linux-kernel - Re: How do I choose an arbitrary minor number for my tty device?

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Message-ID: <20101118171856.GA4283@suse.de>
Date:	Thu, 18 Nov 2010 09:18:56 -0800
From:	Greg KH <gregkh@...e.de>
To:	Timur Tabi <timur@...escale.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Scott Wood <scottwood@...escale.com>,
	Stuart Yoder <stuart.yoder@...escale.com>
Subject: Re: How do I choose an arbitrary minor number for my tty device?

On Thu, Nov 18, 2010 at 10:56:43AM -0600, Timur Tabi wrote:
> Greg KH wrote:
> > Why?  Again, it doesn't matter, and no other tty driver does it.
> > 
> > Actually you do have control over it, if you really want it, but again,
> > don't do that :)
> 
> Because the only way to know which byte channel tty you want is via the byte
> channel handle.
> 
> Think of the situation where you have two serial ports on the back of your
> computer.  One of them is /dev/ttyS0, and the other is /dev/ttyS1.  But which
> one is which?  The only way to find out is try one and see if it works.

No, you can use the /dev/serial/ links to determine exactly which is
which depending on the pci id, and other unique identifiers (serial
numbers, etc.)

> Now that might be acceptable for serial ports that are fixed physically.  But
> byte channels handles are completely arbitrary and easily change with even the
> slightest re-configuration of the partitions under the hypervisor.  I need to
> have some way to tell userspace that /dev/ttybc0 is byte channel handle 73.

Then again, just use the /dev/serial/ symlinks that are there for you.

> > Sorry, I can't do code review, or accept code that is not allowed to be
> > sent to the public, as, surprise, I'm public :)
> 
> Well, ok.  I didn't want to spam the mailing list with something that only you
> asked for, but here it is:

Is this somehow not public code?  What just changed in the past 15
minutes?

confused,

greg k-h
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