Re: [Xen-devel] [PATCH v2 1/2] xen: add interface for obtaining .config from hypervisor

From: Juergen Gross <jgross@suse.com>
To: George Dunlap <george.dunlap@citrix.com>, Wei Liu <wei.liu2@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	IanJackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel@lists.xenproject.org,
	Daniel De Graaf <dgdegra@tycho.nsa.gov>
Subject: Re: [Xen-devel] [PATCH v2 1/2] xen: add interface for obtaining .config from hypervisor
Date: Mon, 5 Aug 2019 17:12:56 +0200	[thread overview]
Message-ID: <00f0c1ca-4209-9959-cd43-0a548f651f79@suse.com> (raw)
In-Reply-To: <3037198b-fe2a-5746-2ffa-1d17fbb6547c@citrix.com>

On 05.08.19 17:07, George Dunlap wrote:
> On 4/4/19 2:35 PM, Juergen Gross wrote:
>> On 04/04/2019 15:27, Wei Liu wrote:
>>> On Fri, Mar 15, 2019 at 05:29:28PM +0100, Juergen Gross wrote:
>>>> On 15/03/2019 16:55, Andrew Cooper wrote:
>>>>> On 14/03/2019 11:59, Juergen Gross wrote:
>>>>>> @@ -1100,6 +1100,20 @@ typedef struct xen_sysctl_cpu_policy xen_sysctl_cpu_policy_t;
>>>>>>   DEFINE_XEN_GUEST_HANDLE(xen_sysctl_cpu_policy_t);
>>>>>>   #endif
>>>>>>   
>>>>>> +/*
>>>>>> + * XEN_SYSCTL_get_config
>>>>>> + *
>>>>>> + * Return gzip-ed .config file
>>>>>
>>>>> I don't think it is wise to bake gzip into the API.  These days, there
>>>>> really are better options than gzip both in terms of compression ratio
>>>>> and decompress speed.
>>>>>
>>>>> I'd suggest just saying "file may be compressed" and leave it up to the
>>>>> packagers build system and `xl` choices to agree on which compression
>>>>> (if any) to use.
>>>>
>>>> I am not convinced this is a good idea. I think the data format should
>>>> be specified.
>>>>
>>>> And TBH: the difference in size for a rather "normal" .config is about
>>>> 50 bytes (I tried gzip, xz and bzip2 with gzip producing the smallest
>>>> result).
>>>
>>> Has this been resolved?
>>>
>>> I don't really have an opinion on this.
>>
>> I got no reply for that answer.
> 
> You don't need a reply; if a suggestion is made, and you explain why you
> don't like it, then it's up to the other person to unabiguously Nack it
> if they don't like it; silence is interpreted as consent.
> 
> To move this forward, I'd suggest re-posting it, adding a comment about
> the choice of compression algorithm in the commit message.

At the summit we had a discussion about a simple name-value store in the
hypervisor for e.g. communicating mitigation settings or runtime param
settings to at least dom0. The .config used for building Xen was agreed
to be another candidate for that interface.

I wanted to have a look at that when I'm finished with other urgent work
I'm actually doing.

Juergen

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