On 6/11/2013 11:36 AM, George Dunlap wrote:

On 06/10/2013 10:06 PM, Konrad Rzeszutek Wilk wrote:

quoted

There are two tool-stack that can instruct the Xen PCI frontend
and backend to change states: 'xm' (Python code with a daemon),
and 'xl' (C library - does not keep state changes).

With the 'xm', the path to disconnect a PCI device (xm pci-detach
<guest> <BDF>)is:

4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 
4(Connected)->5(Closing*).

The * is for states that the tool-stack sets. For 'xl', it is similar:

4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 4(Connected)

Both of them also tear down the XenBus structure, so the backend
state ends up going in the 3(Initialised) and calls 
pcifront_xenbus_remove.

So I looked a little bit into this; there are actually two different 
states that happen as part of this handshake.  In order to disonnect a 
*device*, xl signals using the *bus* state, like this:
* Wait for the *bus* to be in state 4(Connected)
* Set the *device* state to 5(Closing)
* Set the *bus* state to 7(Reconfiguring)
* Wait for the *bus* state to return to 4(Connected)

So are all of these states you see the *bus* state?  And why would you 
disconnect the whole pci bus if you're only removing one device?

Correct. The stats I enumerated are *bus* states. Not per-device states.
I presume (and I hadn't checked xm) that Xend has some logic to only 
disconnect the bus if all of the PCI devices have been disconnected. In 
'xl' it does not do that.

The testing I did was just with one PCI device.

 -George