Re: Large device numbers (was Re: disk naming proposal & devfs)

Dan Taylor (
Sat, 17 Jan 1998 21:13:06 -0600 (CST)

You are also correct. It is being implemented as a solution to
just about any problem presented in the current system. See
Richards FAQ on the topic for the definitive view, he is writing
the code after all.

I just happen to know which solutions interest me most.

On Tue, 13 Jan 1998, Ian Burrell wrote:

> >
> > Various problems related to the current indirect device referencing
> > scheme, including (but not necessarily limited to):
> > -8bit minors,
> > -major/minor table lookup times
> > -filesystem rewriting necessary to go to 16 or 32 bit minors.
> > -major number conflict resolution
> >
> I thought devfs was a solution to the problems of large directories
> and dynamic creation of device files. There really should be a common
> system for going from device number to device that is independent of
> whether it is an on-disk device node or purely virtual inode. The
> device registration could be made distinct from the inodes and
> directories entry in devfs and normal devices nodes. Opening a file
> goes filename -> dentry -> inode -> dev_t -> device. A new lookup
> would be needed for dev_t to device driver.
> The easy way to split 64-bit device numbers in half and use the 32-bit
> major number to identify the device driver and the 32-bit minor number
> used to identify the specific device. Drivers would register
> themselves with the driver table, and the minor number and canonical
> name with device table/devfs.
> A better way might be use the entire 64-bit value as the device id and
> scrap the major/minor separation. Then the driver is identified by
> variable-length prefix. Overlapping drivers could be accomplished
> with a longest-matching-prefix search. This would be inefficient but
> could be speeded up by caching the resolved devices in inodes.
> - Ian
> --
> -- Ian Burrell == **
> <URL:>
> All programmers are playwrights and all computers are lousy actors.