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[Xen-devel] [PATCH PV_OPS] pciback support

This is back-port (up-port?) of the pci-back driver from the 2.6.18.hg tree.
The driver is quite similar to the pci-stub, excep that is intended for
paravirtualized guests. This driver works in conjunction with the pci-front
(frontend driver) to exchange PCI write/read to the configuration space and
to have the BARs mapped properly for the guest.

The usage of this is, as said, is similar to pci-stub:
lspci | grep SCSI
01:14.0 SCSI storage controller: Adaptec AHA-2940U/UW/D / AIC-7881U
echo "0000:01:14.0" > /sys/bus/pci/drivers/aic94xx/unbind
echo "0000:01:14.0" > /sys/bus/pci/drivers/pciback/new-slot
echo "0000:01:14.0" > /sys/bus/pci/drivers/aic94xx/bind

and add this entry:

pci = [ '0000:01.14.0' ]

in your .xm file.

The PV guest, if it has the PCI frontend, should now see the PCI device.
I've tested this succesfully with a SLES10 PV guest with a couple of devices.

But please be beware of this warning if it shows up:
(XEN) irq.c:1113:d1 Cannot bind IRQ 17 to guest. Others do not share.

On my machine it lead to Dom0 deciding that a spurrious interrupt kicked off
and it disabled the IRQ. The end result was that other devices on the same
interrupt line stopped working. I am not yet certain how to make this work
properly (whether to check if the PCI device in question interrupt line is
being shared beforehand by xm?, or do something in Xen?).

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