Re: [Xen-devel] [PATCH 3/4] libxl: only allow guests with a device model to use cd-{eject/insert}

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, 8 Apr 2016, Wei Liu wrote:
> On Fri, Apr 08, 2016 at 04:17:55PM +0200, Roger Pau Monné wrote:
> > On Fri, 8 Apr 2016, Wei Liu wrote:
> > > On Thu, Apr 07, 2016 at 07:45:28PM +0200, Roger Pau Monne wrote:
> > > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > > > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > > ---
> > > >  tools/libxl/libxl.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> > > > index 9d785a4..232e2c1 100644
> > > > --- a/tools/libxl/libxl.c
> > > > +++ b/tools/libxl/libxl.c
> > > > @@ -2909,6 +2909,12 @@ int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t 
> > > > domid, libxl_device_disk *disk,
> > > >          goto out;
> > > >      }
> > > >  
> > > > +    if (dm_ver == LIBXL_DEVICE_MODEL_VERSION_NONE) {
> > > > +        LOG(ERROR, "HVM guests without a device model cannot use 
> > > > cd-insert");
> > > 
> > > It's not specific to HVM, right?
> > 
> > It's specific to guests with a device model (those are the only ones that 
> > can have an emulated CDROM device), and the only guests that can have a 
> > device model are HVM (although not all of them).
> > 
> 
> Remind me again: how does PV guest CDROM work? ISTR it will also go
> through this function? My memory is vague though...

No, AFAICT PV guests use block-attach/detach in order to manage CDROMs, 
the usage of the cd-eject/insert commands is already limited to HVM 
guests, my check is only further limiting it to HVM guests with a device 
model (so it's not used for PVH guests).

A little above of the check that I've added:

    libxl_domain_type type = libxl__domain_type(gc, domid);
    if (type == LIBXL_DOMAIN_TYPE_INVALID) {
        rc = ERROR_FAIL;
        goto out;
    }
    if (type != LIBXL_DOMAIN_TYPE_HVM) {
        LOG(ERROR, "cdrom-insert requires an HVM domain");
        rc = ERROR_INVAL;
        goto out;
    }

Roger.

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