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

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.

>  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?


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