kernel: set root on NFS when enabled

Replace the configured root device with a NFS root device and automatic
IP configuration for booting over NFS.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

SVN-Revision: 48591

include/kernel-defaults.mk

@@ -104,6 +104,18 @@ define Kernel/SetNoInitramfs
 	echo 'CONFIG_INITRAMFS_SOURCE=""' >> $(LINUX_DIR)/.config.set
 endef
 
+ifeq ($(CONFIG_KERNEL_ROOT_NFS),y)
+  define Kernel/SetNfsCmdline
+	rm -f $(LINUX_DIR)/.config.prev
+	mv $(LINUX_DIR)/.config $(LINUX_DIR)/.config.old
+	grep -v "CONFIG_CMDLINE=" $(LINUX_DIR)/.config.old > $(LINUX_DIR)/.config
+	grep "CONFIG_CMDLINE=" $(LINUX_DIR)/.config.old | cut -d\" -f2 | sed 's/root=\/dev\/\([a-z0-9]*\)\(.*\)/CONFIG_CMDLINE=\"root=\/dev\/nfs ip=dhcp\2\"/' >> $(LINUX_DIR)/.config
+  endef
+else
+  define Kernel/SetNfsCmdline
+  endef
+endif
+
 define Kernel/Configure/Default
 	$(LINUX_CONF_CMD) > $(LINUX_DIR)/.config.target
 # copy CONFIG_KERNEL_* settings over to .config.target
@@ -114,6 +126,7 @@ define Kernel/Configure/Default
 	$(SCRIPT_DIR)/metadata.pl kconfig $(TMP_DIR)/.packageinfo $(TOPDIR)/.config $(KERNEL_PATCHVER) > $(LINUX_DIR)/.config.override
 	$(SCRIPT_DIR)/kconfig.pl 'm+' '+' $(LINUX_DIR)/.config.target /dev/null $(LINUX_DIR)/.config.override > $(LINUX_DIR)/.config.set
 	$(call Kernel/SetNoInitramfs)
+	$(call Kernel/SetNfsCmdline)
 	rm -rf $(KERNEL_BUILD_DIR)/modules
 	cmp -s $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev || { \
 		cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config; \