Re: [Xen-devel] [PATCH 4 of 7] [OCAML] Fix a problem with ocaml xenstored

[Jonathan Ludlam <Jonathan.Ludlam@xxxxxxxxxxxxx>]

On 30 Sep 2011, at 13:50, Ian Campbell wrote:

> 
> On Fri, 2011-09-30 at 13:22 +0100, Jonathan Ludlam wrote:
>> Ah, that's a shame. I was hoping this was a bugfix to the ocaml
>> xenstored and that the C version already did this. Unfortunately the
>> patch here went in to XenServer a couple of years ago, and Thomas, who
>> made the change, has since left. I'll dig into this and see why we
>> depend upon it. 
> 
> Seems to be CA-30927 which was "internal shutdown doesn't work anymore
> after VM.checkpoint":
> 
>        The bugs comes from the fact that xal always assume that
>        suspended domains are or will be soon dead.
> 
>        However, for VM.checkpoint that assumptions is false, as the VM
>        is suspended, snapshoted, and then resumed, without destroying
>        the domain.
> 
> Thomas said in that ticket:
> 
>        I fixed this issue by:
>              * teach to xal how to handle dead domains for suspended
>                reasons which become suddenly alive
>              * when resuming a domain, use the xenstore introduce call
>              * modify xenstore to generates a @introduceDomain event
>                even if the introduced domain does not exists
> 
>        I believe nobody care to see too many @introduceDomain event, so
>        that will not change anything. My fix modifies the code path
>        taken by VM.suspend, but that should be safe because xapi
>        destroys properly the domain after suspending it.
> 
> (I think he meant _does_ exist in the third bullet). In his commit
> message he said:
> 
>        Teach xal what to do with dead domains which become alive again.
> 
>        Needed to modify xenstored as well in order to trigger a
>        @introduceDomain event even if the introduce call tries to
>        introduce an already existing domain. That will kick-up xal in
>        case when resuming the domain.
> 
> I think possibly the right fix would have been to have xal kick-up
> itself. That said spurious @introduceDomain watches are pretty harmless
> (as he suggests) since they have no context, the recipient has to go and
> check it's idea of the world vs the real state to know what happened an
> the answer "nothing" is not a big deal...
> 

I think you're right that the fix should go into xal. Please don't commit this 
particular patch; we'll keep it in our patch queue until we can fix it properly 
in xapi.

Jon


> Ian.
> 
> 
>> 
>> Jon
>> 
>> On 30 Sep 2011, at 08:49, Ian Campbell wrote:
>> 
>>> On Thu, 2011-09-29 at 22:17 +0100, Jon Ludlam wrote:
>>>> Have xenstored trigger an @introduceDomain event even if the
>>>> introduce call tries to introduce an already existing domain.
>>> 
>>> The C daemon doesn't appear to behave this way. It would be nice to
>>> explain why this change is necessary. 
>>> 
>>>> Signed-off-by: Thomas Gazagnaire <thomas@xxxxxxxxxxxx>
>>>> Acked-by: Jon Ludlam <jonathan.ludlam@xxxxxxxxxxxxx>
>>>> 
>>>> diff -r 734cb0807357 -r b6022a18ebb0 tools/ocaml/xenstored/process.ml
>>>> --- a/tools/ocaml/xenstored/process.ml
>>>> +++ b/tools/ocaml/xenstored/process.ml
>>>> @@ -168,9 +168,10 @@
>>>>            | _                         -> raise Invalid_Cmd_Args;
>>>>            in
>>>>    let dom =
>>>> -          if Domains.exist domains domid then
>>>> +          if Domains.exist domains domid then begin
>>>> +                  Connections.fire_spec_watches cons "@introduceDomain";
>>>>                    Domains.find domains domid
>>>> -          else try
>>>> +          end else try
>>>>                    let ndom = Xc.with_intf (fun xc ->
>>>>                            Domains.create xc domains domid mfn port) in
>>>>                    Connections.add_domain cons ndom;
>>>> 
>>>> _______________________________________________
>>>> Xen-devel mailing list
>>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>>> http://lists.xensource.com/xen-devel
>>> 
>>> 
>> 
> 
> 


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