linux-kernel - Re: [PATCH 2.6.25-4] getdelays.c: signal handling for log rotation

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Date:	Sat, 07 Jun 2008 03:13:01 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Scott Wiersdorf <scott@...ehost.com>
CC:	Balbir Singh <balbir@...ibm.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, matt@...ehost.com
Subject: Re: [PATCH 2.6.25-4] getdelays.c: signal handling for log rotation

Scott Wiersdorf wrote:
> On Fri, Jun 06, 2008 at 03:59:09PM +0200, Andi Kleen wrote:
>> Scott Wiersdorf <scott@...lcode.org> writes:
>>
>>> This adds a USR1 signal handler to getdelays.c, which causes getdelays
>>> to close its logfile and reopen it (if '-w logfile' is
>>> specified). This is useful in situations when getdelays is running for
>>> a long time (i.e, the log file growing) and you need to rotate the
>>> logs but don't want to lose any log data.
>> You could do the same by sending SIGSTOP; copy file; truncate file; SIGCONT
> 
> Actually, I was wrong in my previous reply. Sorry for my error. The
> above will work fine (no data loss; I guess the data queues somewhere
> in some magic way?)

netlink has a socket buffer like all other buffer. I think it's around
128K.

> I still think a single handler is elegant enough though, and works
> better with many log rotation systems that want to send a single
> signal to a pid (it's what we need where I'm working now, hence the
> patch).

Well in general it would be cool if there was nicer free userland for
the obscure but useful delay accounting. The code in Documentation
is really not much more than a example. Do you have something downloadable?

-Andi

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