linux-kernel - Re: [PATCH] ptrace: make former thread ID available via PTRACE_GETEVENTMSG after PTRACE_EVENT

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Date:	Tue, 28 Jun 2011 10:25:12 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ptrace: make former thread ID available via
 PTRACE_GETEVENTMSG after PTRACE_EVENT_EXEC stop (v.2)

Hello,

On Mon, Jun 27, 2011 at 05:18:27PM +0200, Oleg Nesterov wrote:
> > and the only way to discover would be either comparing kernel
> > version or actually trying it - both aren't too nice.
> 
> Fortunately, currently tracehook_report_exec() zeroes ->ptrace_message.
> At least this means that anything != 0 means it works.

Yeah, but that's a pretty silly way to do it.  If we make it depend on
PT_SEIZED, we can simply say "if seized, EXEC reports..." but as it
currently stands, it would go like "If the message is non-zero on
EXEC, it indicates...  This behavior is valid since kernel version
x.x.x".  Maybe adding a guarantee that PTRACE_SEIZE capable kernel
always reports the old pid on EXEC but that would still seem
unnecessarily complicated.  It isn't a bug fix.  I don't see much
point in introducing new behavior separately.

Thanks.

-- 
tejun
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