Re: [Xen-devel] [RFC] [PATCH] [XEN] [ACM] Enable updating policy on running system

[Stefan Berger <stefanb@xxxxxxxxxx>]

Keir Fraser <keir@xxxxxxxxxxxxx> wrote on 04/20/2007
12:46:40 PM:

> On 20/4/07 17:02, "Stefan Berger" <stefanb@xxxxxxxxxx>
wrote:

> > 
> > Anyway, in response to your main question, I wonder what you
actually need
> > to serialise against? Is it sufficient to just sync against domain
creation
> > -- what if event channels or grant mappings are also occurring
during the
> > policy change? Is there some specific part of domain creation
you need to
> > serialise against? 
> 
> While the policy update is happening, a domain could be created with
> a label that is about to be modified or even deleted as part of the
> policy update. 
> 
> When a label is associated with a domain, doesn’t that call into
ACM
> code? In which case you could define your own locking against that
event.

Actually the easiest solution would be to grab the
read-lock of the acm policy in do_domctl() before acm_pre_domctl() and
release it after acm_post_domctl() or acm_fail_domctl(), which are both
at the end of do_domctl(). All of these functions grab and release the
read lock individually in some subfunction, but the lock is not being held
permanently which is what bothers me for the update.  

   Stefan

> 
>  -- Keir
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