Here is the IBM KB article information:
Determining the Offsets for Pool Information Using the Retrieve System
Status (QWCRSSTS) API
Incident Summary
Problem Summary:
Format SSTS0400 of t he Retrieve System Status (QWCRSSTS) API is called
from a CL program to retrieve the pool information from the system. The
incorrect value is returned for the Tuning Maximum Pool Size %
parameter. The WRKSHRPOOL command screen showed the correct pool
information.
Resolution:
The user was using the incorrect offset for the Pool Information in the
CL program. The program was using offset 151 and 155, but the correct
data was at offset 157 and 161. The offset is determined as follows:
The offset to Pool Information is returned by the API. For R520, the
offset for the Pool Information is 56 ; however, if more information is
added to the header, it could change in a future release. You could use
the offset returned by the API in the program to protect against a
future change in offset. For example, using the attached program rather
than hard coding 101 for the pool name allows use of the returned pool
information offset, plus 45 for the position of the pool name in the
pool information:
dcl &offsetpool *dec 8 0 /* decimal offset to pool information */
dcl &offset *dec 8 0 /* offset to information in pool information */
chgvar &offsetpinf (%sst(&rcvvar 49 4)) /* get pool information offset
from receiver */
chgvar &offsetpool (%bin(&offsetpinf)) /* convert to pool information
offset to decimal */
chgvar &offset (&offsetpool + 45) /* add to get offset to pool name in
receiver */
chgvar &poolnam (%sst(&rcvvar &offset 10)) /* get pool name from
receiver */
The SSTS0400 format structure below is documentation taken from the
QWCRSSTS API using the InfoCenter Web site. It returns a header portion
that has the offsets documented. Following the header is information for
each pool. The offset to that information is returned in the header in
field:
48
30
BINARY(4)
Offset to pool information
This is the field that contains the 56 (offset to first pool returned)
mentioned above. Because the program requests only one pool to be
returned, the user has taken the shortcut of determining the offsets to
a couple of the fields in the pool information. The pool information
does not have the offsets documented for you. However, if we filled in
relative offsets (from the start of pool information rather than the
entire receiver), they would be:
0
BINARY(4)
System pool
4
BINARY(4)
Pool size
8
BINARY(4)
Reserved size
12
BINARY(4)
Maximum active threads
16
BINARY(4)
Database faults
20
BINARY(4)
Database pages
24
BINARY(4)
Nondatabase faults
28
BINARY(4)
Nondatabase pages
32
BINARY(4)
Active to wait
36
BINARY(4)
Wait to ineligible
40
BINARY(4)
Active to ineligible
44
CHAR(10)
Pool name
54
CHAR(10)
Subsystem name
64
CHAR(10)
Subsystem library name
74
CHAR(10)
Paging option
84
BINARY(4)
Defined size
88
BINARY(4)
Current threads
92
BINARY(4)
Current ineligible threads
96
BINARY(4)
Tuning priority
100
BINARY(4)
Tuning minimum pool size %
104
BINARY(4)
Tuning maximum pool size %
BINARY(4)
Tuning minimum faults
BINARY(4)
Tuning per-thread faults
BINARY(4)
Tuning maximum faults
CHAR(50)
Description
CHAR(1)
Status
CHAR(*)
To get the offset to the Tuning minimum pool size % from the beginning
of the receiver, get the offset to the pool information (56 ) and add
the offset of the minimum percent within the pool information 100 . You
add 1 to go from an offset to a position in CL sub-stringing:
157 = 56 + 100 + 1
The concern about not hardcoding the offset is in the InfoCenter in the
OS/400 API concepts section:
Offset Values and Lengths
When using an API that generates a list into a user space, the offset
values and lengths returned by the API in the generic user space header
must be used to step through the list rather than specifying what the
current version of the API returns. This is the result of:
o
The offset values to the different sections of the user space may change
in future releases.
o
The length of the entries in the list data section of the user space may
change in future releases.
As long as the HLL application program uses the offset values and
lengths returned in the generic header of the user space, your program
will run in future releases of the OS/400 licensed program.
References:
None.
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