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Date:	Thu, 06 Feb 2014 16:44:20 +0100
From:	Hannes Reinecke <>
To:	Greg Kroah-Hartman <>
CC:	systemd Mailing List <>,,,
	Lennart Poettering <>,
	Kay Sievers <>, Jiri Slaby <>,
	Werner Fink <>,
	Martin Schwidefsky <>
Subject: Re: [PATCHv2] tty: Set correct tty name in 'active' sysfs attribute

On 02/06/2014 04:29 PM, Greg Kroah-Hartman wrote:
> On Thu, Feb 06, 2014 at 03:27:43PM +0100, Hannes Reinecke wrote:
>> The 'active' sysfs attribute should refer to the currently
>> active tty devices the console is running on, not the currently
>> active console.
> That's not what Documentation/ABI/sysfs-tty says:
>                  Shows the list of currently configured                         
>                  console devices, like 'tty1 ttyS0'.                            
>                  The last entry in the file is the active                       
>                  device connected to /dev/console.                              
>                  The file supports poll() to detect virtual                     
>                  console switches.                         
The problem is indeed with 'console devices'. There is no such
thing; you only have tty devices where the console is running on.

>> The console structure doesn't refer to any device in sysfs,
>> only the tty the console is running on has.
> That sentance doesn't make sense.
>> So we need to print out the tty names in 'active', not
>> the console names.
> But that doesn't match the documentation.
> What exactly are you trying to "fix" here?  What is the problem that the
> current file has that is broken?  And as you are changing what this file
> means, what will break if the information in the file changes?
systemd is using the 'active' sysfs attribute to figure out on which
_tty_ device to start a getty on.
As soon as the console name and the tty name are different
you have no means of figuring out which _device_ to open.
AFAICS the console 'device' (ie the current entry in 'active')
doesn't have _any_ equivalent in sysfs; it just so happens that for
most console drivers the tty driver name is identical.
But this is not a requirement, and fails for drivers which have a
different device for the console and the tty.

EG on S/390 the 3270 tty has the devices


but the console driver announces the name 'tty3270'.
So as per current rules the 'active' attribute contains


which correct as per documentation, but doesn't have _any_
equivalent in sysfs.

Martin has the grubby details here.

But of course, the documentation should be updated to match the new


Dr. Hannes Reinecke		      zSeries & Storage			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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