linux-kernel - Re: consolechars switches tty since 8b92e87 vt: add an event interface

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Message-ID: <40e92d5b0911151121l68ef89e5s315b6c2b017bfaad@mail.gmail.com>
Date:	Sun, 15 Nov 2009 20:21:25 +0100
From:	Przemysław Pawełczyk 
	<przemyslaw@...elczyk.it>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: consolechars switches tty since 8b92e87 vt: add an event 
	interface

2009/11/15 Alan Cox <alan@...rguk.ukuu.org.uk>:
>> The problem is that since 8b92e87 running consolechars switches tty to
>> the one provided with --tty option. Last commit I have tested,
>> a9366e6, is still affected.
>
> That is a suprise as the code shouldn't be changing the behaviour of any
> application unless something happened to rely on the race it fixed. Even
> then I wouldn't expect what you see.
>
> What does an strace of that command look like so I can see what ioctls it
> issues and in what order.

# strace /usr/bin/consolechars --tty=/dev/tty2 -f lat0-sun16
[ snip ]
open("/dev/tty2", O_RDWR)               = 3
ioctl(3, KDGKBTYPE, 0x7fff042a0177)     = 0
[ snip ]
ioctl(3, KDFONTOP, 0x7fff042a0150)      = 0
[ snip ]
fstat(3, {st_mode=S_IFCHR|0600, st_rdev=makedev(4, 2), ...}) = 0
ioctl(3, VT_GETSTATE, 0x7fff042a0130)   = 0
ioctl(3, VIDIOC_G_COMP or VT_ACTIVATE, 0x2) = 0
ioctl(3, VIDIOC_S_COMP or VT_WAITACTIVE, 0x2) = 0
ioctl(3, PIO_UNIMAPCLR, 0x7fff042a0160) = 0
ioctl(3, PIO_UNIMAP, 0x7fff042a0730)    = 0
ioctl(3, VIDIOC_G_COMP or VT_ACTIVATE, 0x1) = 0
ioctl(3, VIDIOC_S_COMP or VT_WAITACTIVE, 0x1) = 0
exit_group(0)

And by switching tty I mean what is meant by switching tty manually,
i.e. the result of pressing Alt+Fx under x86. Just to clarify.

I have one thing to add. It looks like that is not fully deterministic
behavior, at least not at f278a2f^ I'm using now. Occasionally tty
isn't switched. I wasn't aware of this before.

I just booted that f278a2f^ (i.e. 569ec4c) while consolechars were
limited only to console-setup script, but this time tty1 remained on
the screen and I didn't get "INIT: open(/dev/console): Input/output
error" I was seeing before. I'm not sure whether it is relevant here.

> Alan

-- 
Przemysław Pawełczyk
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