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 243B1C61DA4 for ; Thu, 2 Feb 2023 09:19:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pNVj4-0005Mw-Fd; Thu, 02 Feb 2023 04:17:50 -0500 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 1pNViw-0005KD-Q3 for qemu-devel@nongnu.org; Thu, 02 Feb 2023 04:17:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pNViu-0004EG-Ng for qemu-devel@nongnu.org; Thu, 02 Feb 2023 04:17:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675329460; h=from:from:reply-to: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=wPGOJ+V0BdxyGLt3CI7w4MFc4T7fXqU3llOo0MnH4S4=; b=cGjGtjCY1uHUxJuBx8OqNjbI5k/tZQE8yfsjHg3uKqxDvfgxGdO9KTpxHFp/l4AKoRtIDR /9U8FfXbdsLBcDr8YkmlmUisF9c85/iObtCRw8+BYCDApNgS+1GmdUl7PboOq3aWlbgWTC zBFNL6iLOTtvRMRC0/4XZHjxELuJLS0= 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-651-ngG7xxZiMBeznrrAmhgaMQ-1; Thu, 02 Feb 2023 04:17:37 -0500 X-MC-Unique: ngG7xxZiMBeznrrAmhgaMQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AAAC13C18345; Thu, 2 Feb 2023 09:17:36 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B25A9404CD81; Thu, 2 Feb 2023 09:17:35 +0000 (UTC) Date: Thu, 2 Feb 2023 09:17:33 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Kevin Wolf , mjt@tls.msk.ru Subject: Re: [PATCH 3/5] docs: flesh out raw format driver description Message-ID: References: <20230201211234.301918-1-stefanha@redhat.com> <20230201211234.301918-4-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230201211234.301918-4-stefanha@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Feb 01, 2023 at 04:12:32PM -0500, Stefan Hajnoczi wrote: > Modernize the description and document the size=/offset= runtime > options. > > Signed-off-by: Stefan Hajnoczi > --- > docs/system/qemu-block-drivers.rst.inc | 32 ++++++++++++++++++++++---- > 1 file changed, 27 insertions(+), 5 deletions(-) > > diff --git a/docs/system/qemu-block-drivers.rst.inc b/docs/system/qemu-block-drivers.rst.inc > index be6eec1eb6..ec9ebb2066 100644 > --- a/docs/system/qemu-block-drivers.rst.inc > +++ b/docs/system/qemu-block-drivers.rst.inc > @@ -16,11 +16,11 @@ options that are supported for it. > .. option:: raw > > Raw disk image format. This format has the advantage of > - being simple and easily exportable to all other emulators. If your > - file system supports *holes* (for example in ext2 or ext3 on > - Linux or NTFS on Windows), then only the written sectors will reserve > - space. Use ``qemu-img info`` to know the real size used by the > - image or ``ls -ls`` on Unix/Linux. > + being simple and easily exportable to all other emulators. Modern > + file systems support *holes* (for example in btrfs/XFS/ext4 on > + Linux or NTFS on Windows) where space is allocated on demand as sectors are > + written. Use ``qemu-img info`` to know the real size used by the image or > + ``ls -ls`` on Unix/Linux. > > Supported create options: > > @@ -33,6 +33,28 @@ options that are supported for it. > for image by writing data to underlying storage. This data may or > may not be zero, depending on the storage location. > > + Supported runtime options: > + > + .. program:: raw > + .. option:: offset > + > + The byte position in the underlying file where the virtual disk starts. > + This is handy when you want to present just a single partition from a > + physical disk as the virtual disk. This option is usually used in > + conjunction with the ``size`` option. > + > + .. option:: size > + > + Limit the virtual disk size to the given number of bytes, regardless of how > + large the underlying file is. This option is usually used in conjunction > + with the ``offset`` option. > + > + Note the raw format can be omitted when no runtime options are being used. In > + that case the raw format does nothing besides forwarding I/O requests to the > + protocol blockdev. You can improve performance slightly by eliminating > + ``--blockdev raw,file=file0,node-name=drive0`` and renaming the "file0" > + blockdev to "drive0". This paragraphs reads a bit softly. I would word this such that we explicitly and strongly recommend against using the 'raw' format driver. Almost no one will have a need for this. All the protocol drivers expose a raw format, which can be consumed directly. So the 'raw' format driver should NEVER be used unless the user needs to apply a limited window over the underlying disk capacity, which is pretty rare. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|