We have some PPC440GX based blade servers that boot from flash. My boss wants me to add additional checksums somewhere in the JFFS2 partitions as an overall check of the JFFS2 filesystem images that we burn to flash. Once the image is burned, that file system is never written to again. (That's the theory anyway). So every time they boot they want to read these checksum out of the flash and use it to decide if they want to/can boot with that filesystem or fallback to another one. Each copy of the kernel has its own JFFS2 partition. The root file system has its own JFFS2 partition. I don't understand why they don't just write everything to one JFFS2 partition. They say it is because they are worried about power failure while writing to the flash and want to isolate any write failures. ( I tried to tell them that the journaling already handles that case quite well - but they are non-believers) Some questions; 1) Is a filesystem-wide checksum really necessary or is it kind of silly? 1.1) Doesn't JFFS2 already do some integrity checking after it finishes writing a file? Are there checksums or anything that serves the same function? They want to avoid having to checksum the entire filesystem at boot time (due to quick boot time requirements) - is there some field or fields, or technique that can quickly tell me if the filesystem is ok? 2) Is there any place within the bounds of a JFFS2 partition that is safe from being overwritten? before and after checksums could be placed there. 2.1) Is there any way to create such a place? for example, by appending the checksums to the end of some filesystem-wide structure like a super block? Or maybe it can be hidden in a couple of inodes that are never overwritten. What I'm looking for regarding this adding extra checksums into the JFFS2 image is: 3.1) How can it be done? 3.2) Why might it be unnecessary or even inadvisable? 3.3) Why can't it be done? Once I understand the answers to these questions I can go back and see what they want to do. In the meantime, I am dumping and analyzing the JFFS2 filesystems we have and reading the code trying to find the answers. thanks for your time. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://ozlabs.org/pipermail/linuxppc-embedded/attachments/20051019/8515b9ab/attachment.htm
