Thursday, October 15, 2009


When DGOS boots, it has no filesystem or device drivers. This is a problem since the filesystem and block device drivers are modules - files on the filesystem. We are thus left with a chicken-and-egg scenario that we need the filesystem access to load modules and we need the filesystem modules to have filesystem access. This is solved using initfs. This is a simple flat filesystem in ram that has just the bare minimum modules required to bring up the filesystem and device support needed to load the rest of the system. The bootloader loads two files to RAM. The kernel and the initfs image. The kernel then uses the initfs image to load the modules needed to access the main filesystem. initfs memory is then freed, and with this new ability to read the filesystem the kernel can go on booting.

DGOS used to have a very simple initfs FS and init_blk block device in it. I decided to replace initfs with just FAT, since it is simple, and there is little harm in compiling it into the kernel. This also means that the initfs image for most devices will now contain just one module - the block device driver for SD card (or in the case of lifedrive - two: SD and HDD drivers). FAT driver will now be part of the kernel and thus doesn ot need to be a module in initfs.