Announcing the Windows PV Console Driver

It has long been the case that all HVM guests under Xen are provided with a PV console. You can attach to this console in the same way that you attach to the console of a PV guest, by typing in the control domain:

xl console name_of_guest

Until recently there has been no Windows PV driver interaction with this console. Starting with this commit support for logging via the PV console was added to the XENBUS driver.

I’m happy to announce that the three commits to XENBUS starting with this one added the necessary infrastructure to support a brand new XENCONS PV driver which exposes the PV console to Windows user-space as a character device.

The XENCONS driver source is hosted alongside the other PV driver sources on xenbits.xen.org and development builds are available for download here.

The XENCONS package also contains a Windows service to monitor the presence of the PV console device and invoke a command shell login process with redirected stdin/stdout. This means that, once the driver package has been installed, if you attach to the PV console and hit ENTER you’ll see a prompt something like this:

DESKTOP-KVEHAKT login:

From this prompt you can log in as any local user and you’ll then be presented with the command shell:

DESKTOP-KVEHAKT login: User
Password:
Microsoft Windows [Version 10.0.15063]
(c) 2017 Microsoft Corporation. All rights reserved.

C:\Users\User>

Be aware that this shell is running in session 0 so does not have access to the interactive session, but you can still use it for many administrative tasks. For instance, you can run netsh to display aspects of your network configuration:


C:\Users\User>netsh
netsh>interface ipv4 show global
Querying active state...

General Global Parameters
---------------------------------------------
Default Hop Limit : 128 hops
Neighbor Cache Limit : 256 entries per interface
Route Cache Limit : 4096 entries per compartment
Reassembly Limit : 33420160 bytes
ICMP Redirects : enabled
Source Routing Behavior : dontforward
Task Offload : enabled
Dhcp Media Sense : enabled
Media Sense Logging : disabled
MLD Level : all
MLD Version : version3
Multicast Forwarding : disabled
Group Forwarded Fragments : disabled
Randomize Identifiers : enabled
Address Mask Reply : disabled
Minimum Mtu : 576
Locality Address Selection : disabled
Flow Label : disabled

Current Global Statistics
---------------------------------------------
Number of Compartments : 1
Number of NL clients : 7
Number of FL providers : 4

Over the coming weeks I intend to add to the functionality that the driver provides. One obvious extension would be some form of hotkey support to link into the XENBUS_DEBUG interface to enable PV drivers to register a callback to be triggered by a particuler key.

If you are interested in this then please try the XENCONS package and send feedback to the mailing list.

This entry was posted in Announcements, Releases and tagged on by .

About Paul Durrant

I graduated in Computer Science from the University of Cambridge in 1994 and have been working on device drivers and kernels (generally in the networking subsystem) ever since. I spent many years in the Solaris kernel networking group at Sun Microsystems and joined Citrix in 2009 to work on the Windows PV drivers for XenServer.

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