* Daniel P. Berrange (berrange@xxxxxxxxxx) wrote:
> On Tue, May 06, 2008 at 01:36:05PM -0400, Chris Lalancette wrote:
> > All,
> > We've had a number of requests to increase the number of xvd devices
> > that a
> > PV guest can have. Currently, if you try to connect > 16 disks, you get an
> > error from xend. The problem ends up being that both xend and blkfront
> > assume
> > that for dev_t, major/minor is 8 bits each, where in fact there are
> > actually 10
> > bits for major and 22 bits for minor.
Just a nit, it's actually 12:20.
> > Therefore, it shouldn't really be a problem giving lots of disks to
> > guests.
> > The problem is in backwards compatibility, and the details. What I am
> > initially proposing to do is to leave things where they are for
> > /dev/xvd[a-p];
> > that is, still put the xenstore entries in the same place, and use 8 bits
> > for
> > the major and 8 bits for the minor. For anything above that, we would end
> > up
> > putting the xenstore entry in a different place, and pushing the major into
> > the
> > top 10 bits (leaving the bottom 22 bits for the minor); that way old guests
> > won't fire when the entry is added, and we will add code to newer guests
> > blkfront so that they will fire when they see that entry. Does anyone see
> > any
> > problems with this setup, or have any ideas how to do it better?
>
> Putting the xenstore entries in a different place is a non-starter. Too
> many things look at that location already. When blktap was added and it
> put xenstore entries in a different place it took months to track down
> all the bugs this caused.
I'm not sure what you mean? Since this is blkfront it'd be more like
adding a virtual-device2 to extend the protocol.
/* FIXME: Use dynamic device id if this is not set. */
err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device", "%i", &vdevice);
if (err != 1) {
xenbus_dev_fatal(dev, err, "reading virtual-device");
return err;
}
IOW smth simple like:
err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device", "%i", &vdevice);
if (err == -ENOENT)
err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device2", "%i",
&vdevice);
Then we can stop propagating the myth that dev_t is 8:8.
thanks,
-chris
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
Home