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-
-Date : 2004-Nov-26
-Author: Gerald Schaefer (geraldsc@de.ibm.com)
-
-
- Linux API for read access to z/VM Monitor Records
- =================================================
-
-
-Description
-===========
-This item delivers a new Linux API in the form of a misc char device that is
-useable from user space and allows read access to the z/VM Monitor Records
-collected by the *MONITOR System Service of z/VM.
-
-
-User Requirements
-=================
-The z/VM guest on which you want to access this API needs to be configured in
-order to allow IUCV connections to the *MONITOR service, i.e. it needs the
-IUCV *MONITOR statement in its user entry. If the monitor DCSS to be used is
-restricted (likely), you also need the NAMESAVE <DCSS NAME> statement.
-This item will use the IUCV device driver to access the z/VM services, so you
-need a kernel with IUCV support. You also need z/VM version 4.4 or 5.1.
-
-There are two options for being able to load the monitor DCSS (examples assume
-that the monitor DCSS begins at 144 MB and ends at 152 MB). You can query the
-location of the monitor DCSS with the Class E privileged CP command Q NSS MAP
-(the values BEGPAG and ENDPAG are given in units of 4K pages).
-
-See also "CP Command and Utility Reference" (SC24-6081-00) for more information
-on the DEF STOR and Q NSS MAP commands, as well as "Saved Segments Planning
-and Administration" (SC24-6116-00) for more information on DCSSes.
-
-1st option:
------------
-You can use the CP command DEF STOR CONFIG to define a "memory hole" in your
-guest virtual storage around the address range of the DCSS.
-
-Example: DEF STOR CONFIG 0.140M 200M.200M
-
-This defines two blocks of storage, the first is 140MB in size an begins at
-address 0MB, the second is 200MB in size and begins at address 200MB,
-resulting in a total storage of 340MB. Note that the first block should
-always start at 0 and be at least 64MB in size.
-
-2nd option:
------------
-Your guest virtual storage has to end below the starting address of the DCSS
-and you have to specify the "mem=" kernel parameter in your parmfile with a
-value greater than the ending address of the DCSS.
-
-Example: DEF STOR 140M
-
-This defines 140MB storage size for your guest, the parameter "mem=160M" is
-added to the parmfile.
-
-
-User Interface
-==============
-The char device is implemented as a kernel module named "monreader",
-which can be loaded via the modprobe command, or it can be compiled into the
-kernel instead. There is one optional module (or kernel) parameter, "mondcss",
-to specify the name of the monitor DCSS. If the module is compiled into the
-kernel, the kernel parameter "monreader.mondcss=<DCSS NAME>" can be specified
-in the parmfile.
-
-The default name for the DCSS is "MONDCSS" if none is specified. In case that
-there are other users already connected to the *MONITOR service (e.g.
-Performance Toolkit), the monitor DCSS is already defined and you have to use
-the same DCSS. The CP command Q MONITOR (Class E privileged) shows the name
-of the monitor DCSS, if already defined, and the users connected to the
-*MONITOR service.
-Refer to the "z/VM Performance" book (SC24-6109-00) on how to create a monitor
-DCSS if your z/VM doesn't have one already, you need Class E privileges to
-define and save a DCSS.
-
-Example:
---------
-modprobe monreader mondcss=MYDCSS
-
-This loads the module and sets the DCSS name to "MYDCSS".
-
-NOTE:
------
-This API provides no interface to control the *MONITOR service, e.g. specify
-which data should be collected. This can be done by the CP command MONITOR
-(Class E privileged), see "CP Command and Utility Reference".
-
-Device nodes with udev:
------------------------
-After loading the module, a char device will be created along with the device
-node /<udev directory>/monreader.
-
-Device nodes without udev:
---------------------------
-If your distribution does not support udev, a device node will not be created
-automatically and you have to create it manually after loading the module.
-Therefore you need to know the major and minor numbers of the device. These
-numbers can be found in /sys/class/misc/monreader/dev.
-Typing cat /sys/class/misc/monreader/dev will give an output of the form
-<major>:<minor>. The device node can be created via the mknod command, enter
-mknod <name> c <major> <minor>, where <name> is the name of the device node
-to be created.
-
-Example:
---------
-# modprobe monreader
-# cat /sys/class/misc/monreader/dev
-10:63
-# mknod /dev/monreader c 10 63
-
-This loads the module with the default monitor DCSS (MONDCSS) and creates a
-device node.
-
-File operations:
-----------------
-The following file operations are supported: open, release, read, poll.
-There are two alternative methods for reading: either non-blocking read in
-conjunction with polling, or blocking read without polling. IOCTLs are not
-supported.
-
-Read:
------
-Reading from the device provides a 12 Byte monitor control element (MCE),
-followed by a set of one or more contiguous monitor records (similar to the
-output of the CMS utility MONWRITE without the 4K control blocks). The MCE
-contains information on the type of the following record set (sample/event
-data), the monitor domains contained within it and the start and end address
-of the record set in the monitor DCSS. The start and end address can be used
-to determine the size of the record set, the end address is the address of the
-last byte of data. The start address is needed to handle "end-of-frame" records
-correctly (domain 1, record 13), i.e. it can be used to determine the record
-start offset relative to a 4K page (frame) boundary.
-
-See "Appendix A: *MONITOR" in the "z/VM Performance" document for a description
-of the monitor control element layout. The layout of the monitor records can
-be found here (z/VM 5.1): http://www.vm.ibm.com/pubs/mon510/index.html
-
-The layout of the data stream provided by the monreader device is as follows:
-...
-<0 byte read>
-<first MCE> \
-<first set of records> |
-... |- data set
-<last MCE> |
-<last set of records> /
-<0 byte read>
-...
-
-There may be more than one combination of MCE and corresponding record set
-within one data set and the end of each data set is indicated by a successful
-read with a return value of 0 (0 byte read).
-Any received data must be considered invalid until a complete set was
-read successfully, including the closing 0 byte read. Therefore you should
-always read the complete set into a buffer before processing the data.
-
-The maximum size of a data set can be as large as the size of the
-monitor DCSS, so design the buffer adequately or use dynamic memory allocation.
-The size of the monitor DCSS will be printed into syslog after loading the
-module. You can also use the (Class E privileged) CP command Q NSS MAP to
-list all available segments and information about them.
-
-As with most char devices, error conditions are indicated by returning a
-negative value for the number of bytes read. In this case, the errno variable
-indicates the error condition:
-
-EIO: reply failed, read data is invalid and the application
- should discard the data read since the last successful read with 0 size.
-EFAULT: copy_to_user failed, read data is invalid and the application should
- discard the data read since the last successful read with 0 size.
-EAGAIN: occurs on a non-blocking read if there is no data available at the
- moment. There is no data missing or corrupted, just try again or rather
- use polling for non-blocking reads.
-EOVERFLOW: message limit reached, the data read since the last successful
- read with 0 size is valid but subsequent records may be missing.
-
-In the last case (EOVERFLOW) there may be missing data, in the first two cases
-(EIO, EFAULT) there will be missing data. It's up to the application if it will
-continue reading subsequent data or rather exit.
-
-Open:
------
-Only one user is allowed to open the char device. If it is already in use, the
-open function will fail (return a negative value) and set errno to EBUSY.
-The open function may also fail if an IUCV connection to the *MONITOR service
-cannot be established. In this case errno will be set to EIO and an error
-message with an IPUSER SEVER code will be printed into syslog. The IPUSER SEVER
-codes are described in the "z/VM Performance" book, Appendix A.
-
-NOTE:
------
-As soon as the device is opened, incoming messages will be accepted and they
-will account for the message limit, i.e. opening the device without reading
-from it will provoke the "message limit reached" error (EOVERFLOW error code)
-eventually.
-