[Testers wanted] /dev/console cleanups

[Jeremy Chadwick]

On Wed, Nov 19, 2008 at 11:48:36PM -0800, Nate Eldredge wrote:
> On Wed, 19 Nov 2008, Jeremy Chadwick wrote:
>
>> On Thu, Nov 20, 2008 at 05:39:36PM +1100, Peter Jeremy wrote:
>
>>> I hope that never gets committed - it will make debugging kernel
>>> problems much harder.  There is already a kern.msgbuf_clear sysctl and
>>> maybe people who are concerned about msgbuf leakage need to learn to
>>> use it.
>>
>> And this sysctl is only usable *after* the kernel loads, which means
>> you lose all of the messages shown from the time the kernel loads to
>> the time the sysctl is set (e.g. hardware detected/configured).  This is
>> even less acceptable, IMHO.
>
> But surely you can arrange that the contents are written out to  
> /var/log/messages first?
>
> E.g. a sequence like
>
> - mount /var
> - write buffer contents via syslogd
> - clear buffer via sysctl
> - allow user logins

This has two problems, but I'm probably missing something:

1) See my original post, re: users of our systems use "dmesg" to find
out what the status of the system is.  By "status" I don't mean "from
the point the kernel finished to now", I literally mean they *expect*
to see the kernel device messages and all that jazz.  No, I'm not
making this up, nor am I arguing just to hear myself talk (despite
popular belief).  I can bring these users into the discussion if people
feel it would be useful.

2) I don't understand how this would work (meaning, technically and
literally: I do not understand).  How do messages like "CPU: Intel(R)
Core(TM)2 Duo CPU E8400 @ 3.00GHz (2992.52-MHz K8-class CPU)" get
written to syslog when syslogd isn't even running (or any filesystems)
mounted at that time?  There must be some magic involved there (since
syslog == libc, not syscall) when syslogd starts, but I don't know
how it works.

> This way the buffer is cleared before any unprivileged users get to do  
> anything.  No kernel changes needed, just a little tweaking of the init  
> scripts at most.
>
> If you should have a crash and suspect there is useful data in the 
> buffer, you can boot to single-user mode (avoiding the clear) and 
> retrieve it manually.
>
> Seems like this should make everyone happy.

What I'm not understanding is the resistance towards Rink's patch,
assuming the tunable defaults to disabled/off.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |