在 OpenWrt 经常看到这样的写法:

fit 你在做什么？fit 的定义在 include/image-commands.mk 中

define Build/fit         $(TOPDIR)/scripts/mkits.sh \                 -D $(DEVICE_NAME) -o $@.its -k $@ \                 -C $(word 1,$(1)) $(if $(word 2,$(1)),\                 $(if $(DEVICE_DTS_OVERLAY),-d $(KERNEL_BUILD_DIR)/image-$$(basename $(word 2,$(1))),\                         -d $(word 2,$(1)))) \                 $(if $(findstring with-rootfs,$(word 3,$(1))),-r $(IMAGE_ROOTFS)) \                 $(if $(findstring with-initrd,$(word 3,$(1))), \                         $(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE), \                                 -i $(KERNEL_BUILD_DIR)/initrd.cpio$(strip $(call Build/initrd_compression)))) \                 -a $(KERNEL_LOADADDR) -e $(if $(KERNEL_ENTRY),$(KERNEL_ENTRY),$(KERNEL_LOADADDR)) \                 $(if $(DEVICE_FDT_NUM),-n $(DEVICE_FDT_NUM)) \                 $(if $(DEVICE_DTS_DELIMITER),-l $(DEVICE_DTS_DELIMITER)) \                 $(if $(DEVICE_DTS_OVERLAY),$(foreach dtso,$(DEVICE_DTS_OVERLAY), -O $(dtso):$(KERNEL_BUILD_DIR)/image-$(dtso).dtb)) \                 -c $(if $(DEVICE_DTS_CONFIG),$(DEVICE_DTS_CONFIG),"config-1") \                 -A $(LINUX_KARCH) -v $(LINUX_VERSION)         PATH=$(LINUX_DIR)/scripts/dtc:$(PATH) mkimage $(if $(findstring external,$(word 3,$(1))),\                 -E -B 0x1000 $(if $(findstring static,$(word 3,$(1))),-p 0x1000)) -f $@.its $@.new         @mv $@.new $@ endef 

里面做了两件事情：

• scripts/mkits.sh 生成 .its
• mkimage 生成 fit

实例展开如下：

/home/my/openwrt/scripts/mkits.sh -D my -o /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin.its -k /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin -C none   -d /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/linux-5.15.31/arch/riscv/boot/dts/allwinner/my.dtb   -a 0x40200000 -e 0x40200000    -c "config-1" -A riscv -v 5.15.31 

mkimage  -f /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin.its /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin.new 

用法如下：

lql@debian:~/my/openwrt$ ./scripts/mkits.sh  Usage: mkits.sh -A arch -C comp -a addr -e entry -v version -k kernel [-D name -n address -d dtb] -o its_file         -A ==> set architecture to 'arch'         -C ==> set compression type 'comp'         -c ==> set config name 'config'         -a ==> set load address to 'addr' (hex)         -e ==> set entry point to 'entry' (hex)         -f ==> set device tree compatible string         -i ==> include initrd Blob 'initrd'         -v ==> set kernel version to 'version'         -k ==> include kernel image 'kernel'         -D ==> human friendly Device Tree Blob 'name'         -n ==> fdt unit-address 'address'         -d ==> include Device Tree Blob 'dtb'         -r ==> include RootFS blob 'rootfs'         -H ==> specify hash algo instead of SHA1         -l ==> legacy mode character (@ etc otherwise -)         -o ==> create output file 'its_file'         -O ==> create config with dt overlay 'name:dtb'                 (can be specified more than once) 

脚本理解：

#!/bin/sh # # Licensed under the terms of the GNU GPL License version 2 or later. # # Author: Peter Tyser <ptyser@xes-inc.com> # # U-Boot firmware supports the booting of images in the Flattened Image # Tree (FIT) format.  The FIT format uses a device tree structure to # describe a kernel image, device tree blob, ramdisk, etc.  This script # creates an Image Tree Source (.its file) which can be passed to the # 'mkimage' utility to generate an Image Tree Blob (.itb file).  The .itb # file can then be booted by U-Boot (or other bootloaders which support # FIT images).  See doc/uImage.FIT/howto.txt in U-Boot source code for # additional information on FIT images. # 

脚本的开头说明了一切:

• fit 是指 Flattened ImageTree (FIT)
• mkits.sh目的是生成 Image Tree Source (.its file)
• .its 文件是给 mkimage 用于生成 Image Tree Blob (.itb file)
• 更多关于FIT请看u-boot 源码中的 doc/uImage.FIT/howto.txt

生成的目标文件 .its 如下：

关于 mkimage ， 并不陌生，常规用法如下，用于生成 uImage

define Build/uImage
        mkimage \
                -A $(LINUX_KARCH) \
                -O linux \
                -T kernel \
                -C $(word 1,$(1)) \
                -a $(KERNEL_LOADADDR) \
                -e $(if $(KERNEL_ENTRY),$(KERNEL_ENTRY),$(KERNEL_LOADADDR)) \
                -n '$(if $(UIMAGE_NAME),$(UIMAGE_NAME),$(call toupper,$(LINUX_KARCH)) $(VERSION_DIST) Linux-$(LINUX_VERSION))' \
                $(if $(UIMAGE_MAGIC),-M $(UIMAGE_MAGIC)) \
                $(wordlist 2,$(words $(1)),$(1)) \
                -d $@ $@.new
        mv $@.new $@
ende

mkimage -h 查看 usage

lql@debian:~/my/openwrt$ mkimage -h
mkimage: invalid option -- 'h'
Error: Invalid option
Usage: mkimage -l image
          -l ==> list image header information
       mkimage [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image
          -A ==> set architecture to 'arch'
          -O ==> set operating system to 'os'
          -T ==> set image type to 'type'
          -C ==> set compression type 'comp'
          -a ==> set load address to 'addr' (hex)
          -e ==> set entry point to 'ep' (hex)
          -n ==> set image name to 'name'
          -d ==> use image data from 'datafile'
          -x ==> set XIP (execute in place)
       mkimage [-D dtc_options] [-f fit-image.its|-f auto|-F] [-b <dtb> [-b <dtb>]] [-i <ramdisk.cpio.gz>] fit-image
           <dtb> file is used with -f auto, it may occur multiple times.
          -D => set all options for device tree compiler
          -f => input filename for FIT source
          -i => input filename for ramdisk file
Signing / verified boot not supported (CONFIG_FIT_SIGNATURE undefined)
       mkimage -V ==> print version information and exit
Use -T to see a list of available image types

这里我们看到另一种用法：用 -f 指定 FIT 文件 。

mkimage  -f /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin.its /home/my/openwrt/build_dir/target-riscv64_riscv64_musl/linux-sunxid1/my-kernel.bin.new

输入文件和各项参数都在 .its 中指定了。 相比第一种用法，更适用于多个文件的拼接。