linux-kernel - Re: utrace vs. ptrace

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Message-ID: <44C6B555.7000300@mbligh.org>
Date:	Tue, 25 Jul 2006 17:20:37 -0700
From:	Martin Bligh <mbligh@...igh.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linus Torvalds <torvalds@...l.org>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Albert Cahalan <acahalan@...il.com>, arjan@...radead.org,
	akpm@...l.org, linux-kernel@...r.kernel.org,
	Roland McGrath <roland@...hat.com>
Subject: Re: utrace vs. ptrace

Alan Cox wrote:
> On Iau, 2006-07-13 at 12:05 -0700, Linus Torvalds wrote:
> 
>>Doing core-dumping in user space would be insane. It doesn't give _any_ 
>>advantages, only disadvantages.
> 
> 
> It has a number of very real advantages in certain circumstances and the
> only interface the kernel needs to provide is the debugger interface and
> something to "kick" the debugger and reparent to it, or for that matter
> it might even be viable just to pass the helper the fd of an anonymous
> file holding the dump.
> 
> Taking out the kernel core dump support would be insane.
> 
> We get customers who like to collect/process/do clever stuff with core
> dumps and failure cases. We also get people who want to dump a core that
> excludes the 14GB shared mmap of the database file as another example
> where it helps.

The in-kernel core dumper also seems to hold locks that wedge access
to /proc for that pid, which causes anything walking /proc to wedge.
For large core dumps, that takes far too long, and causes us real
problems

M.
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