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

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Message-ID: <BANLkTik2KqKGwBAqN+CSz7_ergx5VM9x4A@mail.gmail.com>
Date:	Tue, 28 Jun 2011 14:30:36 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.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)

On Tue, Jun 28, 2011 at 10:25 AM, Tejun Heo <tj@...nel.org> wrote:
> 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".

This is true for any new addition to API.
It starts from some kernel version.

> 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.

This new feature looks orthogonal to PTRACE_SEIZE to me.

-- 
vda
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