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Message-ID: <52F24858.4020208@hurleysoftware.com>
Date: Wed, 05 Feb 2014 09:19:04 -0500
From: Peter Hurley <peter@...leysoftware.com>
To: David Herrmann <dh.herrmann@...il.com>
CC: Hannes Reinecke <hare@...e.de>,
systemd Mailing List <systemd-devel@...ts.freedesktop.org>,
Kay Sievers <kay@...y.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.cz>
Subject: Re: [systemd-devel] [PATCH] tty: Set correct tty name in 'active'
sysfs attribute
This patch won't get very far if not addressed to the actual maintainers
[ +cc Greg Kroah-Hartman, Jiri Slaby]
On 02/05/2014 09:05 AM, David Herrmann wrote:
> Hi
>
> On Wed, Feb 5, 2014 at 2:53 PM, Peter Hurley <peter@...leysoftware.com> wrote:
>> On 02/05/2014 07:53 AM, David Herrmann wrote:
>>>
>>> Hi
>>>
>>> On Wed, Feb 5, 2014 at 11:11 AM, Hannes Reinecke <hare@...e.de> wrote:
>>>>
>>>> The 'active' sysfs attribute should refer to the currently
>>>> active tty devices the console is running on, not the currently
>>>> active console.
>>>> The console structure doesn't refer to any device in sysfs,
>>>> only the tty the console is running on has.
>>>> So we need to print out the tty names in 'active', not
>>>> the console names.
>>>>
>>>> Cc: Lennart Poettering <lennart@...ttering.net>
>>>> Cc: Kay Sievers <kay@...y.org>
>>>> Signed-off-by: Werner Fink <werner@...e.de>
>>>> Signed-off-by: Hannes Reinecke <hare@...e.de>
>>>> ---
>>>> drivers/tty/tty_io.c | 14 ++++++++++++--
>>>> 1 file changed, 12 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
>>>> index c74a00a..17db8ca 100644
>>>> --- a/drivers/tty/tty_io.c
>>>> +++ b/drivers/tty/tty_io.c
>>>> @@ -3545,9 +3545,19 @@ static ssize_t show_cons_active(struct device
>>>> *dev,
>>>> if (i >= ARRAY_SIZE(cs))
>>>> break;
>>>> }
>>>> - while (i--)
>>>> + while (i--) {
>>>> + const struct tty_driver *driver;
>>>> + const char *name = cs[i]->name;
>>>> + int index = cs[i]->index;
>>>> +
>>>> + driver = cs[i]->device(cs[i], &index);
>>>> + if (driver) {
>>>> + index += driver->name_base;
>>>> + name = driver->name;
>>>> + }
>>>> count += sprintf(buf + count, "%s%d%c",
>>>> - cs[i]->name, cs[i]->index, i ? '
>>>> ':'\n');
>>>> + name, index, i ? ' ':'\n');
>>>> + }
>>>
>>>
>>> Nice catch and indeed, systemd already relies on these names to be
>>> identical to their char-dev name. Fortunately, VTs and most serial
>>> devices register the console with the same name as the TTY, so we're
>>> fine.
>>
>>
>> What device did this trip over?
>
> I haven't seen one so far, but to me it's a coincident, not something
> we should rely on.
>
>> Also, this file is not private to systemd. Maybe these changes should
>> be forked into a different sysfs attribute, "active_devices"?
>
> What's the use-case to return the name of the console-driver? There is
> no way for user-space to read active console-drivers anywhere so I
> think returning the TTY makes more sense. We already have working
> user-space that can spawn gettys on active consoles via this file. I
> am open to change this to "active_devices" as the existing interface
> was clearly not designed to return the device-names.
>
> However, given the fact that both matched so far, I think changing the
> existing interface to the only user I am aware of is better than
> adding a new interface just to keep this unused attribute. But
> obviously it's the maintainer's/your decision and you might know
> user-space which requires the console-names instead of the tty-names.
> So please let us know which way to go as we would like to see a
> reliable way to match active consoles to TTY devices for automated
> getty-startup.
Sure, I get it. Just wanted to point out the obvious right up front
so that if it turns out there is another userspace dependency and
this gets rewound, possibly across future -stable kernels, the
fallout could get ugly.
Regards,
Peter Hurley
PS - The "active" attribute won't be unused; old systemd's will
still depend on it, yes?
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