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Re: [Libvir] PATCH 2/2: Support QEMU (+KVM) in libvirt



On Tue, Jan 09, 2007 at 09:44:44AM -0500, Daniel Veillard wrote:
> On Fri, Jan 05, 2007 at 09:18:53PM +0000, Daniel P. Berrange wrote:
> > The attached patch provides a new driver backend for libvirt which allows
> > management of QEMU instances by talking to the libvirt QEMU daemon. It
> > basically just marshalls libvirt API calls onto the wire & de-marshalls
> > the reply. All the interesting functionality stuff is in the daemon.
> 
>   Okay, but I'm getting a bit lost about the potential daemons running,
> there one can be autostarted, in the previous patch we also potentially
> fork(fork(daemon)) so I'm wondering how many process are actually running
> in the end, maybe I will need a couple of pictures, like in the current
> architecture page http://libvirt.org/architecture.html (which will have
> to be updated too :-)

There's two ways its launched:

 - The session bus is auto-launched by libvirt. In this scenaro, libvirt
   does the double fork() magic to dis-inherit the libvirt_qemud process
 - The system bus is started manually. In this case, it runs in foreground
   unless you use the --daemon command line argument to make it do the
   double-fork() into background.

> [...]
> > +int qemudNodeGetInfo(virConnectPtr conn ATTRIBUTE_UNUSED,
> > +                     virNodeInfoPtr info){
> > +    info->cores = 1;
> > +    info->threads = 1;
> > +    info->sockets = 1;
> > +    info->nodes = 1;
> > +    strcpy(info->model, "i686");
> > +    info->mhz = 6000;
> > +    info->cpus = 1;
> > +    info->memory = 1024*1024;
> > +    return 0;
> > +}
> 
>   haha :-) At least worth a big TODO !
> 
> Shouldn't qemud_internal.c gets its own error reporting function like the
> other _internal.c which does the right stuff, I only spotted returns of
> error values, and this is linked to the client binary so this seems to be
> missing, right ?

The only errors that should be occurring in qemud_internal.c are two
classes:

  - Data transport errors (eg, failure to connect, TLS failures, etc)
  - Errors forwarded back from the daemon over the wire.

I already deal with the latter. The former probably needs a little more
work.

> > RCS file: /data/cvs/libvirt/src/virsh.c,v
> > retrieving revision 1.41
> > diff -u -p -r1.41 virsh.c
> > --- src/virsh.c	22 Nov 2006 17:48:29 -0000	1.41
> > +++ src/virsh.c	5 Jan 2007 21:09:08 -0000
> > @@ -292,7 +292,7 @@ cmdConnect(vshControl * ctl, vshCmd * cm
> >      
> >      if (ctl->name)
> >          free(ctl->name);
> > -    ctl->name = vshCommandOptString(cmd, "name", NULL);
> > +    ctl->name = vshStrdup(ctl, vshCommandOptString(cmd, "name", NULL));
> >  
>   I'm a bit lost on that one, was that a separate bug ? 
> We switch from a static string to dynamically allocated one, right ?

Opps, this is compeltely unrelated to QEMU - its a general bug. The string
from vshCommandOptString is just a pointer to its internal buffer. This
is free'd next time user enters a command in virsh. So by storing it in
ctl->name we keep a pointer to a free'd string, with predictable SEGV
a short while later. Simply dup'ing the string is enough.

> > @@ -268,6 +268,9 @@ virDefaultErrorFunc(virErrorPtr err)
> >          case VIR_FROM_RPC:
> >              dom = "XML-RPC ";
> >              break;
> > +        case VIR_FROM_QEMUD:
> > +            dom = "QEMUD ";
> > +            break;
> >      }
> >      if ((err->dom != NULL) && (err->code != VIR_ERR_INVALID_DOMAIN)) {
> >          domain = err->dom->name;
> 
>   I guess some new error code will need to be added too once quemud_internal.c
> is being updated ... Hum, how do we process errors provided by the server ?

The libvirt_qemud  daemon includes <libvirt/virterror.h> and sends back the
appropriate error codes over the wire, along with a message. This is used
to call  __virRaiseError  - see the qemudPacketError()  function at the top
of the qemud_internal.c file - this function is called whenver the wire
protocol gives back an unexpected result

Dan.
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