3 Author: Gerald Schaefer (geraldsc@de.ibm.com)
6 Linux API for read access to z/VM Monitor Records
7 =================================================
12 This item delivers a new Linux API in the form of a misc char device that is
13 useable from user space and allows read access to the z/VM Monitor Records
14 collected by the *MONITOR System Service of z/VM.
19 The z/VM guest on which you want to access this API needs to be configured in
20 order to allow IUCV connections to the *MONITOR service, i.e. it needs the
21 IUCV *MONITOR statement in its user entry. If the monitor DCSS to be used is
22 restricted (likely), you also need the NAMESAVE <DCSS NAME> statement.
23 This item will use the IUCV device driver to access the z/VM services, so you
24 need a kernel with IUCV support. You also need z/VM version 4.4 or 5.1.
26 There are two options for being able to load the monitor DCSS (examples assume
27 that the monitor DCSS begins at 144 MB and ends at 152 MB). You can query the
28 location of the monitor DCSS with the Class E privileged CP command Q NSS MAP
29 (the values BEGPAG and ENDPAG are given in units of 4K pages).
31 See also "CP Command and Utility Reference" (SC24-6081-00) for more information
32 on the DEF STOR and Q NSS MAP commands, as well as "Saved Segments Planning
33 and Administration" (SC24-6116-00) for more information on DCSSes.
37 You can use the CP command DEF STOR CONFIG to define a "memory hole" in your
38 guest virtual storage around the address range of the DCSS.
40 Example: DEF STOR CONFIG 0.140M 200M.200M
42 This defines two blocks of storage, the first is 140MB in size an begins at
43 address 0MB, the second is 200MB in size and begins at address 200MB,
44 resulting in a total storage of 340MB. Note that the first block should
45 always start at 0 and be at least 64MB in size.
49 Your guest virtual storage has to end below the starting address of the DCSS
50 and you have to specify the "mem=" kernel parameter in your parmfile with a
51 value greater than the ending address of the DCSS.
53 Example: DEF STOR 140M
55 This defines 140MB storage size for your guest, the parameter "mem=160M" is
56 added to the parmfile.
61 The char device is implemented as a kernel module named "monreader",
62 which can be loaded via the modprobe command, or it can be compiled into the
63 kernel instead. There is one optional module (or kernel) parameter, "mondcss",
64 to specify the name of the monitor DCSS. If the module is compiled into the
65 kernel, the kernel parameter "monreader.mondcss=<DCSS NAME>" can be specified
68 The default name for the DCSS is "MONDCSS" if none is specified. In case that
69 there are other users already connected to the *MONITOR service (e.g.
70 Performance Toolkit), the monitor DCSS is already defined and you have to use
71 the same DCSS. The CP command Q MONITOR (Class E privileged) shows the name
72 of the monitor DCSS, if already defined, and the users connected to the
74 Refer to the "z/VM Performance" book (SC24-6109-00) on how to create a monitor
75 DCSS if your z/VM doesn't have one already, you need Class E privileges to
76 define and save a DCSS.
80 modprobe monreader mondcss=MYDCSS
82 This loads the module and sets the DCSS name to "MYDCSS".
86 This API provides no interface to control the *MONITOR service, e.g. specify
87 which data should be collected. This can be done by the CP command MONITOR
88 (Class E privileged), see "CP Command and Utility Reference".
90 Device nodes with udev:
91 -----------------------
92 After loading the module, a char device will be created along with the device
93 node /<udev directory>/monreader.
95 Device nodes without udev:
96 --------------------------
97 If your distribution does not support udev, a device node will not be created
98 automatically and you have to create it manually after loading the module.
99 Therefore you need to know the major and minor numbers of the device. These
100 numbers can be found in /sys/class/misc/monreader/dev.
101 Typing cat /sys/class/misc/monreader/dev will give an output of the form
102 <major>:<minor>. The device node can be created via the mknod command, enter
103 mknod <name> c <major> <minor>, where <name> is the name of the device node
109 # cat /sys/class/misc/monreader/dev
111 # mknod /dev/monreader c 10 63
113 This loads the module with the default monitor DCSS (MONDCSS) and creates a
118 The following file operations are supported: open, release, read, poll.
119 There are two alternative methods for reading: either non-blocking read in
120 conjunction with polling, or blocking read without polling. IOCTLs are not
125 Reading from the device provides a 12 Byte monitor control element (MCE),
126 followed by a set of one or more contiguous monitor records (similar to the
127 output of the CMS utility MONWRITE without the 4K control blocks). The MCE
128 contains information on the type of the following record set (sample/event
129 data), the monitor domains contained within it and the start and end address
130 of the record set in the monitor DCSS. The start and end address can be used
131 to determine the size of the record set, the end address is the address of the
132 last byte of data. The start address is needed to handle "end-of-frame" records
133 correctly (domain 1, record 13), i.e. it can be used to determine the record
134 start offset relative to a 4K page (frame) boundary.
136 See "Appendix A: *MONITOR" in the "z/VM Performance" document for a description
137 of the monitor control element layout. The layout of the monitor records can
138 be found here (z/VM 5.1): http://www.vm.ibm.com/pubs/mon510/index.html
140 The layout of the data stream provided by the monreader device is as follows:
144 <first set of records> |
147 <last set of records> /
151 There may be more than one combination of MCE and corresponding record set
152 within one data set and the end of each data set is indicated by a successful
153 read with a return value of 0 (0 byte read).
154 Any received data must be considered invalid until a complete set was
155 read successfully, including the closing 0 byte read. Therefore you should
156 always read the complete set into a buffer before processing the data.
158 The maximum size of a data set can be as large as the size of the
159 monitor DCSS, so design the buffer adequately or use dynamic memory allocation.
160 The size of the monitor DCSS will be printed into syslog after loading the
161 module. You can also use the (Class E privileged) CP command Q NSS MAP to
162 list all available segments and information about them.
164 As with most char devices, error conditions are indicated by returning a
165 negative value for the number of bytes read. In this case, the errno variable
166 indicates the error condition:
168 EIO: reply failed, read data is invalid and the application
169 should discard the data read since the last successful read with 0 size.
170 EFAULT: copy_to_user failed, read data is invalid and the application should
171 discard the data read since the last successful read with 0 size.
172 EAGAIN: occurs on a non-blocking read if there is no data available at the
173 moment. There is no data missing or corrupted, just try again or rather
174 use polling for non-blocking reads.
175 EOVERFLOW: message limit reached, the data read since the last successful
176 read with 0 size is valid but subsequent records may be missing.
178 In the last case (EOVERFLOW) there may be missing data, in the first two cases
179 (EIO, EFAULT) there will be missing data. It's up to the application if it will
180 continue reading subsequent data or rather exit.
184 Only one user is allowed to open the char device. If it is already in use, the
185 open function will fail (return a negative value) and set errno to EBUSY.
186 The open function may also fail if an IUCV connection to the *MONITOR service
187 cannot be established. In this case errno will be set to EIO and an error
188 message with an IPUSER SEVER code will be printed into syslog. The IPUSER SEVER
189 codes are described in the "z/VM Performance" book, Appendix A.
193 As soon as the device is opened, incoming messages will be accepted and they
194 will account for the message limit, i.e. opening the device without reading
195 from it will provoke the "message limit reached" error (EOVERFLOW error code)
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