Initrdrewrite

The current incarnation of mkinitrd sucks for a variety of reasons. This page documents some of the plans to replace it with something better. This is not yet a feature, it's currently just a playground to try some things out

Planning

Initial ideas

• One initrd to rule them all - Instead of one for the livecd, one for the installer, one for the distro
• Death to nash - The bits of nash that don't currently exist in other tools need factoring out and putting into util-linux or similar packages.
• Same bits - Use the same bits the rest of the distro uses instead of custom functionality. No custom udev, just use the regular one etc.
• Diagnostics - Include a shell for diagnostic/debugging purposes.
• Probe at runtime instead of buildtime - Include all drivers, not just the drivers necessary for the hardware being run. (For storage, the common ones will be built-in to the kernel anyway)
• The initrd will be usable on other distros. - The idea being that it can be included in the upstream kernel, and changed when kernel interfaces change etc to prevent breaking distros.

Major Cases

The first cut of this will just support the simple case of root on a hard disk. Eventually we want to support the numerous esoteric cases the existing initrd supports. Namely root on..

• Disk based devices
  • -on-lvm
  • -on-dm-crypt
  • -on-dmraid
  • -on-mdraid
  • -on-multi-path
• Network based devices
  • -on-iSCSI
  • -on-nfs
  • -on-nbd
• Special cases to revisit later:
  • livecd (/ on dm-snapshot over ext3 on squashfs on iso9660)
  • installer
  • kdump

Other tasks performed by the initrd other than mounting rootfs

• restore from hibernate
• start 'pretty' plymouth
• kdump
• Loading initial SELinux policy.
• RFE: run ssh server to enter crypto password or perform debugging

Utilities to include in the initrd

• libc
• udev
• switchroot
• bash (no nash!)

Other stuff

• The code in the kernel for creating minimal initramfs's (scripts/gen_initramfs_list.sh & usr/*) is kind of useless. It's probably for the best if this just goes away and gets replaced by something useful.
• Make it possible to easily extend the initramfs, e.g. by packages that provide additional features to the initramfs, e.g. an ssh server

Bits

Stay tuned...