int pmLoadDerivedConfig(char *fname)
Each line of the file fname is either a comment line (with a ``#'' in the first position of the line) or the declaration of a derived performance metric, specified as:
White space is ignored in the lines.
For each line containing a derived metric definition, BR pmRegisterDerived (3) is called to register the new derived metric.
The result from pmLoadDerivedConfig will be the number of derived metrics loaded from fname else a value less than zero in the case of an error.
# sample derived metric definitions
bad_in_pkts = network.interface.in.errors + network.interface.in.drops
# note the following would need to be on a single line ...
disk.dev.read_pct = 100 * delta(disk.dev.read) /
(delta(disk.dev.read) + delta(disk.dev.write))