nix-builds: suspend/resume/observe the nix-build demon activity

nix-builds

#!/bin/sh

mapcflip () {
	local xs=$1; shift
	local x

	for x in $(echo $xs | sed 's/,/ /g')
	do
	        $(echo $@ | sed s/%/$x/)

 		local ex=$?
        	if test "${ex}" != 0
        	then exit ${ex}
        	fi
	done
}

lines2csv () {
	xargs echo | sed 's/ /,/g'
}

op_ls_root_pids() {
	for nixd_pid in $(pgrep nix-daemon)
	do
		echo "; builds of nix-daemon PID ${nixd_pid}"
		root_pids=`pgrep -P ${nixd_pid} | lines2csv`
		mapcflip "${root_pids}" ls -l /proc/%/cwd | grep -v 'root root' | cut -d' ' -f11- | cut -d- -f2-
	done
}

kill_stop() {
	kill -STOP $1
}
kill_cont() {
	kill -CONT $1
}

op_map() {
	local op="$1"; shift
	local pfx="$2"; shift
	for x in $*
	do
		${op} ${x} "${pfx}"
		op_map ${op} "${pfx}	" $(pgrep -P $x)
	done
}

op_tree() {
	local cut="$1"; shift
	local pfx="$1"; shift
	for x in $*
	do
		echo -n "${pfx}"
		ps -hp $x -o args | xargs echo | $cut
		op_tree "$cut" "${pfx}	" $(pgrep -P $x)
	done
}

case "$1" in
	tree )     op_tree "cut -c-160" "" $(pgrep -n nix-daemon);;
	treeful )  op_tree "cat"        "" $(pgrep -n nix-daemon);;
	suspend )  op_map kill_stop     "" $(pgrep -n nix-daemon);;
	resume )   op_map kill_cont     "" $(pgrep -n nix-daemon);;
	root | * ) op_ls_root_pids;;
esac