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Re: [PATCH for-6.1 0/1] machine: Disallow specifying topology parameters

From: wangyanan (Y)
Subject: Re: [PATCH for-6.1 0/1] machine: Disallow specifying topology parameters as zero
Date: Thu, 22 Jul 2021 18:59:52 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

On 2021/7/22 14:02, Cornelia Huck wrote:
On Thu, Jul 22 2021, Yanan Wang <wangyanan55@huawei.com> wrote:

In the SMP configuration, we should either specify a topology
parameter with a reasonable value (equal to or greater than 1)
or just leave it omitted and QEMU will calculate its value.
Configurations which explicitly specify the topology parameters
as zero like "sockets=0" are meaningless, so disallow them.

However; the commit 1e63fe685804d
(machine: pass QAPI struct to mc->smp_parse) has documented that
'0' has the same semantics as omitting a parameter in the qapi
comment for SMPConfiguration. So this patch fixes the doc and
also adds the corresponding sanity check in the smp parsers.
Are we expecting any real users to have used that 'parameter=0'
behaviour? I expect that libvirt and other management software already
did the right thing; unfortunately, sometimes weird configuration lines
tend to persist in search results.
I think there may not any users who have already used a configuration
with explicit "parameter=0", instead it should have been just omitted.
Yes, libvirt now rejects "parameter=0" when parsing XML, but we now
still allows "parameter=0" in the direct QEMU cmdlines. If we hope to
disallow this kind of config thoroughly, we'd better also have a sanity
check in QEMU.

This patch originly comes form [1], and it was suggested that
this patch fixing the doc should be sent for 6.1 to avoid a
deprecation process in the future.

[1] YPWsThPiZa3mF+zp@redhat.com/">https://lore.kernel.org/qemu-devel/YPWsThPiZa3mF+zp@redhat.com/

Yanan Wang (1):
   machine: Disallow specifying topology parameters as zero

  hw/core/machine.c | 30 ++++++++++++++++++++++--------
  hw/i386/pc.c      | 33 ++++++++++++++++++++++++---------
  qapi/machine.json |  6 +++---
  3 files changed; 49 insertions(+); 20 deletions(-)

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