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Re: [PATCH 2/2] xen-pciback: prepare for the split for stub and PV

On 23.09.21 11:02, Oleksandr Andrushchenko wrote:

On 23.09.21 00:10, Stefano Stabellini wrote:
On Wed, 22 Sep 2021, Oleksandr Andrushchenko wrote:
--- a/drivers/xen/xen-pciback/xenbus.c
+++ b/drivers/xen/xen-pciback/xenbus.c
@@ -743,6 +743,9 @@ const struct xen_pcibk_backend *__read_mostly 
int __init xen_pcibk_xenbus_register(void)
+       if (!xen_pcibk_pv_support())
+               return 0;
Is this truly enough to stop the PV backend from initializing? Have you
actually tested it to make sure? If it works, amazing! I am quite happy
about this approach :-)

Well, I put some logs into the driver and saw nothing obvious pointing

to any backend activities (probably this is also because I don't have any

frontend). I see that the xenbus driver is not registered. In XenStore I see:

root@dom0:~# xenstore-ls -f | grep pci
/local/domain/0/backend/pci = ""
/local/domain/0/backend/pci/2 = ""
/local/domain/0/backend/pci/2/0 = ""
/local/domain/0/backend/pci/2/0/frontend = "/local/domain/2/device/pci/0"
/local/domain/0/backend/pci/2/0/frontend-id = "2"
/local/domain/0/backend/pci/2/0/online = "1"
/local/domain/0/backend/pci/2/0/state = "1"
/local/domain/0/backend/pci/2/0/domain = "DomU"
/local/domain/0/backend/pci/2/0/key-0 = "0000:03:00.0"
/local/domain/0/backend/pci/2/0/dev-0 = "0000:03:00.0"
/local/domain/0/backend/pci/2/0/opts-0 = 
/local/domain/0/backend/pci/2/0/state-0 = "1"
/local/domain/0/backend/pci/2/0/num_devs = "1"
/local/domain/2/device/pci = ""
/local/domain/2/device/pci/0 = ""
/local/domain/2/device/pci/0/backend = "/local/domain/0/backend/pci/2/0"
/local/domain/2/device/pci/0/backend-id = "0"
/local/domain/2/device/pci/0/state = "1"
/libxl/pci = ""
/libxl/pci/0000-03-00-0 = ""
/libxl/pci/0000-03-00-0/domid = "2"

But IIUIC these come from the toolstack

@Juergen, do you know how to check if the backend is indeed not running

or the above should be enough to prove?

I don't see how the backend could be running without being registered
with xenbus. It won't receive any watches, so there is no way a
connection with a frontend could be established.


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