dc06010c62
Update documentation of the common I/O layer: - Add MSS-specific example. - Add more information on ccwgroup devices. - Add channel path type attribute. - Fix typo. Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
278 lines
9.4 KiB
Plaintext
278 lines
9.4 KiB
Plaintext
S/390 driver model interfaces
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-----------------------------
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1. CCW devices
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--------------
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All devices which can be addressed by means of ccws are called 'CCW devices' -
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even if they aren't actually driven by ccws.
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All ccw devices are accessed via a subchannel, this is reflected in the
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structures under devices/:
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devices/
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- system/
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- css0/
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- 0.0.0000/0.0.0815/
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- 0.0.0001/0.0.4711/
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- 0.0.0002/
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- 0.1.0000/0.1.1234/
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...
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In this example, device 0815 is accessed via subchannel 0 in subchannel set 0,
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device 4711 via subchannel 1 in subchannel set 0, and subchannel 2 is a non-I/O
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subchannel. Device 1234 is accessed via subchannel 0 in subchannel set 1.
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You should address a ccw device via its bus id (e.g. 0.0.4711); the device can
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be found under bus/ccw/devices/.
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All ccw devices export some data via sysfs.
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cutype: The control unit type / model.
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devtype: The device type / model, if applicable.
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availability: Can be 'good' or 'boxed'; 'no path' or 'no device' for
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disconnected devices.
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online: An interface to set the device online and offline.
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In the special case of the device being disconnected (see the
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notify function under 1.2), piping 0 to online will forcibly delete
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the device.
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The device drivers can add entries to export per-device data and interfaces.
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There is also some data exported on a per-subchannel basis (see under
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bus/css/devices/):
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chpids: Via which chpids the device is connected.
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pimpampom: The path installed, path available and path operational masks.
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There also might be additional data, for example for block devices.
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1.1 Bringing up a ccw device
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----------------------------
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This is done in several steps.
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a. Each driver can provide one or more parameter interfaces where parameters can
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be specified. These interfaces are also in the driver's responsibility.
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b. After a. has been performed, if necessary, the device is finally brought up
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via the 'online' interface.
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1.2 Writing a driver for ccw devices
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------------------------------------
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The basic struct ccw_device and struct ccw_driver data structures can be found
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under include/asm/ccwdev.h.
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struct ccw_device {
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spinlock_t *ccwlock;
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struct ccw_device_private *private;
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struct ccw_device_id id;
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struct ccw_driver *drv;
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struct device dev;
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int online;
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void (*handler) (struct ccw_device *dev, unsigned long intparm,
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struct irb *irb);
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};
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struct ccw_driver {
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struct module *owner;
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struct ccw_device_id *ids;
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int (*probe) (struct ccw_device *);
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int (*remove) (struct ccw_device *);
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int (*set_online) (struct ccw_device *);
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int (*set_offline) (struct ccw_device *);
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int (*notify) (struct ccw_device *, int);
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struct device_driver driver;
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char *name;
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};
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The 'private' field contains data needed for internal i/o operation only, and
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is not available to the device driver.
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Each driver should declare in a MODULE_DEVICE_TABLE into which CU types/models
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and/or device types/models it is interested. This information can later be found
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in the struct ccw_device_id fields:
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struct ccw_device_id {
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__u16 match_flags;
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__u16 cu_type;
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__u16 dev_type;
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__u8 cu_model;
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__u8 dev_model;
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unsigned long driver_info;
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};
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The functions in ccw_driver should be used in the following way:
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probe: This function is called by the device layer for each device the driver
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is interested in. The driver should only allocate private structures
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to put in dev->driver_data and create attributes (if needed). Also,
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the interrupt handler (see below) should be set here.
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int (*probe) (struct ccw_device *cdev);
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Parameters: cdev - the device to be probed.
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remove: This function is called by the device layer upon removal of the driver,
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the device or the module. The driver should perform cleanups here.
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int (*remove) (struct ccw_device *cdev);
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Parameters: cdev - the device to be removed.
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set_online: This function is called by the common I/O layer when the device is
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activated via the 'online' attribute. The driver should finally
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setup and activate the device here.
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int (*set_online) (struct ccw_device *);
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Parameters: cdev - the device to be activated. The common layer has
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verified that the device is not already online.
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set_offline: This function is called by the common I/O layer when the device is
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de-activated via the 'online' attribute. The driver should shut
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down the device, but not de-allocate its private data.
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int (*set_offline) (struct ccw_device *);
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Parameters: cdev - the device to be deactivated. The common layer has
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verified that the device is online.
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notify: This function is called by the common I/O layer for some state changes
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of the device.
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Signalled to the driver are:
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* In online state, device detached (CIO_GONE) or last path gone
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(CIO_NO_PATH). The driver must return !0 to keep the device; for
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return code 0, the device will be deleted as usual (also when no
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notify function is registerd). If the driver wants to keep the
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device, it is moved into disconnected state.
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* In disconnected state, device operational again (CIO_OPER). The
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common I/O layer performs some sanity checks on device number and
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Device / CU to be reasonably sure if it is still the same device.
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If not, the old device is removed and a new one registered. By the
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return code of the notify function the device driver signals if it
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wants the device back: !0 for keeping, 0 to make the device being
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removed and re-registered.
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int (*notify) (struct ccw_device *, int);
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Parameters: cdev - the device whose state changed.
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event - the event that happened. This can be one of CIO_GONE,
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CIO_NO_PATH or CIO_OPER.
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The handler field of the struct ccw_device is meant to be set to the interrupt
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handler for the device. In order to accommodate drivers which use several
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distinct handlers (e.g. multi subchannel devices), this is a member of ccw_device
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instead of ccw_driver.
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The handler is registered with the common layer during set_online() processing
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before the driver is called, and is deregistered during set_offline() after the
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driver has been called. Also, after registering / before deregistering, path
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grouping resp. disbanding of the path group (if applicable) are performed.
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void (*handler) (struct ccw_device *dev, unsigned long intparm, struct irb *irb);
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Parameters: dev - the device the handler is called for
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intparm - the intparm which allows the device driver to identify
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the i/o the interrupt is associated with, or to recognize
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the interrupt as unsolicited.
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irb - interruption response block which contains the accumulated
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status.
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The device driver is called from the common ccw_device layer and can retrieve
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information about the interrupt from the irb parameter.
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1.3 ccwgroup devices
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--------------------
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The ccwgroup mechanism is designed to handle devices consisting of multiple ccw
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devices, like lcs or ctc.
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The ccw driver provides a 'group' attribute. Piping bus ids of ccw devices to
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this attributes creates a ccwgroup device consisting of these ccw devices (if
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possible). This ccwgroup device can be set online or offline just like a normal
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ccw device.
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Each ccwgroup device also provides an 'ungroup' attribute to destroy the device
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again (only when offline). This is a generic ccwgroup mechanism (the driver does
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not need to implement anything beyond normal removal routines).
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A ccw device which is a member of a ccwgroup device carries a pointer to the
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ccwgroup device in the driver_data of its device struct. This field must not be
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touched by the driver - it should use the ccwgroup device's driver_data for its
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private data.
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To implement a ccwgroup driver, please refer to include/asm/ccwgroup.h. Keep in
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mind that most drivers will need to implement both a ccwgroup and a ccw driver
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(unless you have a meta ccw driver, like cu3088 for lcs and ctc).
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2. Channel paths
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-----------------
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Channel paths show up, like subchannels, under the channel subsystem root (css0)
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and are called 'chp0.<chpid>'. They have no driver and do not belong to any bus.
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Please note, that unlike /proc/chpids in 2.4, the channel path objects reflect
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only the logical state and not the physical state, since we cannot track the
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latter consistently due to lacking machine support (we don't need to be aware
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of it anyway).
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status - Can be 'online' or 'offline'.
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Piping 'on' or 'off' sets the chpid logically online/offline.
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Piping 'on' to an online chpid triggers path reprobing for all devices
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the chpid connects to. This can be used to force the kernel to re-use
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a channel path the user knows to be online, but the machine hasn't
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created a machine check for.
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type - The physical type of the channel path.
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3. System devices
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-----------------
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3.1 xpram
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---------
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xpram shows up under devices/system/ as 'xpram'.
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3.2 cpus
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--------
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For each cpu, a directory is created under devices/system/cpu/. Each cpu has an
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attribute 'online' which can be 0 or 1.
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4. Other devices
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----------------
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4.1 Netiucv
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-----------
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The netiucv driver creates an attribute 'connection' under
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bus/iucv/drivers/netiucv. Piping to this attibute creates a new netiucv
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connection to the specified host.
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Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
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number is assigned sequentially to the connections defined via the 'connection'
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attribute.
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user - shows the connection partner.
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buffer - maximum buffer size.
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Pipe to it to change buffer size.
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