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, 13 insertions, 4 deletions

diff --git a/Header.c b/Header.c
index d2d7f694..0fdafea5 100644
--- a/Header.c
+++ b/Header.c
@@ -13,6 +13,8 @@ in the source distribution for its full text.
 #include <string.h>
 
 #include "CRT.h"
+#include "CPUMeter.h"
+#include "DynamicMeter.h"
 #include "Macros.h"
 #include "Object.h"
 #include "Platform.h"
@@ -70,7 +72,10 @@ void Header_writeBackToSettings(const Header* this) {
       for (int i = 0; i < len; i++) {
          const Meter* meter = (Meter*) Vector_get(vec, i);
          char* name;
-         if (meter->param) {
+         if (meter->param && As_Meter(meter) == &DynamicMeter_class) {
+            const char* dynamic = DynamicMeter_lookup(this->pl, meter->param);
+            xAsprintf(&name, "%s(%s)", As_Meter(meter)->name, dynamic);
+         } else if (meter->param && As_Meter(meter) == &CPUMeter_class) {
             xAsprintf(&name, "%s(%u)", As_Meter(meter)->name, meter->param);
          } else {
             xAsprintf(&name, "%s", As_Meter(meter)->name);
@@ -87,9 +92,13 @@ MeterModeId Header_addMeterByName(Header* this, const char* name, int column) {
    char* paren = strchr(name, '(');
    unsigned int param = 0;
    if (paren) {
-      int ok = sscanf(paren, "(%10u)", &param);
-      if (!ok)
-         param = 0;
+      char* end, dynamic[32] = {0};
+      int ok = sscanf(paren, "(%10u)", &param); // CPUMeter
+      if (!ok) {
+         ok = sscanf(paren, "(%30s)", dynamic); // DynamicMeter
+         if (ok && (end = strrchr(dynamic, ')'))) *end = '\0';
+         param = ok ? DynamicMeter_search(this->pl, dynamic) : 0;
+      }
       *paren = '\0';
    }
    MeterModeId mode = TEXT_METERMODE;