[Sussex] kernel 2.6

[Steve Dobson]

Morning Thomas

On Fri, Mar 19, 2004 at 08:13:17AM +0000, Thomas Adam wrote:
>  --- Steve Dobson <steve at dobson.org> wrote: 
> 
> > However, will upgrading my laptop I did read that "devfs" is not 
> > "OBSOLETE" and is being replaced by udev.  This might be causing
> > some/all
> > of your problems.  Are you running devfs and devfsd?  If
> 
> It doesn't look as though he is, Steve. Typically devfs device names look
> like:
> 
> /dev/ide/disk0/channel1/part1

Yes, I know.  But IIRC he just gave us the data in /etc/fstab.  I'm running
devfs[d] and my fstab looks the same as I still use the old /dev/hd[abcd][1-8]
symlinks in my fstab.  That's a hang over since my 2.2/2.4 swap-over days.  I
suppose I should change over, but... :-)

> > udev (http://www.kernel.org/pub/linux/utils/kernel/hotplug/) is changing
> > the way that the kernel handles devices.  The device namespace and major
> > number space (with the growth of USB devices and large SCSI systems) is 
> > not coping and work is afoot to remove the information to userland where
> > it belongs.
> 
> Udev has been in existance for some time now. Of course, I am no fan of
> udev or its kindred, and as such am sticking with a static /dev tree.
> What's that? Major/minor numbers? heh, I mknod up and down...

That is fine for "small" systems, but for those really, really, really big
systems with very large numbers of SCSI devices that are now coming on line.
It is not unknown for 4K SCSI disks to be connected.  With only an eight-bit
minor number you have to start poaching "spare" major numbers.

Now with a lot of devices coming on line (mostly USB) we are now in a
position where there are more types of device than there are major numbers.
To see the other problems read:
http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev_vs_devfs

The problem with Linux is that it scales from the very small, embedded, system
to mainframes.  It is necessary, therefore, for the kernel to cope with both
extreams.  devfs pushed some user-land information down into the kernel -
which is a bad thing.  The udev/hotplug allows both for a very large number
of devices as well as a very large number of device instances as major, as
well as minor, numbers can be assigned on the fly.

I also like the idea the /dev only contains files for devices that really
are connected to a system.  Not all possible devices that could be connected.

That's my 2p worth for what it is worth [about half the face value :-)]

Steve D