Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 3 Jul 1996 23:00:24 -0400 | From | "Theodore Y. Ts'o" <> | Subject | Re: SCSI device numbering (was: Re: Ideas for v2.1 |
| |
Date: Wed, 03 Jul 96 15:09:19 PDT From: Craig Milo Rogers <rogers@isi.edu>
I've also had SCSI peripherals that I've moved between systems (including laptops, thanks, David!), especially SCSI hard drives. I manually run a script to adjust the mount points to the hard drive I've plugged in. I've considered putting an easily-read volume label file in each of my partitions ("VOLUME.SYS"? ".volume"?) to automate mount point selection.
Stephen and I have been planning to add an 128-bit universally unique ID (UUID) in the ext2 superblock to help automate this process. It's also useful for his "supermount" for detecting when a removeable disk has really been changed.
How do you generally a globally unique UUID? Simple. Generate a 128 bit UUID as follows:
32 bits tv_sec of volume creation 32 bits tv_usec of volume creation 32 bits IP address of host which created the volume, or a random number if not available 32 bits random number
The basic idea of globally unique ID's is stolen from the DCE RPC, and its predecessor, the Apollo RPC. It's a nice way of picking a universally unqiue ID in a decentralized manner; while there's a chance you might have a collision, it's so small as to be virtually non-existent.
Obviously there would have to be a program to map the 128-bit UUID to the correct mount point, but that's best done in a user-mode program anyway.
- Ted
| ![\](/images/icornerr.gif) |