On Sat, Mar 27, 2021 at 5:43 PM Joshua Kinard <ku...@gentoo.org> wrote: > > I kinda wish the Linux kernel had an ability to partially boot, init the > networking subsystem, then fetch an initramfs image over TFTP like it can do > with NFS Root. That would solve the problem on my MIPS system(s) (and make > install netboots better). I've dug around, but this does not seem to be a > capability currently in the kernel, unless I have over looked something.
Support exists, in the form of an initramfs. Bear with me for a second. An initramfs does not need to be large. It is just software. Sure, they're often implemented in bash with all sorts of userspace tools in the image, and that uses lots of space. However, an initramfs could be nothing but a small compiled binary and nothing else - a few kilobytes even. I'm not aware if anything like this has already been created, but you could do something reminiscent of coreboot, and it would be distro-agnostic. Just build a minimal kernel with only support for whatever you need to read a kernel and initramfs (from disk, network, whatever). Then build an initramfs that minimally fetches that kernel - it could just be a tiny binary, or it could use tools like curl/etc. Then you'd kexec the new kernel/initramfs which would do the full boot, and this wouldn't have any size limitation. An initramfs is just a way to automate the kernel boot process using userspace code, vs needing to do a lot of fancy stuff in kernel space. They can get a bit bloated when you make them full-featured/generic, but if you just want a secondary bootloader you can shrink both the kernel and the initramfs considerably, and use that to boot another kernel. If I were to look anywhere for something I could use out-of-the-box it would be with coreboot. That is a linux-based kernel/initramfs designed to be a bootloader really. -- Rich
