From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Smith Subject: Re: [Xen-tools] [PATCH] Clean up dom_get() usage Date: Fri, 16 Sep 2005 13:57:09 -0700 Message-ID: <874q8kivdm.fsf@us.ibm.com> References: <87irx2xnf3.fsf@us.ibm.com> <3d8eece20509161222782a9051@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Christian.Limpach@cl.cam.ac.uk Cc: Xen Tools Developers , Xen Developers List-Id: xen-devel@lists.xenproject.org CL> I don't think the 3rd hunk is needed. The temporary variable is a added so that we can verify that dom_get() returned non-None. A failure to get the current domain's info from xc (which could happen) would result in an "unsubscriptable object" exception in a less-than-obvious place while xend is starting up. Am I missing something? CL> It would make more sense to have a patch which replaces the magic CL> dom0 domid by a global variable indicating the domid of the domain CL> where xend is running. The domid in this case isn't magic though, is it? We just use the domid that is passed to us, which I think we assume is correctly set to the privileged domain's ID. Although the temporary variable is definitely not indicative of this fact :) CL> It's possibly a sensible behaviour, but I'd like to move away from CL> code which does stuff as a side effect. We don't want to end up CL> with countless places doing random actions just because they CL> happen to notice a state change first. I see your point. However, I do feel that we should be informative and defensive where possible. I think that no matter where it is detected, the hypervisor reporting a domain is no longer present should not be ignored. Very recently, there have been very strange problems occurring due to stale state that gets left around. Would it be appropriate to take an action based on what state we think we're in? For example, if we were running, mark ourselves as "crashed"; if we were shutting down, remove ourselves from the list. -- Dan Smith IBM Linux Technology Center Open Hypervisor Team email: danms@us.ibm.com