Date: Wed, 3 Nov 2004 15:08:27 -0800
From: Greg KH <greg@kroah.com>
To: "Kilau, Scott" <Scott_Kilau@digi.com>
Cc: germano.barreiro@cyclades.com, linux-kernel@vger.kernel.org
Subject: Re: patch for sysfs in the cyclades driver
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On Wed, Nov 03, 2004 at 04:35:44PM -0600, Kilau, Scott wrote:
> 
> > Your driver can use whatever name you wanted, as long as it's the
> > LANNANA name that you asked for and were assigned.  We do have
> standards
> > for a good reason, and the kernel will follow them.
> 
> >That being said, have your customers use a tool like udev.  Then they
> > can name their tty devices whatever they want.  No limitations there
> at
> > all.
> 
> The problem is that LANANA assumes a product/driver
> may only have a few tty's, say up to maybe 256 or so.
> 
> For example, we have a driver that can support 1000s or 10000s of tty's.

Great, use udev for that.

> When dealing with that large amount of ttys, telling a customer
> that they should remember that a tty down in Austin TX is ttyD19234,
> and that the tty over in England is ttyD57267 is pretty ridiculous.

I agree, use udev.

> Our customers want to select a custom tty name base,
> as well as a custom tty port number...
> This way they can use logical names in an "area" specific range.

I agree, use udev.

> For example, maybe they have 10 16 port units in down in Texas,
> they may want to group them as /dev/ttytx000 to /dev/ttytx159,
> and the guy in england might want to name theirs
> /dev/ttyengland_a to /dev/ttyengland_h

Fine, have them use udev.

> I agree using udev is a solution to the final name problem in /dev,
> as long as they are using 2.6, (altough I have to support 2.4 as well).

We aren't talking about 2.4 here though.  2.4 is a totally different
subject.

> But using udev still doesn't allow me to create that custom name in
> /sys/class/tty.

You don't want to do that.  The kernel doesn't want you to do that.
Userspace doesn't want you to do that.  No one wants that.

> I understand this is where you would say we should use the ttyD12143
> value,
> but I feel that it simply doesn't show the "linkage" between that value
> and the "custom" name in /dev as easily as it would if I could create a
> custom name for the tty in /sys/class/tty.

udev will show you that /dev/ttyfoo really is /sys/class/tty/ttyD12143:

	$ udevinfo -n /dev/ttyfoo -q path
	/class/tty/ttyD12143

So you do have that "linkage".  Don't mess around with kernel names,
it's not allowed.  Mess around with userspace names, that's allowed.

thanks,

greg k-h
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