Red Hat Enterprise Linux Installation Guide 5.2 - linux.meuhobby.com

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
attached 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
accessed 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
example, 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
directory 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.
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