From nobody Sat Apr 27 07:31:54 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; envelope-from=libvir-list-bounces@redhat.com; helo=mx1.redhat.com; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=libvir-list-bounces@redhat.com; dmarc=pass(p=none dis=none) header.from=redhat.com Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by mx.zohomail.com with SMTPS id 1548278406127386.6705849689894; Wed, 23 Jan 2019 13:20:06 -0800 (PST) Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1FDBEB083A; Wed, 23 Jan 2019 21:20:03 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5B4485C23D; Wed, 23 Jan 2019 21:20:02 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id D91F93F602; Wed, 23 Jan 2019 21:20:00 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id x0NLJxCP030197 for ; Wed, 23 Jan 2019 16:19:59 -0500 Received: by smtp.corp.redhat.com (Postfix) id 7CA1D5D756; Wed, 23 Jan 2019 21:19:59 +0000 (UTC) Received: from blue.redhat.com (ovpn-117-44.phx2.redhat.com [10.3.117.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6DB255D6A6; Wed, 23 Jan 2019 21:19:56 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org Date: Wed, 23 Jan 2019 15:19:53 -0600 Message-Id: <20190123211953.28578-1-eblake@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-loop: libvir-list@redhat.com Cc: "reviewer:Incompatible changes" , thuth@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org Subject: [libvirt] [PATCH] qemu-nbd: Deprecate qemu-nbd --partition X-BeenThere: libvir-list@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Development discussions about the libvirt library & tools List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: quoted-printable Sender: libvir-list-bounces@redhat.com Errors-To: libvir-list-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Wed, 23 Jan 2019 21:20:04 +0000 (UTC) Content-Type: text/plain; charset="utf-8" The existing qemu-nbd --partition code claims to handle logical partitions up to 8, since its introduction in 2008 (commit 7a5ca86). However, the implementation is bogus (actual MBR logical partitions form a sort of linked list, with one partition per extended table entry, rather than four logical partitions in a single extended table), making the code unlikely to work for anything beyond -P5 on actual guest images. What's more, the code does not support GPT partitions, which are becoming more popular, and maintaining device subsetting in both NBD and the raw device is unnecessary maintenance burden. And nbdkit has just added code to properly handle an arbitrary number of MBR partitions, along with its existing code for handling GPT partitions. Note that obtaining the offsets of a partition can be learned by using 'qemu-nbd -c /dev/nbd0 file.qcow2 && sfdisk --dump /dev/nbd0', but by the time you've done that, you might as well just mount /dev/nbd0p1 that the kernel creates for you. Start the clock on the deprecation cycle, with an example of how to write device subsetting without using -P. Signed-off-by: Eric Blake Reviewed-by: Richard W.M. Jones --- qemu-deprecated.texi | 27 +++++++++++++++++++++++++++ qemu-nbd.texi | 6 ++++-- qemu-nbd.c | 2 ++ 3 files changed, 33 insertions(+), 2 deletions(-) diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 219206a836f..12f8b30943f 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -175,3 +175,30 @@ The above, converted to the current supported format: @subsubsection "irq": "" (since 3.0.0) The ``irq'' property is obsoleted. + +@section Related binaries + +@subsection qemu-nbd --partition (since 4.0.0) + +The ``qemu-nbd --partition $digit'' code (also spelled @option{-P}) +can only handle MBR partitions, and does not correctly handle logical +partitions beyond partition 5. If you know the relative position of +the partition (perhaps by using @code{sfdisk} or similar, either in +the guest or when mapping the entire device through /dev/nbd0 in the +host), you can achieve the effect of exporting just that subset of the +disk by use of the @option{--image-opts} option with a raw blockdev +using the @code{offset} and @code{size} parameters layered on top of +any other existing blockdev. + +For example, if partition 1 is 100MiB starting at 1MiB, the old command + +@example{qemu-nbd -P 1 -f qcow2 file.qcow2} + +can be rewritten as: + +@example{qemu-nbd --image-opts driver=3Draw,offset=3D1M,size=3D100M,file.d= river=3Dqcow2,file.backing.driver=3Dfile,file.backing.filename=3Dfile.qcow2} + +Alternatively, the @code{nbdkit} project provides a more powerful +partition filter on top of its nbd plugin, which can be used to select +an arbitrary MBR or GPT partition on top of any other full-image NBD +export. diff --git a/qemu-nbd.texi b/qemu-nbd.texi index 386bece4680..d0c51828149 100644 --- a/qemu-nbd.texi +++ b/qemu-nbd.texi @@ -56,8 +56,10 @@ auto-detecting. @item -r, --read-only Export the disk as read-only. @item -P, --partition=3D@var{num} -Only expose MBR partition @var{num}. Understands physical partitions -1-4 and logical partitions 5-8. +Deprecated: Only expose MBR partition @var{num}. Understands physical +partitions 1-4 and logical partition 5. New code should instead use +@option{--image-opts} with the raw driver wrapping a subset of the +original image. @item -B, --bitmap=3D@var{name} If @var{filename} has a qcow2 persistent bitmap @var{name}, expose that bitmap via the ``qemu:dirty-bitmap:@var{name}'' context diff --git a/qemu-nbd.c b/qemu-nbd.c index 1f7b2a03f5d..00c07fd27ea 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -787,6 +787,8 @@ int main(int argc, char **argv) flags &=3D ~BDRV_O_RDWR; break; case 'P': + warn_report("The '-P' option is deprecated; use --image-opts w= ith " + "a raw device wrapper for subset exports instead"); if (qemu_strtoi(optarg, NULL, 0, &partition) < 0 || partition < 1 || partition > 8) { error_report("Invalid partition '%s'", optarg); --=20 2.20.1 -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list