Installation guide

Chapter 22. Additional Information
for IBM System z Users
1. The sysfs File System
The Linux 2.6 kernel introduced the sysfs file system. The sysfs file system is described as a
union of the proc, devfs, and devpty file systems. The sysfs file system enumerates the devices
and busses attached to the system into a file system hierarchy that can be accessed from user
space. It is designed to handle the device and driver specific options that have previously
resided in /proc/, and encompass the dynamic device addition previously offered by devfs.
The sysfs file system is mounted at /sys/ and contains directories that organize the devices at-
tached to the system in several different ways. The /sysfs/ subdirectories include:
1. The /devices/ directory
This directory contains the /css0/ directory. Its subdirectories represent all the subchannels
detected by the Linux kernel. Subchannel directories are named in the form 0.0.nnnn where
nnnn is the subchannel number in hex between 0000 and ffff. Subchannel directories in turn
contain status files and another subdirectory which represents the actual device. The
device directory is named 0.0.xxxx where xxxx is the unit address for the device. The /
devices/ directory also contains status information as well as configuration options for the
device.
2. The /bus/ directory
This contains a /ccw/ subdirectory and a /ccwgroup/ subdirectory. CCW devices are ac-
cessed using channel command words. Devices in the /ccw/ directory only use one
subchannel on the mainframe channel subsystem. CCW group devices are also accessed
with channel command words, but they use more than one subchannel per device. For ex-
ample, a 3390-3 DASD device uses one subchannel, while a QDIO network connection for
an OSA adapter uses three subchannels. The /ccw/ and the /ccwgroup/ directories both
contain directories called devices and drivers:
The /devices/ directory contains a symbolic link to the device directories in the /
sys/devices/css0/ directory.
The /drivers/ directory contains directories for each device driver currently loaded on the
system. Drivers associated with devices such as dasd, console, qeth, and zfcp have direct-
ory entries here. The /driver/ directory contains settings for the device driver, as well as
symbolic links to the devices it is using (in the /sys/devices/css0/ directory).
3. The /class/ directory
This contains directories that group together similar devices such as ttys, SCSI tape drives,
network devices, and other miscellaneous devices.
4. The /block/ directory
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