makemore

#!/bin/bash

set -eu -o pipefail

rdfd=${2:-3}
wrfd=${3:-$(($rdfd+1))}

if [[ -z $1 ]]; then
	echo >&2 "Usage: $0 <pid>"
	exit 1
fi

exe="$(realpath -eq /proc/$1/exe)"
if [[ -z "$exe" ]]; then
	echo >&2 "error: no such pid"
	exit 1
fi

exe_expect="$(realpath "$(which make)")"
if [[ "$exe" != "$exe_expect" ]]; then
	echo >&2 "error: pid $1 is $exe, not $exe_expect"
	exit 1
fi

rdpipe="$(readlink /proc/$1/fd/$rdfd)"
if [[ "$rdpipe" != pipe:* ]]; then
	echo >&2 "error: fd $rdfd is not a pipe; is this a parallel make?"
	exit 1
fi

wrpipe="$(readlink /proc/$1/fd/$wrfd)"
if [[ "$wrpipe" != pipe:* ]]; then
	echo >&2 "error: fd $wrfd is not a pipe; is this a parallel make?"
	exit 1
fi

if [[ "$rdpipe" != "$wrpipe" ]]; then
	echo >&2 "error: fd $rdfd and fd $wrfd are not the same pipe; is this a parallel make?"
	exit 1
fi

if ! echo -n '+' > /proc/$1/fd/$wrfd; then
	exit 1
fi

# TODO: show actual process name
echo >&2 "Successfully injected a jobserver token into make $1"