Creating a CTCM group device

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest

Use the group attribute to create a CTCM group device.

Before you begin

You must know the device bus-IDs that correspond to the local read and write subchannel of your CTCM connection as defined in your IOCDS.

Procedure

To define a CTCM group device, write the device bus-IDs of the subchannel pair to /sys/bus/ccwgroup/drivers/ctcm/group.

Issue a command of this form:

# echo <read_device_bus_id>,<write_device_bus_id> > /sys/bus/ccwgroup/drivers/ctcm/group

Results

The CTCM device driver uses the device bus-ID of the read subchannel to create a directory for a group device:

/sys/bus/ccwgroup/drivers/ctcm/<read_device_bus_id>

This directory contains a number of attributes that determine the settings of the CTCM group device.

Example

Assuming that device bus-ID 0.0.2000 corresponds to a read subchannel:

# echo 0.0.2000,0.0.2001 > /sys/bus/ccwgroup/drivers/ctcm/group

This command results in the creation of the following directories in sysfs:

/sys/bus/ccwgroup/drivers/ctcm/0.0.2000
/sys/bus/ccwgroup/devices/0.0.2000
/sys/devices/ctcm/0.0.2000

Note: When the device subchannels are added, device types 3088/08 and 3088/1f can be assigned to either the CTCM or the LCS device driver.

To check which devices are assigned to which device driver, issue the following commands:

# ls -l /sys/bus/ccw/drivers/ctcm
# ls -l /sys/bus/ccw/drivers/lcs

To change a faulty assignment, use the unbind and bind attributes of the device. For example, to change the assignment for device bus-IDs 0.0.2000 and 0.0.2001 issue the following commands:

# echo 0.0.2000 > /sys/bus/ccw/drivers/lcs/unbind
# echo 0.0.2000 > /sys/bus/ccw/drivers/ctcm/bind
# echo 0.0.2001 > /sys/bus/ccw/drivers/lcs/unbind
# echo 0.0.2001 > /sys/bus/ccw/drivers/ctcm/bind