mezoura: Add new package

`mezoura` uses `tc` subsystem eBPF hook (direct-action [0]).
It's attached as a TC classifier for both ingress and egress.
The eBPF program is used to measure traffic (bandwidth and packets per
second) from/to the internet (non-private addresses).

It utilizes `uci` to parse static entries for DHCP (/etc/config/dhcp)
to map MAC addresses -> hostnames.

For each new IP/MAC address pair seen on the network, it attempts to resolve the
MAC address to a hostname. If there's no mapping, the entry is skipped.

It works for both v4 and v6 without having to maintain some weird
iptables rules to count packets/bytes as seen in other packages.

Lastly, it exposes a prometheus exporter for a widely used method to
consume the metrics held in the eBPF maps.

There's an option to disable exposing the embedded prometheus exporter.
The exporter component, flushes the metrics to `/tmp/prom_c`.
From that point, `prometheus-node-exporter-lua-textfile` can be used to
consume the metrics instead of exposing yet another service.

[0]: https://man7.org/linux/man-pages/man8/tc-bpf.8.html

Signed-off-by: Linos Giannopoulos <linosgian00@gmail.com>

utils/mezoura/Makefile

@@ -0,0 +1,50 @@
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=mezoura
+PKG_RELEASE:=1
+
+PKG_SOURCE_PROTO:=git
+PKG_SOURCE_URL:=https://github.com/linosgian/mezoura
+PKG_SOURCE_DATE:=2022-02-01
+PKG_SOURCE_VERSION:=ae8969d207f9f68535cc9f5cabdf8345226352e2
+PKG_MIRROR_HASH:=3cd82bf5cf5754aaffbb7656fc3e0c525ac925f42a70eb23aa3004d1e2542096
+
+PKG_MAINTAINER:=Linos Giannopoulos <linosgian00@gmail.com>
+PKG_LICENSE:=GPL-3.0-or-later
+
+PKG_BUILD_DEPENDS:=bpf-headers
+PKG_FLAGS:=nonshared
+
+include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/cmake.mk
+include $(INCLUDE_DIR)/bpf.mk
+
+define Package/mezoura
+  SECTION:=utils
+  CATEGORY:=Base system
+  TITLE:=eBPF-based bandwidth monitoring utility
+  DEPENDS:=+libbpf +kmod-sched-bpf +tc-full +libuci $(BPF_DEPENDS)
+endef
+
+define Build/Compile
+	$(call CompileBPF,$(PKG_BUILD_DIR)/mezoura.bpf.c)
+	$(Build/Compile/Default)
+endef
+
+define Package/mezoura/conffiles
+/etc/config/mezoura
+endef
+
+define Package/mezoura/install
+	$(INSTALL_DIR) $(1)/etc/config
+	$(INSTALL_CONF) ./files/etc/config/mezoura $(1)/etc/config/mezoura
+	$(INSTALL_DIR) $(1)/etc/init.d
+	$(INSTALL_BIN) ./files/etc/init.d/mezoura $(1)/etc/init.d/mezoura
+	$(INSTALL_DIR) $(1)/lib/bpf
+	$(INSTALL_DATA) $(PKG_BUILD_DIR)/mezoura.bpf.o $(1)/lib/bpf
+	$(INSTALL_DIR) $(1)/usr/bin
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/mezoura $(1)/usr/bin
+endef
+
+$(eval $(call BuildPackage,mezoura))

utils/mezoura/files/etc/config/mezoura

@@ -0,0 +1,4 @@
+config mezoura 'main'
+	option exporter_port '9999'
+	option exporter '1'
+	list interface 'lan'

utils/mezoura/files/etc/init.d/mezoura

@@ -0,0 +1,53 @@
+#!/bin/sh /etc/rc.common
+
+START=60
+
+USE_PROCD=1
+PROG=/usr/bin/mezoura
+
+. /lib/functions/network.sh
+
+add_iface_v4() {
+	local addr
+	network_get_subnet addr "$1"
+	network_get_physdev iface "$1"
+	addr=$(echo "$addr" | sed "s/ /\//")
+	procd_append_param command -4 "${addr}/${iface}"
+}
+
+start_service() {
+	local iface interface6 port addr6
+
+	config_load "mezoura"
+	config_get interface6 main interface6 ""
+	config_get_bool exporter main exporter '1'
+	config_get port main listen_port "9999"
+	config_get config_file main config_file ""
+
+	procd_open_instance
+	procd_set_param command "$PROG"
+	[ $exporter -eq 1 ] && procd_append_param command -e
+	if [ -n "$interface6" ]; then
+		network_get_prefix6 addr6 "$interface6"
+
+		addr6=$(echo "$addr6" | sed "s/ /\//")
+		procd_append_param command -6 "${addr6}"
+	fi
+	procd_append_param command -p "${port}"
+	config_list_foreach 'main' interface  "add_iface_v4"
+
+	procd_set_param respawn
+	procd_close_instance
+}
+
+stop_service() {
+	local pid
+
+	# kill all previous mezoura processes
+	for pid in $(pidof mezoura)
+	do
+		[ "$pid" = "$$" ] && continue
+		[ -e "/proc/$pid/stat" ] && kill $pid
+	done
+	return 0;
+}