Functions are conveniently packaged reusable software: it would be a shame to have to duplicate a complex condition expression or logging directive in every placed it's used. So, systemtap lets you define functions of your own. Like global variables, systemtap functions may be defined anywhere in the script. They may take any number of string or numeric arguments (by value), and may return a single string or number. The parameter types are inferred as for ordinary variables, and must be consistent throughout the program. Local and global script variables are available, but target variables are not. That's because there is no specific debugging-level context associated with a function.
A function is defined with the keyword function followed by a
name. Then comes a comma-separated formal argument list (just a list
of variable names). The { }-enclosed body consists of any list
of statements, including expressions that call functions. Recursion
is possible, up to a nesting depth limit. Figure 6
displays function syntax.
