'\"macro stdmacro
.\"
.\" Copyright (c) 2009 Ken McDonell.  All Rights Reserved.
.\" 
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.\"
.TH PMLOADDERIVEDCONFIG 3 "" "Performance Co-Pilot"
.SH NAME
\f3pmLoadDerivedConfig\f1 \- load derived metric definitions from files
.SH "C SYNOPSIS"
.ft 3
#include <pcp/pmapi.h>
.sp
int pmLoadDerivedConfig(char *\fIpath\fP);
.sp
cc ... \-lpcp
.ft 1
.SH DESCRIPTION
.PP
Derived metrics may be used to extend the available metrics with
new (derived) metrics using simple arithmetic expressions.
The definitions of these metrics can be persisted and loaded
programatically by monitor tools using
.BR pmLoadDerivedConfig .
.PP
The
.I path
parameter defines a colon separated list of files and/or
directories (the syntax is the same as for the
.B $PATH
variable for
.BR sh (1)),
from which derived metric specifications are to be sourced.
The
.I path
components are expanded into a list of files as follows: if a component
is a file, then that file is added to the list, else if a component
is a directory then recursive descent is used to enumerate all
files below that directory and these are added to the list.
Each file in the resulting list is parsed in order, and according to
the derived metrics syntax described below.
.PP
Each line of the file(s) identified by
.I path
is either a comment line (with a ``#'' in the first position of the line)
or the declaration of a derived performance metric, specified as:
.IP * 2n
the name of the derived metric, using the same ``dot notation'' syntax
that is used for PCP performance metrics, see
.BR PCPIntro (1)
and
.BR pmns (5).
.IP * 2n
an equals sign (``='')
.IP * 2n
a valid expression for a derived metric, as described in
.BR pmRegisterDerived (3).
.PP
White space is ignored in the lines.
.PP
For each line containing a derived metric definition,
.BR pmRegisterDerived (3)
is called to register the new derived metric.
.PP
Because
.B pmLoadDerivedConfig
may process many files, each of which may contain many derived metric
specifications, it is not possible to provide very specific error
status on return.
Hence the result from
.B pmLoadDerivedConfig
will be the number of derived metrics successfully loaded from
files on the given
.IR path .
Catastrophic errors such as not being able to open one of the
files on the given
.I path
will cause an immediate return with a negative return value
that can be passed to
.BR pmErrStr (3)
to obtain the associated error message.
.PP
When errors are encountered in the derived metric specifications
diagnostic messages are generated by
.BR pmRegisterDerived (3)
and displayed via
.BR pmprintf (3).
.SH EXAMPLE
.nf
# 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))
.fi
.SH SEE ALSO
.BR sh (1),
.BR PCPIntro (1),
.BR PMAPI (3),
.BR pmRegisterDerived (3),
.BR pmprintf (3)
and
.BR pmns (5).