Support for RHEL8 (#10)

* Support for RHEL8

* Enhanced Makefile for RHEL8

* Updated README.md

* Remove unused KVERSION variable from Makefile

Makefile

@@ -1,30 +1,53 @@
+
+RHEL8 := $(shell cat /etc/redhat-release 2>/dev/null | grep -c " 8." )
+ifneq (,$(findstring 1, $(RHEL8)))
+	RHEL8FLAG := -DRHEL8
+endif
+
 PWD := $(shell pwd) 
-KVERSION := $(shell uname -r)
-INCLUDE_DIR = /usr/src/linux-headers-$(KVERSION)/
+
+ifeq ($(KVER),)
+		KVER := $(shell uname -r)
+	endif
+
+ifneq ($(RUN_DEPMOD),)
+		DEPMOD := /sbin/depmod -a
+	else
+		DEPMOD := true
+	endif
+
+ifeq ($(KDIR),)
+		KDIR := /lib/modules/$(KVER)/build
+	endif
+
 
 CONFIG_MODULE_SIG=n
 MODULE_NAME = gtp5g
 
-MY_CFLAGS += -g -DDEBUG
+MY_CFLAGS += -g -DDEBUG $(RHEL8FLAG)
 EXTRA_CFLAGS += -Wno-misleading-indentation -Wuninitialized
 CC += ${MY_CFLAGS}
 
 obj-m := $(MODULE_NAME).o
 
-all:
-	make -C $(INCLUDE_DIR) M=$(PWD) modules
+MOD_KERNEL_PATH := /kernel/drivers/net
+
+default: module
+
+module:
+	$(MAKE) -C $(KDIR) M=$(PWD) modules
 clean:
-	make -C $(INCLUDE_DIR) M=$(PWD) clean
+	$(MAKE) -C $(KDIR) M=$(PWD) clean
 
 install:
+	$(MAKE) -C $(KDIR) M=$$PWD INSTALL_MOD_PATH=$(DESTDIR) INSTALL_MOD_DIR=$(MOD_KERNEL_PATH) modules_install	
 	modprobe udp_tunnel
-	cp $(MODULE_NAME).ko /lib/modules/`uname -r`/kernel/drivers/net
-	depmod -a
+	$(DEPMOD)
 	modprobe $(MODULE_NAME)
 	echo "gtp5g" >> /etc/modules
 
 uninstall:
-	rmmod $(MODULE_NAME)
-	rm -f /lib/modules/`uname -r`/kernel/drivers/net/$(MODULE_NAME).ko
-	depmod -a
+	rm -f $(DESTDIR)/lib/modules/$(KVER)/$(MOD_KERNEL_PATH)/$(MODULE_NAME).ko
+	$(DEPMOD)
 	sed -zi "s/gtp5g\n//g" /etc/modules
+	rmmod -f  $(MODULE_NAME)

README.md

@@ -4,7 +4,7 @@ For detailed information, please reference to 3GPP specification TS 29.281 and T
 
 ## Notice
 Due to the evolution of Linux kernel, this module would not work with every kernel version.
-Please run this module with kernel version `5.0.0-23-generic` or upper than `5.4` (Ubuntu 20.04).
+Please run this module with kernel version `5.0.0-23-generic`, upper than `5.4` (Ubuntu 20.04) or RHEL8.
 
 Please check the [libgtp5gnl](https://github.com/free5gc/libgtp5gnl) version is the same as gtp5g,
 because the type translating between libgtp5gnl and gtp5g had been changed.
@@ -41,6 +41,8 @@ The gtp5g interface will be created by using libgtp5gnl scripts
     + Note: It will delete list of rules and interface
 
 ## Change Log
+### v0.2.1
++ Support for RHEL8
 ### v0.2.0
 + Changed to host type between gtp5g and libgtp5gnl
 + Supported forwarding policy feature, but need to set ip rule and ip route with Linux mark by self

gtp5g.c

@@ -1184,7 +1184,7 @@ static struct rtable *ip4_find_route(struct sk_buff *skb, struct iphdr *iph,
 		mtu = dst_mtu(&rt->dst);
 	}
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 4, 0)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 4, 0) || defined(RHEL8)
        rt->dst.ops->update_pmtu(&rt->dst, NULL, skb, mtu, false);
 #else
        rt->dst.ops->update_pmtu(&rt->dst, NULL, skb, mtu);