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, 5 insertions, 1 deletions

diff --git a/Meter.h b/Meter.h
index cd9c9b8e..40cad332 100644
--- a/Meter.h
+++ b/Meter.h
@@ -53,14 +53,16 @@ typedef void(*Meter_Done)(Meter*);
 typedef void(*Meter_UpdateMode)(Meter*, int);
 typedef void(*Meter_UpdateValues)(Meter*);
 typedef void(*Meter_Draw)(Meter*, int, int, int);
+typedef void(*Meter_GetUiName)(const Meter*, char*, size_t);
 
 typedef struct MeterClass_ {
    const ObjectClass super;
    const Meter_Init init;
    const Meter_Done done;
    const Meter_UpdateMode updateMode;
-   const Meter_Draw draw;
    const Meter_UpdateValues updateValues;
+   const Meter_Draw draw;
+   const Meter_GetUiName getUiName;
    const int defaultMode;
    const double total;
    const int* const attributes;
@@ -80,6 +82,8 @@ typedef struct MeterClass_ {
 #define Meter_drawFn(this_)            As_Meter(this_)->draw
 #define Meter_doneFn(this_)            As_Meter(this_)->done
 #define Meter_updateValues(this_)      As_Meter(this_)->updateValues((Meter*)(this_))
+#define Meter_getUiNameFn(this_)       As_Meter(this_)->getUiName
+#define Meter_getUiName(this_,n_,l_)   As_Meter(this_)->getUiName((const Meter*)(this_),n_,l_)
 #define Meter_defaultMode(this_)       As_Meter(this_)->defaultMode
 #define Meter_attributes(this_)        As_Meter(this_)->attributes
 #define Meter_name(this_)              As_Meter(this_)->name