Passthrough support ?

[sanket hase <shase@andrew.cmu.edu>]

Hi ,


I  have been trying to understand PCI -passthrough support.  Please 
correct me if I am wrong in my following inferences.

1. Device emulation and pass through are both implemented using split 
drivers.
2. But, in case of emulation drivers of dom0 are used  where as in case 
of passthrough ( as the name suggests ) native drivers in domU are used .
3. dom0 provides a virtual PCI device { an interface for device-OPs and 
status  of this virtual device} to domU and  through associated event 
channel domU makes
   "synchronous" use of this device.

===
Queries:

1. What i am really not so sure about is ... passthrough case
    Will there be requirement to map the address space of this PCI  
device in domU ?  Will the page which was being shared  so-far 
{xen_pci_sharedinfo}
     for emulation , be "flipped"  ( transferred ) into domU ? 2. Well , 
Having read the code for linux (dom0,domU) I see that there are split  
device  drivers for PCI. (pci front and PCIback). Which are normally
   communicating over xenbus.  which looks almost like other split 
drivers.  How exactly then passthrough enables use of domU's drivers ?
3. And if passthrough support isnt provided how will communication 
between pcifront-pciback  be different ? ( I guess netbsd , freebsd do 
not have passthrough support yet )
4. What  restricts other domUs from accessing PCI device given to other 
domU via passrthrough support.


Regards,
Sanket