22 openwrt uses external kernel and kernel_ config

Because the kernel should be modified by typing patch The way will be more troublesome , Sometimes we will extract the kernel directly and modify the source code , At this time, you need to use external kernel This option of .openwrt The kernel of config It is saved according to the version , Such as config-4.19, When we have many and hardware platforms in one version , platform config It is very important to classify and save , At this time, we will choose to use external kernel_config The way .

1、 External use kernel

Using external kernel source code , We will compile it again openwrt, And then build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7622/linux-4.19.81/ Copy source code to , Such as …/extkernel/4.4.198 Under the table of contents .

then make menuconfig Turn on Use external kernel tree Options can be .

[*] Advanced configuration options (for developers)  ----
    (../extkernel/4.4.198) Use external kernel tree

2、 External use kernel config

The kernel configuration to be modified is , We will use make kernel_menuconfig To configure .

2.1 The original way

First look at the original kernel .config The generative logic of ,make kernel_menuconfig When , Will pass kconfig.pl The script will generic and mediatek Under the config-4.19 Merge into one .config For kernel use .

/home/19.07/scripts/kconfig.pl  + /home/19.07/target/linux/generic/config-4.19 /home/19.07/target/linux/mediatek/mt7622/config-4.19 > /home/19.07/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7622/linux-4.19.81/.config

When we kernel_menuconfig After configuration , It will be saved and used when exiting kconfig.pl The script saves the configuration file again to config-4.19 In file .

/home/19.07/scripts/kconfig.pl '>'  /home/19.07/target/linux/generic/config-4.19 /home/19.07/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7622/linux-4.19.81/.config > /home/19.07/target/linux/mediatek/mt7622/config-4.19

So what we need to do is to report everywhere and import process , Change to our own configuration kernel_config file .

2.2 Use external customization kernel config The way

stay config/Config-devel.in Add inside KERNEL_CONFIG The option of supports external configuration

      config EXTERNAL_KERNEL_TREE
         string "Use external kernel tree" if DEVEL
         default ""
 
+     config EXTERNAL_KERNEL_CONFIG
+         string "Use external kernel config" if DEVEL
+         default "

then make menuconfig Fill in the path name of the external configuration file we want to use

[*] Advanced configuration options (for developers)  ----
    (./userconfig/BOARD1-kernel.config) Use external kernel config

Here we need a copy of the kernel .config file , The first time is usually after we want to compile , Copy it and rename it as ours BOARD1-kernel.config

Modify the import process , stay 19.07/include/target.mk Add import external kernel config Content

 #
 # 
 # Support external kernel config
 #
 ifneq ($(call qstrip,$(CONFIG_EXTERNAL_KERNEL_CONFIG)),)
   EXT_KERNEL_CONFIG_FIRST_CHAR := $(shell path=$(CONFIG_EXTERNAL_KERNEL_CONFIG); echo $${path:0:1})
   ifeq ($(EXT_KERNEL_CONFIG_FIRST_CHAR),/)
     _EXT_KERNEL_CONFIG_PATH := $(CONFIG_EXTERNAL_KERNEL_CONFIG)
   else
     _EXT_KERNEL_CONFIG_PATH := $(TOPDIR)/$(CONFIG_EXTERNAL_KERNEL_CONFIG)
   endif
   LINUX_CONF_CMD := cat $(_EXT_KERNEL_CONFIG_PATH)
   LINUX_RECONF_CMD := $(LINUX_CONF_CMD)
 else
   LINUX_CONF_CMD = $(call __linux_confcmd,$(LINUX_KCONFIG_LIST),)
   LINUX_RECONF_CMD = $(call __linux_confcmd,$(LINUX_RECONFIG_LIST),)
   LINUX_RECONF_DIFF = $(call __linux_confcmd,$(filter-out $(LINUX_RECONFIG_TARGET),$(LINUX_RECONFIG_LIST)),'>')
 endif

Modify the saving process ,19.07/include/kernel-build.mk Add and save external kernel config Content

 ifneq ($(strip $(CONFIG_EXTERNAL_KERNEL_CONFIG)),"")
 	cp -a $(LINUX_DIR)/.config $(_EXT_KERNEL_CONFIG_PATH)
 else
 	$(LINUX_RECONF_DIFF) $(LINUX_DIR)/.config > $(LINUX_RECONFIG_TARGET)
 endif

after , Again make kernel_menuconfig You can see that , The import process is as follows ：

cat /home/19.07/"./zhconfig/BOARD1-kernel.config" > /home/19.07/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7622/linux-4.19.81/.config

The preservation process is as follows ：

cp -a /home/19.07/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7622/linux-4.19.81/.config /home/19.07/"./zhconfig/BOARD1-kernel.config"