Add a new DynamicMeter class for runtime Meter extension

This commit is based on exploratory work by Sohaib Mohamed.
The end goal is two-fold - to support addition of Meters we
build via configuration files for both the PCP platform and
for scripts ( https://github.com/htop-dev/htop/issues/526 )

Here, we focus on generic code and the PCP support.  A new
class DynamicMeter is introduced - it uses the special case
'param' field handling that previously was used only by the
CPUMeter, such that every runtime-configured Meter is given
a unique identifier.  Unlike with the CPUMeter this is used
internally only.  When reading/writing to htoprc instead of
CPU(N) - where N is an integer param (CPU number) - we use
the string name for each meter.  For example, if we have a
configuration for a DynamicMeter for some Redis metrics, we
might read and write "Dynamic(redis)".  This identifier is
subsequently matched (back) up to the configuration file so
we're able to re-create arbitrary user configurations.

The PCP platform configuration file format is fairly simple.
We expand configs from several directories, including the
users homedir alongside htoprc (below htop/meters/) and also
/etc/pcp/htop/meters.  The format will be described via a
new pcp-htop(5) man page, but its basically ini-style and
each Meter has one or more metric expressions associated, as
well as specifications for labels, color and so on via a dot
separated notation for individual metrics within the Meter.

A few initial sample configuration files are provided below
./pcp/meters that give the general idea.  The PCP "derived"
metric specification - see pmRegisterDerived(3) - is used
as the syntax for specifying metrics in PCP DynamicMeters.

1 files changed, 14 insertions, 1 deletions

diff --git a/pcp/Platform.h b/pcp/Platform.h
index cd90bc00..7cf3722b 100644
--- a/pcp/Platform.h
+++ b/pcp/Platform.h
@@ -24,6 +24,7 @@ in the source distribution for its full text.
 #include "Action.h"
 #include "BatteryMeter.h"
 #include "DiskIOMeter.h"
+#include "Hashtable.h"
 #include "Meter.h"
 #include "NetworkIOMeter.h"
 #include "Process.h"
@@ -247,14 +248,26 @@ bool Metric_iterate(Metric metric, int* instp, int* offsetp);
 
 pmAtomValue* Metric_values(Metric metric, pmAtomValue *atom, int count, int type);
 
+const pmDesc* Metric_desc(Metric metric);
+
 int Metric_instanceCount(Metric metric);
 
 int Metric_instanceOffset(Metric metric, int inst);
 
-pmAtomValue *Metric_instance(Metric metric, int inst, int offset, pmAtomValue *atom, int type);
+pmAtomValue* Metric_instance(Metric metric, int inst, int offset, pmAtomValue *atom, int type);
+
+int Platform_addMetric(Metric id, const char *name);
 
 void Platform_gettime_realtime(struct timeval* tv, uint64_t* msec);
 
 void Platform_gettime_monotonic(uint64_t* msec);
 
+Hashtable* Platform_dynamicMeters(void);
+
+void Platform_dynamicMeterInit(Meter* meter);
+
+void Platform_dynamicMeterUpdateValues(Meter* meter);
+
+void Platform_dynamicMeterDisplay(const Meter* meter, RichString* out);
+
 #endif