Re: [PATCH 2/2] expert_mode: Add a new configuration option for expert users.

From: George Dunlap <george.dunlap@eu.citrix.com>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad@kernel.org>,
	xen-devel@lists.xensource.com,
	Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH 2/2] expert_mode: Add a new configuration option for expert users.
Date: Wed, 17 Jul 2013 12:13:31 +0100	[thread overview]
Message-ID: <51E67C5B.8030006@eu.citrix.com> (raw)
In-Reply-To: <1374059533.8960.31.camel@kazak.uk.xensource.com>

On 17/07/13 12:12, Ian Campbell wrote:
> On Wed, 2013-07-17 at 12:03 +0100, George Dunlap wrote:
>> On 17/07/13 11:56, Ian Jackson wrote:
>>> Ian Campbell writes ("Re: [Xen-devel] [PATCH 2/2] expert_mode: Add a new configuration option for expert users."):
>>>> On Fri, 2013-07-12 at 14:08 -0400, Konrad Rzeszutek Wilk wrote:
>>>>> This could also be called 'seatbelt' option.
>>>>>
>>>>> libxl has a variety of checks where it will fail out an operation
>>>>> unless the user has provided an --force (or --ignore) parameter.
>>>>> Currently one such check is for the 'vcpu-set' command which
>>>>> will error out if the count of virtual cpus is greater than the
>>>>> physical cpus. This parameter will ignore such checks and allow
>>>>> the user to do the operations without the need for override flags.
>>>> Does this overlap  somewhat with various commands which individually
>>>> take a -f(orce) option?
>>> Clearly it should disable all of those -f's too.
>>>
>>>>> +=item B<expert_mode=BOOLEAN>
>>>>> +
>>>>> +Do not act on host performed checks that might lead to performance
>>>>> +degradations. Currently checks are made for following operations:
>>>>> + - C<vcpu-set> - if the number of VCPUs set for a guest is higher than the
>>>>> +   physical count the operation will error out.
>>> I don't think this is a very coherent specification.  Surely it should
>>> override "all -f options" or something similar.
>> I think that makes sense for some but not all.  For example, for "xl
>> shutdown", -f means "send an ACPI event if no PV drivers are detected".
>> I don't think we'd want to change that behavior with such a switch.
>> (Arguably -f was the wrong option to use for that in the first place,
>> but it's a bit late for that now.)
> That's -F (for fallback not force), deliberately avoiding -f for the
> reasons you might think.
>
> If "xl shutdown -f" were to do anything it would probably be to act as
> "xl destroy" (nb I don't think we should actually do that...)

Ah, right.  That makes sense.

  -G