Re: [PATCH 07/18] mini-os: avoid crash if no console is provided

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

On 01/12/2012 05:03 AM, Ian Campbell wrote:
> On Wed, 2012-01-11 at 17:21 +0000, Daniel De Graaf wrote:
> 
> When/why does this happen? 

Initially, when I use a custom domain builder to create the xenstored
domain without a xenconsoled running yet (as xenconsoled needs xenstore).

> I guess it is because when starting the xenstore domain you cannot use
> xenstore to communicate with xenconsoled (and/or it isn't even running
> yet).
> 
> I wonder if there is a way we can do lazy-setup of the console for just
> the xenstore domain?

Xenstored will produce output on the hypervisor console if Xen is compiled
with debugging. If xenstored produces a lot of output, it can block on
waiting for xenconsoled, which might be blocking on xenstored - so I don't
think we want to hook it up to the console in the normal case, or at least
not the same xenconsoled that talks to domUs.
 
> Alternatively I seem to recall a little tool which Diego wrote to pull
> the console ring out of a domain directly as a debuging aid but that
> relies on us setting up a console ring and evtchn even if xenconsoled
> cannot be involved which makes this patch unnecessary.
> 
> Ian.

This runs into the same blocking problem if xenstored produces too much
output.