On Mon, Jan 9, 2012 at 3:41 AM, Jan Steffens <jan.steffens@xxxxxxxxx> wrote: > On Mon, Jan 9, 2012 at 4:58 AM, Jonathan Vasquez <jvasquez1011@xxxxxxxxx> wrote: >> Hello everyone, >> >> So I've been experimenting on removing my use of initrd and using the >> kernel directly. >> >> My current setup is the following: >> >> GPT, LVM, GRUB2 (So I can boot my partitions that are inside the LVM). >> >> /dev/sda1 BIOS Boot Partition EF02 (GPT) >> /dev/sda2 Linux LVM (named arch) >> >> /dev/arch/boot - /boot >> /dev/arch/swap - swap >> /dev/arch/home - /home >> /dev/arch/root - / >> >> When I compiled my custom kernel (from upstream, and yes I did enable >> device mapper support compiled into the kernel, I've also experimented >> with it as a module), the kernel fails to see the / partition. >> >> So I turn on my computer, BIOS starts, then GRUB2 starts, GRUB2 sees >> the /boot partition inside of the `arch` lvm because GRUB2 has support >> for it (insmod lvm), then when the kernel (which is inside the /boot >> partition inside the lvm) starts, the kernel "loses" the ability to >> find the partitions inside of the lvm. Which leads me to believe that >> GRUB2's ability to see lvm partitions doesn't carry over to the >> kernel.. rightfully so, 2 seperate applications. Then the kernel >> panics and says that I need to set the correct root= parameter. The >> parameter is set but the parameter is /dev/arch/root .. a partition >> inside of the lvm which the kernel cannot see after GRUB2 boots the >> kernel. >> >> I'm assuming this is why we need an initrd. So that the /init script >> inside the initrd does what it needs (like `vgchange -a y` then >> mounting /dev/arch/root as newroot and transferring control back to >> the kernel with that new root parameter). >> >> I guess what I need to do is rethink my partition layout because I >> cannot see a way to boot my root LVM partition without initrd, without >> doing a few things. >> >> Here is a few drawings I've made to think about my layout: >> >> (Current Layout) >> http://farm8.staticflickr.com/7016/6664419375_2ee9a7b794_b.jpg >> >> (Pondering Sheet) >> http://farm8.staticflickr.com/7168/6664367587_6ca149cfb3_b.jpg >> >> As you can see in the second sheet, my thoughts are as follows: >> >> Scenario 1. GRUB 2 starts, it finds /boot inside of the lvm, that then >> triggers the kernel to start, which then finds the root partition that >> is on a regular partition on the hdd, therefore no dm-mod support >> needs to be compiled directly into the kernel or to use an initrd to >> set up the environment before hand, after that happens, the init >> scripts (also /etc/fstab) load up dm-mod and load up /home which is >> inside of the lvm as well. >> >> Scenario 2. GRUB 2 starts, it finds /boot which is now on a normal >> partition, that then triggers the kernel which also finds / on a >> normal partition as well, and then the kernel triggers the systems >> init scripts, and loads up all the other partitions back into the / >> filesystem layout. >> >> The point of the above set up is to minimize real partition usage, and >> maximize lvm usage for the benefits of flexibility (involving >> resizing, shrinking, and adding more space) without the need for >> initrd. In term simplifying the entire system. >> >> There are of course other ways to simplify the system, and I'm not >> against using initrd in any way, but it's something that I would not >> want to use, or learn not to be dependent on. >> >> -- >> Jonathan Vasquez > > If you're not against initrd, then just keep using it. It's the > standard way of booting, not evil, and here to stay. The kernel alone > just isn't smart enough to boot from much more than a simple root > partition. And if it's modularized like our stock kernel, can't boot > alone at all (due to missing drivers). > > By the way, my current setup is as follows: > sda (GPT) > - sda1: EFI System Partition (FAT), contains GRUB2, mounted at /boot > - sda2: swap > - sda3: Btrfs, mounted at / > > Having grub and the kernels on the same partition simplifies the grub > configuration quite a bit. I guess my adventure to boot / without initrd has come to an end.. -_- I was studying the mkinitcpio code.. I have to say, shoutouts to the 4 devs.. you did a great job, my code would not even be close to that. -- Jonathan Vasquez
