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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 42D21C04A68 for ; Thu, 28 Jul 2022 17:10:54 +0000 (UTC) Received: from localhost ([::1]:36256 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oH72D-0005le-6c for qemu-devel@archiver.kernel.org; Thu, 28 Jul 2022 13:10:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42368) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oH70a-0004lf-E9 for qemu-devel@nongnu.org; Thu, 28 Jul 2022 13:09:12 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39591) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oH70X-0000pN-Mw for qemu-devel@nongnu.org; Thu, 28 Jul 2022 13:09:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659028144; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DogADKDCHu9M+X1pX23VQYzagzQQ9RO4hkFFwkg90B8=; b=NBNNGDz67LiXSrkWvqbYKk1VImJ5smdItSLa7cmfC3rUOUFamXAc0mbwFhLItUyVdGAR0w dH2VdDkImkLkfoQZrOy/4fK3qJ2IuFFUWj4TKwL5uw0LKtW0Il0TksvH7DqwG1qAn5G1nq KxGN8YPUQaaeRZVr7BrTQOexh6QRoOA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-50-6wLUm-IRPUu0CNEkCYNGQQ-1; Thu, 28 Jul 2022 13:09:03 -0400 X-MC-Unique: 6wLUm-IRPUu0CNEkCYNGQQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BACA51824600; Thu, 28 Jul 2022 17:09:01 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 87EAB2026D64; Thu, 28 Jul 2022 17:08:58 +0000 (UTC) Date: Thu, 28 Jul 2022 19:08:57 +0200 From: Kevin Wolf To: Markus Armbruster Cc: Peter Maydell , Hao Wu , richard.henderson@linaro.org, qemu-arm@nongnu.org, qemu-devel@nongnu.org, venture@google.com, Avi.Fishman@nuvoton.com, kfting@nuvoton.com, hskinnemoen@google.com, f4bug@amsat.org, bin.meng@windriver.com, qemu-block@nongnu.org, thuth@redhat.com, Hanna Reitz Subject: Re: [PATCH v5 5/8] blockdev: Add a new IF type IF_OTHER Message-ID: References: <20220714182836.89602-1-wuhaotsh@google.com> <20220714182836.89602-6-wuhaotsh@google.com> <87ilnuda33.fsf@pond.sub.org> <878rodxpeq.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878rodxpeq.fsf@pond.sub.org> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 28.07.2022 um 16:50 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > Am 28.07.2022 um 11:46 hat Peter Maydell geschrieben: > >> On Wed, 27 Jul 2022 at 20:03, Kevin Wolf wrote: > >> > > >> > Am 18.07.2022 um 11:49 hat Markus Armbruster geschrieben: > >> > > An OTP device isn't really a parallel flash, and neither are eFuses. > >> > > More fast-and-lose use of IF_PFLASH may exist in the tree, and maybe of > >> > > other interface types, too. > >> > > > >> > > This patch introduces IF_OTHER. The patch after next uses it for an > >> > > EEPROM device. > >> > > > >> > > Do we want IF_OTHER? > >> > > >> > What would the semantics even be? Any block device that doesn't pick up > >> > a different category may pick up IF_OTHER backends? > >> > > >> > It certainly feels like a strange interface to ask for "other" disk and > >> > then getting as surprise what this other thing might be. It's > >> > essentially the same as having an explicit '-device other', and I > >> > suppose most people would find that strange. > >> > > >> > > If no, I guess we get to abuse IF_PFLASH some more. > >> > > > >> > > If yes, I guess we should use IF_PFLASH only for actual parallel flash > >> > > memory going forward. Cleaning up existing abuse of IF_PFLASH may not > >> > > be worth the trouble, though. > >> > > > >> > > Thoughts? > >> > > >> > If the existing types aren't good enough (I don't have an opinion on > >> > whether IF_PFLASH is a good match), let's add a new one. But a specific > >> > new one, not just "other". > >> > >> I think the common thread is "this isn't what anybody actually thinks > >> of as being a 'disk', but we would like to back it with a block device > >> anyway". That can cover a fair range of possibilities... > > > > How confident are we that no board will ever have two devices of this > > kind? > > > > As long as every board has at most one, if=other is a bad user interface > > in terms of descriptiveness, but still more or less workable as long as > > you know what it means for the specific board you use. > > > > But if you have more than one device, it becomes hard to predict which > > device gets which backend - it depends on the initialisation order in > > the code then, > > Really? Board code should use IF_OTHER devices just like it uses the > other interface types, namely connecting each frontend device to a > backend device with a well-known and fixed interface type and index (or > bus and unit instead, where appropriate). > > > and I'm pretty sure that this isn't something that should > > have significance in external interfaces and therefore become a stable > > API. > > I agree that "implied by execution order" is a bad idea: commit > 95fd260f0a "blockdev: Drop unused drive_get_next()". Ah good, I was indeed thinking of something drive_get_next()-like. In case the board works with explicit indices, the situation is not as bad as I was afraid. It will certainly be workable (even if not obvious) for any boards that have a fixed number of devices with block backends, which should cover everything we're intending to cover here. I still consider if=other a bad user interface because what it means is completely opaque, but if that's okay for you in your board, who am I to object. (Of course, the real solution would be having a generic way to set qdev properties for on-board devices. I'm not expecting that we're getting this anytime soon, though.) Kevin