Re: Poor device management

Richard Gooch (Richard.Gooch@atnf.CSIRO.AU)
Tue, 19 May 1998 18:08:11 +1000

John Goerzen writes:
> I would like to address the topic of naming of devices. Currently, we
> have two serious problems:

I agree.

> 1. It appears that Linux can support a maximum of 16 SCSI hard drives
> per system, according to devices.txt.
> This is a serious issue as we would like to have more than that on
> some machines but the OS does not appear to support that. The
> allocated block of device numbers appears to have no support for more.

Jakub did something with the VGER tree to support many SCSI discs. I
think it required some new system calls (to deal with larger device
numbers). There is a technique you could implement using devfs which
doesn't require new system calls (see the devfs FAQ).

> 2. Device numbers can change between boots or even during operation.
> This is because the device numbers (and thus, /dev entries) are
> allocated in sequential order. Thus, for instance, if my Jaz drive
> (SCSI ID 4) is turned off but my scanner (ID 5) is on, the scanner
> gets a particular device assigned to it. However, it the Jaz drive is
> on when the system boots, the Jaz gets that ID and the scanner gets
> something different.
> It would, therefore, be highly advisable to go to something akin to
> Solaris -- the /dev entries specify controller, target, and LUN
> expliticly. This will remove a lot of confusion especially
> surrounding the sg devices and eliminate the problem of drifting
> device entries.

This (point (2)) is already done: it's called devfs. Check out:

and navigate to my kernel patches for 2.1. There you'll see links to
the devfs patch and the devfs FAQ.



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