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This feature template enables support for initramfs. This file contains four parts:
1.What's initramfs
2.How to build it in Wind River Linux
3.How to use it in target board
1.What's initramfs
initramfs is an alternative, simpler method of having files available at boot time
without having them in a persistent mountable filesystem. It's linked in the kernel file
when compiling the kernel. So we can boot the target board only using the kernel with initramfs.
For more details, please refer to linux/Documentation/filesystems/ramfs-rootfs-initramfs.txt
2.How to build it in Wind River Linux
After configuring a BSP using Wind River Linux, following command will generate a kernel
with initramfs support:
#make boot-image BOOTIMAGE_FSTYPE=initramfs BOOTIMAGE_TYPE=flash
Then the file of "export/<BSP>-initramfs" will be the kernel with initramfs.
Because initramfs is designed for small filesystem, it's recommended to use glibc_small
and uclibc_small to configure a BSP. If using glibc_std or glibc_cgl, it may make the kernel
rather big and can't boot in the target board.
3.How to use it in target board
Because the kernel with initramfs already contains root filesystem, when booting the kernel,
we mustn't pass any "root=/dev/xxx"(xxx means nfs, hda1 etc.) to kernel cmdline, otherwise
the kernel won't use the initramfs as root filesystem. Besides this notice, booting the kernel
with initramfs doesn't need special steps.
It should be noted that on powerpc arch:
Because the kernel often needs dtb file loaded after 2MBytes space from the kernel loading address,
if the kernel size is larger than 2MByts, the kernel will overlap with the dtb, which will lead to
the kernel booting failure. Please modify loading address of the dtb file to fit the kernel size.
e.g.
The kernel size is 5MBytes, loading address of the kernel is 0x200000 and the
default dtb loading address is 0x400000. Then the dtb loading address will be
changed to 0x200000 + 0x500000(5MBytes) = 0x700000
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