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Re: [Xen-devel] About block device mapping for guests

> It's technically possible to make the frontend behave more like a CD
> drive, it's just that there's not a lot of demand for this, so it's
> not implemented.

Right, understood. Seems like this need would be better served by
being able to give entire IDE/SCSI devices to some guests, so they can
run all the IDE/SCSI commands they will ever need.

I guess you could do that but we'd need back / frontend drives that carried IDE / SCSI commands between guests and domain 0.

If you really want to give a whole device to a guest or make a CD writer work you could: * give the domain a whole PCI SCSI / IDE / USB controller and plug the device into that * export a USB drive to the domain with USB virtualisation

I assume this specifically means that guest domains will not have the
block devices created by devfs at all - but if one were to manually
create the block devices with the correct major and minor, it would

Yes, that should work.

Hmm. How will the devices be named under sysfs? If I just specify a
major and minor device number, where does Xen dig up the name it
should be registered under? And how does udev pick the right name for
the actual device file?

First off, Xen doesn't know / care about the devices at all - it's the drivers in XenLinux that take care of that.

The guest operating system (e.g. XenLinux) will bind the major / minor to a name according to it's own policy. e.g. under Linux 0x801 is conventionally /dev/sda1 so unless you have a weird setup, that's what it'll appear as. I guess the files appear under SysFS similarly to how devices with the same major / minor would under vanilla Linux.

Udev knows the right name for the device file according to its own policy setup.

Immensely. Now I know why none of my domains ever manage to find a
root device ;-)

Ahh good ;-)


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