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+S/390 common I/O-Layer - command line parameters and /proc entries
+==================================================================
+
+Command line parameters
+-----------------------
+
+* cio_msg = yes | no
+  
+  Determines whether information on found devices and sensed device 
+  characteristics should be shown during startup, i. e. messages of the types 
+  "Detected device 0.0.4711 on subchannel 0.0.0042" and "SenseID: Device
+  0.0.4711 reports: ...".
+
+  Default is off.
+
+
+* cio_ignore = {all} |
+	       {<device> | <range of devices>} |
+	       {!<device> | !<range of devices>}
+
+  The given devices will be ignored by the common I/O-layer; no detection
+  and device sensing will be done on any of those devices. The subchannel to 
+  which the device in question is attached will be treated as if no device was
+  attached.
+
+  An ignored device can be un-ignored later; see the "/proc entries"-section for
+  details.
+
+  The devices must be given either as bus ids (0.0.abcd) or as hexadecimal
+  device numbers (0xabcd or abcd, for 2.4 backward compatibility).
+  You can use the 'all' keyword to ignore all devices.
+  The '!' operator will cause the I/O-layer to _not_ ignore a device.
+  The order on the command line is not important.
+
+  For example, 
+	cio_ignore=0.0.0023-0.0.0042,0.0.4711
+  will ignore all devices ranging from 0.0.0023 to 0.0.0042 and the device
+  0.0.4711, if detected.
+  As another example,
+	cio_ignore=all,!0.0.4711,!0.0.fd00-0.0.fd02
+  will ignore all devices but 0.0.4711, 0.0.fd00, 0.0.fd01, 0.0.fd02.
+
+  By default, no devices are ignored.
+
+
+/proc entries
+-------------
+
+* /proc/cio_ignore
+
+  Lists the ranges of devices (by bus id) which are ignored by common I/O.
+
+  You can un-ignore certain or all devices by piping to /proc/cio_ignore. 
+  "free all" will un-ignore all ignored devices, 
+  "free <device range>, <device range>, ..." will un-ignore the specified
+  devices.
+
+  For example, if devices 0.0.0023 to 0.0.0042 and 0.0.4711 are ignored,
+  - echo free 0.0.0030-0.0.0032 > /proc/cio_ignore
+    will un-ignore devices 0.0.0030 to 0.0.0032 and will leave devices 0.0.0023
+    to 0.0.002f, 0.0.0033 to 0.0.0042 and 0.0.4711 ignored;
+  - echo free 0.0.0041 > /proc/cio_ignore will furthermore un-ignore device
+    0.0.0041;
+  - echo free all > /proc/cio_ignore will un-ignore all remaining ignored 
+    devices.
+
+  When a device is un-ignored, device recognition and sensing is performed and 
+  the device driver will be notified if possible, so the device will become
+  available to the system.
+
+  You can also add ranges of devices to be ignored by piping to 
+  /proc/cio_ignore; "add <device range>, <device range>, ..." will ignore the
+  specified devices.
+
+  Note: Already known devices cannot be ignored.
+
+  For example, if device 0.0.abcd is already known and all other devices
+  0.0.a000-0.0.afff are not known,
+	"echo add 0.0.a000-0.0.accc, 0.0.af00-0.0.afff > /proc/cio_ignore"
+  will add 0.0.a000-0.0.abcc, 0.0.abce-0.0.accc and 0.0.af00-0.0.afff to the
+  list of ignored devices and skip 0.0.abcd.
+
+  The devices can be specified either by bus id (0.0.abcd) or, for 2.4 backward
+  compatibilty, by the device number in hexadecimal (0xabcd or abcd).
+
+
+* /proc/s390dbf/cio_*/ (S/390 debug feature)
+
+  Some views generated by the debug feature to hold various debug outputs.
+
+  - /proc/s390dbf/cio_crw/sprintf
+    Messages from the processing of pending channel report words (machine check
+    handling), which will also show when CONFIG_DEBUG_CRW is defined.
+
+  - /proc/s390dbf/cio_msg/sprintf
+    Various debug messages from the common I/O-layer; generally, messages which 
+    will also show when CONFIG_DEBUG_IO is defined.
+
+  - /proc/s390dbf/cio_trace/hex_ascii
+    Logs the calling of functions in the common I/O-layer and, if applicable, 
+    which subchannel they were called for.
+
+  The level of logging can be changed to be more or less verbose by piping to 
+  /proc/s390dbf/cio_*/level a number between 0 and 6; see the documentation on
+  the S/390 debug feature (Documentation/s390/s390dbf.txt) for details.
+
+* For some of the information present in the /proc filesystem in 2.4 (namely,
+  /proc/subchannels and /proc/chpids), see driver-model.txt.
+  Information formerly in /proc/irq_count is now in /proc/interrupts.