The rsyslog “call” statement

The rsyslog “call” statement is used to tie rulesets together. It is modelled after the usual programming language “call” statement. Think of a ruleset as a subroutine (what it really is!) and you get the picture.

The “call” statement can be used to call into any type of rulesets. If a rule set has a queue assigned, the message will be posted to that queue and processed asynchronously. Otherwise, the ruleset will be executed synchronously and control returns to right after the call when the rule set has finished execution.

Note that there is an important difference between asynchronous and synchronous execution in regard to the “stop” statement. It will not affect processing of the original message when run asynchronously.

The “call” statement replaces the deprecated omruleset module. It offers all capabilities omruleset has, but works in a much more efficient way. Note that omruleset was a hack that made calling rulesets possible within the constraints of the pre-v7 engine. “call” is the clean solution for the new engine. Especially for rulesets without associated queues (synchronous operation), it has zero overhead (really!). omruleset always needs to duplicate messages, which usually means at least ~250 bytes of memory writes, some allocs and frees - and even more performance-intense operations.