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 82CBEC76196 for ; Mon, 3 Apr 2023 14:56:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pjLap-0002o8-4X; Mon, 03 Apr 2023 10:55:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pjLan-0002nk-V4 for qemu-devel@nongnu.org; Mon, 03 Apr 2023 10:55:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pjLam-0002kO-4x for qemu-devel@nongnu.org; Mon, 03 Apr 2023 10:55:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680533731; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5gPObiWENA9vveWWrWPkBSYV+HErfBasOwTA6nLpBJ0=; b=AhvqWx/1M6M8Cxs++LrM6N5cLTkIVnGhNNP30FGS0GURE9KansccWI7cUnL08xeEvsKbiI N6ZUty+mFTnosmIJObQ6iIm8tSBWsYuNsCyhW8AVuAxKcICnTjHMbH9E03BJMpXcj3sj9e BtpHflrrj/mpUIwIMjYbbO0oCX01MKQ= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-612-2GoGCOxhPHO_xzDJhtCarw-1; Mon, 03 Apr 2023 10:55:27 -0400 X-MC-Unique: 2GoGCOxhPHO_xzDJhtCarw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 90C131C12987; Mon, 3 Apr 2023 14:55:26 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.52]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6F4021121314; Mon, 3 Apr 2023 14:55:25 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 50CD621E6926; Mon, 3 Apr 2023 16:55:23 +0200 (CEST) From: Markus Armbruster To: Alex =?utf-8?Q?Benn=C3=A9e?= Cc: qemu-devel@nongnu.org, Thomas Huth , Warner Losh , Ryo ONODERA , Kevin Wolf , Beraldo Leal , Wainer dos Santos Moschetta , Hanna Reitz , qemu-block@nongnu.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Kyle Evans , Reinoud Zandijk , Michael Tokarev Subject: Re: [PATCH 04/11] qemu-options: finesse the recommendations around -blockdev References: <20230330101141.30199-1-alex.bennee@linaro.org> <20230330101141.30199-5-alex.bennee@linaro.org> <871ql1lc2z.fsf@pond.sub.org> <87mt3pm6tf.fsf@linaro.org> Date: Mon, 03 Apr 2023 16:55:23 +0200 In-Reply-To: <87mt3pm6tf.fsf@linaro.org> ("Alex =?utf-8?Q?Benn=C3=A9e=22's?= message of "Mon, 03 Apr 2023 14:16:36 +0100") Message-ID: <871ql19fs4.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org Alex Benn=C3=A9e writes: > Markus Armbruster writes: > >> Alex Benn=C3=A9e writes: >> >>> We are a bit premature in recommending -blockdev/-device as the best >>> way to configure block devices, especially in the common case. >>> Improve the language to hopefully make things clearer. >>> >>> Suggested-by: Michael Tokarev >>> Signed-off-by: Alex Benn=C3=A9e >>> --- >>> qemu-options.hx | 8 ++++++-- >>> 1 file changed, 6 insertions(+), 2 deletions(-) >>> >>> diff --git a/qemu-options.hx b/qemu-options.hx >>> index 59bdf67a2c..9a69ed838e 100644 >>> --- a/qemu-options.hx >>> +++ b/qemu-options.hx >>> @@ -1143,10 +1143,14 @@ have gone through several iterations as the fea= ture set and complexity >>> of the block layer have grown. Many online guides to QEMU often >>> reference older and deprecated options, which can lead to confusion. >>>=20=20 >>> -The recommended modern way to describe disks is to use a combination of >>> +The most explicit way to describe disks is to use a combination of >>> ``-device`` to specify the hardware device and ``-blockdev`` to >>> describe the backend. The device defines what the guest sees and the >>> -backend describes how QEMU handles the data. >>> +backend describes how QEMU handles the data. The ``-drive`` option >>> +combines the device and backend into a single command line options >>> +which is useful in the majority of cases. >> >> -drive may look simpler from afar, but it really is a hot mess. Sadly, >> we can't get rid of it until we find a replacement for configuring >> onboard block devices. We might be able to clean it up some if we >> accept compatibility breaks. A new convenience option would be less >> confusing, I guess. > > This is only a partial revert of the original wording which others have > pointed out was a little too prescriptive. I believe the case of > snapshot was one where a pure device/blockdev command line is hard to > use.=20 > >>> Older options like ``-hda`` >>> +bake in a lot of assumptions from the days when QEMU was emulating a >>> +legacy PC, they are not recommended for modern configurations. >>>=20=20 >>> ERST >> >> These older options and the non-option argument are simple macros for >> -drive: >> >> IMG-FILE -drive index=3D0,file=3DIMG-FILE,media= =3Ddisk >> -hda IMG-FILE -drive index=3D0,file=3DIMG-FILE,media= =3Ddisk >> -hdb IMG-FILE -drive index=3D1,file=3DIMG-FILE,media= =3Ddisk >> -hdc IMG-FILE -drive index=3D2,file=3DIMG-FILE,media= =3Ddisk >> -hdd IMG-FILE -drive index=3D3,file=3DIMG-FILE,media= =3Ddisk >> -cdrom IMG-FILE -drive index=3D2,file=3DIMG-FILE,media= =3Dcdrom >> -fda IMG-FILE -drive if=3Dfloppy,index=3D0,file=3DIMG-= FILE >> -fdb IMG-FILE -drive if=3Dfloppy,index=3D1,file=3DIMG-= FILE >> -mtdblock IMG-FILE -drive if=3Dmtd,file=3DIMG-FILE >> -sd IMG-FILE -drive if=3Dsd,file=3DIMG-FILE >> -pflash IMG-FILE -drive if=3Dpflash,file=3DIMG-FILE >> >> What assumptions do you have in mind? > > I was under the impression things like -hda wouldn't work say on an Arm > machine because you don't know what sort of interface you might be > using and -hda implies IDE. Where is this macro substitution done? qemu_init() calls drive_add() for all these options. drive_add(TYPE, INDEX, FILE, OPTSTR) creates a QemuOpts in group "drive". It sets "if" to if_name[TYPE] unless TYPE is IF_DEFAULT, "index" to INDEX unless it's negative, and "file" to FILE unless it's null. Then it parses OPTSTR on top. For -hdX, the call looks like drive_add(IF_DEFAULT, popt->index - QEMU_OPTION_hda, optarg, HD_OPTS); We pass IF_DEFAULT, so "if" remains unset. "index" is set to 0 for -hda, 1, for -hdb and so forth. "file" is set to the option argument. Since HD_OPTS is "media=3Ddisk", we set "media" to "disk". The QemuOpts in config group "drive" get passed to drive_new() via drive_init_func(). Unset "if" defaults to the current machine's class's block_default_type. If a machine doesn't set this member explicitly, it remains zero, which is IF_NONE. Documented in blockdev.h: typedef enum { IF_DEFAULT =3D -1, /* for use with drive_add() only */ /* * IF_NONE must be zero, because we want MachineClass member ---> * block_default_type to default-initialize to IF_NONE */ IF_NONE =3D 0, IF_IDE, IF_SCSI, IF_FLOPPY, IF_PFLASH, IF_MTD, IF_SD, IF_VIRTIO, IF= _XEN, IF_COUNT } BlockInterfaceType; Questions? >> I think you need at least Kevin's Acked-by for this. > > In the ideal world I could convince the block maintainers to write a new > section to the manual that explains the theory behind the block > subsystem and how things interact and are put together. Until then this > is merely a sticking plaster to make the manual a little more > authoritative than then numerous example command lines our users blindly > copy from online blog posts. > > Of course we could* always ask our new AI overlords: > [...] > * just because we could doesn't mean we should Heh!