[dhcp-relay]: Add DHCP Relay Monitor (#3886)

DHCP relay MONitor (dhcpmon) keeps track of DORA messages. If DHCP Relay
is detected to be not forwarding DORA message, dhcpmon will log such event
to syslog. Under the hood dhcpmon keeps counts of clients DR messages,
forwarded DR messages, DHCP server OA messages, and forwarded OA messages.
dhcpmon will check every 12 sec (configurable) if counts are monotonically
increasing and record snapshot of those counters. dhcpmon will report
discrepancies when detected between current counters and snapshot counters.

pull-request: sonic-net/sonic-buildimage#3886
signed-off-by: Tamer Ahmed <[email protected]>

Makefile

@@ -0,0 +1,44 @@
+RM := rm -rf
+DHCPMON_TARGET := dhcpmon
+CP := cp
+MKDIR := mkdir
+CC := gcc
+MV := mv
+
+# All of the sources participating in the build are defined here
+-include src/subdir.mk
+-include objects.mk
+
+ifneq ($(MAKECMDGOALS),clean)
+ifneq ($(strip $(C_DEPS)),)
+-include $(C_DEPS)
+endif
+endif
+
+# Add inputs and outputs from these tool invocations to the build variables 
+
+# All Target
+all: sonic-dhcpmon
+
+# Tool invocations
+sonic-dhcpmon: $(OBJS) $(USER_OBJS)
+	@echo 'Building target: $@'
+	@echo 'Invoking: GCC C Linker'
+	$(CC) -o "$(DHCPMON_TARGET)" $(OBJS) $(USER_OBJS) $(LIBS)
+	@echo 'Finished building target: $@'
+	@echo ' '
+
+# Other Targets
+install:
+	$(MKDIR) -p $(DESTDIR)/usr/sbin
+	$(MV) $(DHCPMON_TARGET) $(DESTDIR)/usr/sbin
+
+deinstall:
+	$(RM) $(DESTDIR)/usr/sbin/$(DHCPMON_TARGET)
+	$(RM) -rf $(DESTDIR)/usr/sbin
+
+clean:
+	-$(RM) $(EXECUTABLES)$(OBJS)$(C_DEPS) $(DHCPMON_TARGET)
+	-@echo ' '
+
+.PHONY: all clean dependents

debian/changelog

@@ -0,0 +1,5 @@
+sonic-dhcpmon (1.0.0-0) UNRELEASED; urgency=medium
+
+  * Initial release.
+
+ -- Tamer Ahmed <[email protected]>  Mon, 09 Dec 2019 12:00:00 -0700

debian/compat

@@ -0,0 +1 @@
+9

debian/control

@@ -0,0 +1,16 @@
+Source: sonic-dhcpmon
+Section: devel
+Priority: optional
+Maintainer: Tamer Ahmed <[email protected]>
+Build-Depends: debhelper (>= 8.0.0),
+               dh-systemd
+Standards-Version: 3.9.3
+Homepage: https://github.com/Azure/sonic-buildimage
+XS-Go-Import-Path: github.com/Azure/sonic-buildimage
+
+Package: sonic-dhcpmon
+Architecture: any
+Built-Using: ${misc:Built-Using}
+Depends: libexplain51,
+         libevent-2.0-5
+Description: SONiC DHCP Monitor

debian/rules

@@ -0,0 +1,3 @@
+#!/usr/bin/make -f
+%:
+	dh $@ --with systemd

objects.mk

@@ -0,0 +1,4 @@
+USER_OBJS :=
+
+LIBS := -levent -lexplain
+