The standard LEAF/LRP kernel requires two patches:
initrd_archive. This permits the use of a tar.gz archive instead of the standard gzipped filesystem archive.
linuxrc_always. This runs the /linuxrc script no matter what happens.
Since the loading mechanism is changing, and support for these scripts are waning, it is beneficial to convert LEAF projects so that they do not require these patches.
During the boot process, Linux can use a RAM disk to bootstrap the system. A typical use for the RAM disk is to load SCSI modules and drivers to boot a SCSI disk. The LEAF usage of the initial RAM disk is not typical.
Here is how Linux uses the RAM disk and /linuxrc during the boot process:
Load the filesystem image (typically initrd.gz or similar)
Is the boot device /dev/ram0? If so, don't run /linuxrc.
Once /linuxrc is running, it must perform the following steps:
Create a root filesystem. This probably should be another RAM disk to avoid problems with how the Linux kernel uses /dev/ram0.
Create (in the new root) a directory /initrd if you want to preserve the initial filesystem after the kernel is done booting. This is mainly useful for debugging and curiosity.
Dismount nearly all filesystems. This does not include /proc and / in the initrd environment; it does include the new root and everything underneath it.
Exit from /linuxrc. The kernel should switch from the initrd root volume to the new created root volume.
Once /linuxrc is done, the system must still mount all volumes. Due to the nature of the original LEAF systems, this was not necessary. However, it is necessary here since /linuxrc requires dismounting of all system volumes in order to perform the root volume switch (otherwise known as "pivot root").