Listing devices with lscss

Ubuntu 22.04 LTS KVM guest

The particulars of the channel subsystem view of a guest become visible when you list devices with lscss.

Example

# lscss
Device   Subchan. DevType CU Type Use PIM PAM POM CHPIDs
----------------------------------------------------------------------
0.0.0042 0.0.0000 0000/00 3832/01 yes 80  80  ff  00000000 00000000
0.0.0815 0.0.0001 0000/00 3832/02 yes 80  80  ff  00000000 00000000
0.0.9999 0.0.0002 0000/00 3832/03 yes 80  80  ff  00000000 00000000
0.1.abcd 0.1.0000 0000/00 3832/05 yes 80  80  ff  00000000 00000000
...
0.1.6196 0.1.36e2 3390/0c 3990/e9 yes fc  fc  ff  32333435 40410000
...

As illustrated in the example, the output, typically, shows numerous paravirtualized CCW devices. The output columns DevType, PIM, PAM, POM, and CHPIDs show identical values for these devices. These values result from the virtualization and carry no information that is characteristic for a particular device.

The output of the example also includes a pass-through DASD, with device type 3390/0c, for which all fields provide device-characteristic information.

The following columns contain meaningful device information for paravirtualized CCW devices:

Device

is the device bus-ID that uniquely identifies a device to the guest and to the KVM hypervisor.

Use device bus-IDs to identify devices to the KVM hypervisor administrator. The KVM hypervisor defines these bus-IDs with prefix fe instead of 0. For example, 0.0.0042 on the guest is specified as fe.0.0042 in the virtual server configuration on the KVM hypervisor.

Device bus-IDs are persistent across reboots and change only if the device definitions are changed in the KVM hypervisor.

Subchan.

shows the current assignment of a subchannel to the device.

In contrast to the persistent device bus-IDs, subchannel assignments to devices might change across reboots or as a result of hotplug events.

CU Type

has a two-digit suffix that identifies the device type.

For example, 01 in 3832/01 identifies a network device and 02 in 3832/02 identifies a block device.

Use

indicates whether the device is online.