Re: [Xen-devel] xl create should refuse to share block devices RW between domains

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Jul 2010, Ian Campbell wrote:
> On Tue, 2010-07-27 at 01:36 +0100, Jeremy Fitzhardinge wrote:
> > When creating a domain, "xl create" should fail if a block device is 
> > shared RW between domains, like xm create does.
> > 
> > I'm not sure how this would be implemented.  Search xenstore for 
> > references to the device when setting up a domain?
> 
> The hotplug scripts have locking and calls to a function called 
> "check_device_sharing" in them, I've been wondering why that wasn't
> kicking in for xl created domains for a little while but never got to
> investigating.
> 
 
those scripts are called by udev and theoretically should work
exactly the same way with xend or libxl.
I didn't test this but I believe that since libxl always uses blktap2,
the script called is block and the codepath taken is the following:

    phys=$(xenstore_read_default "$XENBUS_PATH/physical-device" 'MISSING')
    if [ "$phys" != 'MISSING' ]
    then
      # Depending upon the hotplug configuration, it is possible for this
      # script to be called twice, so just bail.
      exit 0
    fi

so we never do any checks.

I also think that tap_ctl_create is the right place to do these checks,
not a script called by udev after the device has been created.

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