Monday, September 11, 2017

DataCenter Insider Article

See here for an article (in German) in DataCenter Insider about KVM on z's history, usage concepts, support and z14 features.

Tuesday, September 5, 2017

QEMU v2.10 released

QEMU v2.10 is out. See here for a detailed list of all changes related to IBM Z. Here are some of the highlights from a KVM on z perspective:
  • z14 CPU model
    Provides base support for all of the features introduced with the z14's new processor generation.
    See this previous blog post for details.
  • Emulated 3270 Device
    This implementation has been tested with x3270 only. Your mileage with other clients might vary. For practical matters, the sclp console remains to be the recommended terminal type for KVM guests on Z.
    As this feature is still marked as experimental in QEMU, there is currently no libvirt support available. Therefore to configure a 3270 device on a guest (accessible on all IP addresses of the host at port 23), we must use libvirt’s ability to pass-through arbitrary QEMU command line arguments via domain XML (see here for furher details):
    <domain type='kvm' xmlns:qemu=''>
        <qemu:arg value="-chardev"/>
        <qemu:arg value="socket,id=charconsole1,host=,port=23,\
        <qemu:arg value="-device"/>
        <qemu:arg value="x-terminal3270,chardev=charconsole1,\

    See here for further hints on how to use.
  • Bootparameter Support
    Until now, when a guest had multiple kernels to boot with, one had to change the default kernel in /etc/zipl.conf and re-run zipl to boot with a different kernel next time.
    With this feature, we now support option -L in the chreipl command from the s390-tools package, which allows to switch to a different boot option dynamically, e.g. using
  • $ chreipl ccw -d 0.0.1234 -L 2
    However, if somebody has set a new default kernel that does not boot, this will not help, since the guest will not start anymore in the first place.
    However, with the newly introduced attribute loadparm, one can switch to a different (working) kernel within the host in a guest's XML:
    <boot order='1' loadparm='2'>
    • chreipl changes will no longer be effective after the respective guest has been powered off.
    • The loadparm attribute became available with libvirt v3.5 or higher.