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Date: Fri, 7 Feb 2014 10:02:02 +0100 From: Kay Sievers <kay@...y.org> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: Hannes Reinecke <hare@...e.de>, systemd Mailing List <systemd-devel@...ts.freedesktop.org>, dh.herrmann@...il.com, LKML <linux-kernel@...r.kernel.org>, Lennart Poettering <lennart@...ttering.net>, Jiri Slaby <jslaby@...e.cz>, Werner Fink <werner@...e.de>, Martin Schwidefsky <schwidefsky@...ibm.com> Subject: Re: [PATCHv2] tty: Set correct tty name in 'active' sysfs attribute On Thu, Feb 6, 2014 at 5:29 PM, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote: > On Thu, Feb 06, 2014 at 04:44:20PM +0100, Hannes Reinecke wrote: >> 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 >> >> /dev/3270/tty1 >> >> but the console driver announces the name 'tty3270'. >> So as per current rules the 'active' attribute contains >> >> tty32700 >> >> 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 >> behavior. > > Ok, care to send an updated version, that fixes the Documentation as > well? If Kay agrees that this is the correct solution, I'll be glad to > take it. Sounds good to me. The intention clearly was to point to the device in use, which we can find then. I would not expect problems with this change. For common uses it is the same name already and nothing visibly should change, and for the ones where it isn't the same, I expect it is not too useful to find the driver name. Thanks, Kay -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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