The MSGID parameter was introduced with z/OS 1.2 to allow SLIP traps
to be set based on message identifier. For the purpose of this xample,
the message identifier is IEFnnnI where nnn is 3 digits:
This causes the message to be trapped synchronously and an SVC dump to
be scheduled if a message is issued either via SVC or branch-entry to WTO with message identifier IEFnnnI appearing at the beginning of
the message text.
At the time that the SLIP matches, R3 points to the message text,
which can be used to perform additional filtering, e.g.
would look at offset 18 (12 hex) in the message text for the
hexadecimal value C3C1E3.
Some exceptions are identified in the System Commands publication
where the environment prevents the SLIP trap from being taken. In
these situations, another approach must be used.
This approach was described in the IBM-Main newsgroup in 2001 (See
Big Iron Newsgroups.) An MPF exit is established for the specific MSGID in an MPFLSTxx member:
and set MPF=xx is used to establish this MPF exit (provided by IBM).
The exit issues an S06F abend if this message is seen by MPF.
Before or soon after the MPF exit is enabled, a SLIP trap is established:
to trap for this abend. At the time of the abend, R2 will point to the
message text. See notes above for an example; note that R2 is used
instead of R3.
This trap may be taken some time later, so the MSGID SLIP trap is
preferred where it can be used.