How can I recreate ArchLinux's installation ramdisk?

Question

Hi,
I'm on a project where I developed my own custom ramdisk so I can automate the installation procedure for Arch. Currently, I have a script that takes Arch's initrd.img, and adds stuff to it (my scripts).
Now, I would like to be able to create the ramdisk from scratch (not requiring Arch's image as a base). Therefore, I would like to get the script(s) (if any) that ArchLinux devs use to create Arch's installation ramdisk. There are some things I want to change (some busybox options and stuff) so I really need this.
On cvs I can see a nice laid build system for creating an installation image using the new cpio method. But I can't find anything related to the old initrd system (even when using the RELEASE_0_7_2 CVS tag).
Also, I'm interested in the initcpio system since it seems way more simple to create Arch's installation image. Even more, I already saw the archboot package that would allow me to recreate the initcpio that will be used for installing the upcoming Arch release. I'm going to play with this, but I'm going to stay with the old initrd system until Arch's next release.
And regarding the cpio system, I have a doubt. How does the ramdisk environment change when using cpio over old initrd? I noticed that busybox is no longer used. Is using busybox an option? Would it make sense?
Thanks

Answer 1

V01D wrote:Ok, now I'm getting things a little better. I think that my best option is to use busybox using initcpio (don't you know how I can ask about the scripts you use for the old initrd? even if I don't use that initrd, I would like to see how the filesystem inside the initrd is created; there are programs like dhcpcd that I don't know from where to take (my own system?)).
Well, the scripts would/should work with either system.  Problem is that the initrd scripts are a bit lacking.  The mkinitcpio scripts are included in /lib/initcpio/* - check under the "hooks" directory.  You don't need dhcpcd.  This is already accounted for with the 'net' hook, which is part of mkinitcpio. 
mkinitcpio -H net
for help with the net hook, and how to use it.
V01D wrote:You say I should use static busybox or with klibc. Can't I just use uClibc? (NOTE: I get a little confused about what uClibc is... I see libc6 on the ramdisk, is that uClibc?)
Both uClibc and klibc have similar goals.  Both are mini C libraries, meant to be used for small systems.  The difference is that uClibc is meant for embedded systems, and klibc is meant specifically for early-userspace.  You *can* use a pure uClibc system, but you will lose all the tools that klibc provides (ls /usr/lib/klibc/bin/*).  Admittedly, some of these are replaced by busybox, but others (which are important) may not be.  However, they should all compile under uClibc.
V01D wrote:is the new cpio system just a new way of handling file and a RAM based filesystem? or is it a deeper change compared to initrd? the whole thing about kinit confuses me a little... And I can't find much documentation about this. I mean, I saw an option on busybox's config regarding something about init and initramfs, but I don't get much about it.
In other words, how much would I have to change If I'd create a cpio with all files that are present on the initrd?
The difference between initrd and initramfs, from a consumer's persepctive, is minimal.  Instead of /linuxrc, you want to use /init as the script name.  If you were to convert the existing initrd, you would just have to rename that.
I need to stress, though, that the linuxrc for the old initrd is very very limited.  Reusing that is going to cause alot of headaches and cost you development time.  The init script and hooks that are part of mkinitcpio are much more generalized, and the system, as a whole, is hugely open to "add ins".  Maybe it would help if you explained exactly what you want to do, and I can tell you how much work it would take to do it both ways?
V01D wrote:regarding any extra program I want to add (think of the BINARY='' option of mkinitcpio), how would this be handled if I use busybox? will it see that I use uClibc? Or will it try to add klibc?
klibc is added by the 'base' hook, which is why I stated earlier that you can rewrite your own custom base hook to take care of that, or even removed base altogether.  There are only a few minor issues there.
V01D wrote:Can I add any program to the ramdisk and expect it to work (assuming it doesn't depends on any other library but libc)? I mean, does a program have to be compiled specially to be used with uClibc or klibc?
No, copying random programs to the ramdisk will fail.  You need to recompile them against klibc or uClibc, or link them statically.  You can not interchange C libraries.
I really think it would help if you describe what you're trying to do.  It sounds like you want busybox simply for convienance, and are going to cause yourself a mess of trouble just to add it.