Re: [Xen-devel] [PATCH v4 3/5] libxl: add support for vscsi

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Apr 22, 2015 at 10:08:52AM +0200, Olaf Hering wrote:
> On Tue, Apr 21, Konrad Rzeszutek Wilk wrote:
> 
> > On Fri, Apr 17, 2015 at 08:30:58AM +0000, Olaf Hering wrote:
> > > +=item B<vscsi=[ "VSCSI_SPEC_STRING", "VSCSI_SPEC_STRING", ...]>
> > > +
> > > +Specifies the PVSCSI devices to be provided to the guest. PVSCSI passes
> > > +dom0 SCSI devices as-is to the guest.
> > s/dom0/backend/
> 
> I will make that change.
> 
> > As in theory you could run an HVM guest with an SCSI device passed in - and
> > use said backed to pass the SCSI device to another guest.
> 
> Sounds interesting. I assume you meant "backend"? How will the domU talk

Yes, backend.
> to the other domU? Not sure if my libxl change covers that use case, and

Using the ring-buffer? Communicate via the Xenstore?

> how I would be able to verify such functionality. Hopefully merging my
> series will not depend on such use case.

Right, not dependent on it.
> 
> > 'as-is' ? I thought there were some filtering done in the backend?
> 
> Perhaps 'passthrough with filtering'? I will remove it.
> 
> > > +Each VSCSI_SPEC_STRING consists of "pdev,vdev[,options]".
> > > +'pdev' describes the physical device, preferable in a persistant format.
> > What is 'persistent' format?
> 
> Anything that uses identifiers provided by the hardware, like serial
> numbers. /dev/disk/by-*/* for example. The h:c:t:l notation is not
> persistant because the "h" part will change across reboots.

You might want to define what you mean by that. Or include the
example (/dev/disk/by-*/*).
> 
> > > +
> > > +=item C<option>
> > > +
> > > +No options recognized.
> > > +
> > > +=back
> > > +
> > > +=item B<Linux xenlinux>
> > xenlinux? Classic Xen?
> 
> Anything based on linux-2.6.18-xen.hg. I will adjust this to "Linux
> based on classic xen kernel"

Excellent!
> 
> > > +static int libxl__device_vscsi_new_backend(libxl__egc *egc,
> > > +                                           libxl__ao_device *aodev,
> > > +                                           libxl_device_vscsi *vscsi,
> > > +                                           libxl_domain_config *d_config)
> > > +{
> 
> > > +        rc = libxl__device_vscsi_dev_backend_set(gc, v, back);
> > > +        if (rc) goto out;
> > Don't you want 'return rc' as the out will try to call 
> > libxl__xs_transaction_abort?
> 
> The current code works because t is initialized to XBT_NULL, and
> libxl__xs_transaction_abort will do nothing in that case. I will adjust
> this as you suggested.

Thanks.
> 
> Olaf

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