 11:58:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D7BB20870 for ; Wed, 23 Jan 2019 11:58:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727050AbfAWL64 (ORCPT ); Wed, 23 Jan 2019 06:58:56 -0500 Received: from mx2.suse.de ([195.135.220.15]:34374 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725991AbfAWL64 (ORCPT ); Wed, 23 Jan 2019 06:58:56 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6DC7BAFED; Wed, 23 Jan 2019 11:58:54 +0000 (UTC) Date: Wed, 23 Jan 2019 12:58:51 +0100 Message-ID: From: Takashi Iwai To: Mark Brown Cc: Jaroslav Kysela , alsa-devel@alsa-project.org, arnd@arndb.de, keescook@chromium.org, bgoswami@codeaurora.org, sr@denx.de, gustavo@embeddedor.com, philburk@google.com, willy@infradead.org, mchehab+samsung@kernel.org, sboyd@kernel.org, vkoul@kernel.org, Baolin Wang , daniel.thompson@linaro.org, leo.yan@linaro.org, mathieu.poirier@linaro.org, srinivas.kandagatla@linaro.org, anna-maria@linutronix.de, corbet@lwn.net, jmiller@neverware.com, ckeepax@opensource.wolfsonmicro.com, joe@perches.com, o-takashi@sakamocchi.jp, colyli@suse.de, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] ALSA: core: Add DMA share buffer support In-Reply-To: <20190122202535.GK7579@sirena.org.uk> References: <290f6d3a5fe288b87480cc5fa12c5139728daeca.1547787189.git.baolin.wang@linaro.org> <81e894ba-acad-2fd4-996d-8d35edd8825a@perex.cz> <20190118190805.GF6260@sirena.org.uk> <20190121124053.GA12679@sirena.org.uk> <20190122202535.GK7579@sirena.org.uk> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Jan 2019 21:25:35 +0100, Mark Brown wrote: > > On Mon, Jan 21, 2019 at 03:15:43PM +0100, Jaroslav Kysela wrote: > > Dne 21.1.2019 v 13:40 Mark Brown napsal(a): > > > > It was the bit about adding more extended permission control that I was > > > worried about there, not the initial O_APPEND bit. Indeed the O_APPEND > > > bit sounds like it might also work from the base buffer sharing point of > > > view, I have to confess I'd not heard of that feature before (it didn't > > > come up in the discussion when Eric raised this in Prague). > > > With permissions, I meant to make possible to restrict the file > > descriptor operations (ioctls) for the depending task (like access to > > the DMA buffer, synchronize it for the non-coherent platforms and maybe > > read/write the actual position, delay etc.). It should be relatively > > easy to implement using the snd_pcm_file structure. > > Right, that's what I understood you to mean. If you want to have a > policy saying "it's OK to export a PCM file descriptor if it's only got > permissions X and Y" the security module is going to need to know about > the mechanism for setting those permissions. With dma_buf that's all a > bit easier as there's less new stuff, though I've no real idea how much > of a big deal that actually is. There are many ways to implement such a thing, yeah. If we'd need an implementation that is done solely in the sound driver layer, I can imagine to introduce either a new ioctl or an open flag (like O_EXCL) to specify the restricted sharing. That is, a kind of master / slave model where only the master is allowed to manipulate the stream while the slave can mmap, read/write and get status. thanks, Takashi