Re: [Xen-devel] [PATCH 9/9] xenstore: when running in mini-os use printk for diagnostic messages

[Juergen Gross <jgross@xxxxxxxx>]

On 15/12/15 13:52, Ian Campbell wrote:
> On Tue, 2015-12-15 at 13:47 +0100, Juergen Gross wrote:
>> On 15/12/15 13:31, Ian Campbell wrote:
>>> On Fri, 2015-12-11 at 16:47 +0100, Juergen Gross wrote:
>>>> Xenstore messages for diagnostic purposes are lost today in case
>>>> xenstore is running under mini-os instead in a dom0 daemon.
>>>
>>> Where does vfprintf end up under mini-os?
>>
>> TBH: I just couldn't find it. I tried to get some diagnostics when
>> I started this work and couldn't find any place where the messages
>> would occur.
>>
>>>> Use printk of mini-os in this situation.
>>>
>>> and this now ends up on the console and (for a debug h/v) in the xen
>>> dmesg,
>>> is that right?
>>
>> The console of the xenstore domain seems to be a little bit special, as
>> there is no component up to now writing the information needed to
>> connect xenconsoled to the xenstore domain. This could be the reason I
>> wasn't able to see any message printed via vfprintf. :-(
> 
> That sounds probable.
> 
>> So in the end it will be part of xen dmesg.
> 
> Only for a debug=y Xen, not for a release build IIRC, unless you added some
> other privilege along with your new flag which I missed.

No, this is correct.

>>  And this is where it should
>> be, as such messages will be needed in case of xenstore domain not
>> working properly. And I think it's console can be accessed by any means
>> only in case of a working xenstore. :-)
> 
> An alternative would be init-xenstore-domain to daemonize and take on
> respoibility for consuming the console ring and throwing it into a file?

Interesting idea. I'll try this.


Juergen


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