macOS: support zeroconf pmlogconf configurations

[tallpsmith]

Problem

The pcp-zeroconf package on Linux provides 18 extended pmlogger configurations for richer out-of-the-box metric recording — per-process stats, disk activity, filesystem metrics, etc. On macOS, this is explicitly gated out in src/pmlogconf/GNUmakefile:

ifeq "$(TARGET_OS)" "linux"
SUBDIRS += zeroconf
PMCHECK=zeroconf.pmcheck
else
PMCHECK=no.zeroconf.pmcheck
endif

The no.zeroconf.pmcheck simply reports "not currently available for Darwin."

Why there's no technical barrier

Investigation shows no technical reason for the Linux-only gate. The zeroconf pmlogconf configs use a probe mechanism that gracefully self-selects based on metric availability.

Configs that work on macOS (metrics exist in darwin/darwin_proc PMDAs)

Config	Probe	Status
atop-proc	proc.psinfo.rss values	Works (darwin_proc has this)
pidstat	proc.psinfo.rss values	Works (darwin_proc has this)
disk	force include	Works (darwin has disk.dev.*)
filesystem	force include	Works (darwin has filesys.*)
rpc	force include	Works (darwin has rpc.*)

Configs gracefully excluded on macOS (probe fails, no error)

Config	Probe	Why excluded
pidstat-summary	kernel.uname.sysname ~ Linux	Explicit Linux check
interrupts	kernel.percpu.interrupts.LOC	Linux-only metric
nfsclient	nfsclient.pages.read	Linux namespace
hugepages	mem.hugepages.totalsize > 0	Linux memory feature
hv-balloon	hyperv.balloon.state > 0	Hyper-V only
hv-balloon-summary	hyperv.balloon.state > 0	Hyper-V only
tapestat	tape.dev.in_flight	Linux tape devices
xfs-perdev	xfs.perdev.read	Linux filesystem
vmmemctl	mem.vmmemctl.target > 0	VMware balloon driver
numahugepages	mem.numa.hugepages.totalsize > 0	Linux NUMA
numastat	hinv.nnode > 1	macOS is single-node

Force-included but harmless (metrics absent, pmlogger handles gracefully)

Config	Notes
numa	NUMA metrics don't exist on macOS, no error
tty	tty.serial.* doesn't exist on macOS, no error

Nothing breaks. The probe mechanism was designed for exactly this kind of cross-platform graceful degradation.

Proposed Solution

Extend the TARGET_OS gate to explicitly include darwin:

ifeq "$(TARGET_OS)" "linux"
SUBDIRS += zeroconf
PMCHECK=zeroconf.pmcheck
else ifeq "$(TARGET_OS)" "darwin"
SUBDIRS += zeroconf
PMCHECK=zeroconf.pmcheck
else
PMCHECK=no.zeroconf.pmcheck
endif

This is conservative — explicit opt-in for Darwin only, avoiding accidental enablement on untested platforms (AIX, FreeBSD).

CI verification

Add to both .github/workflows/macOS.yml and .cirrus.yml after installation:

test -d /var/lib/pcp/config/pmlogconf/zeroconf && echo "zeroconf configs installed" || echo "zeroconf NOT installed"

Additional considerations

• The zeroconf.pmcheck script checks for $PCP_VAR_DIR/config/pmlogconf/zeroconf directory existence — works on macOS as-is.
• On Linux, pcp-zeroconf also sets PMLOGGER_INTERVAL=10 (vs default 60s). Should the macOS PKG do the same?
• The macOS postinstall doesn't currently start pmlogger or pmie via launchd. For zeroconf configs to have any effect, pmlogger needs to be running. This may need a parallel effort.