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From: Denys Vlasenko <vda.linux@googlemail.com>
To: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 2/5] ptrace: implement PTRACE_SEIZE
Date: Sat, 18 Jun 2011 10:57:02 +0200
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Cc: oleg@redhat.com, jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org, indan@nul.nu,
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On Saturday 18 June 2011 10:35, Tejun Heo wrote:
> Hello,
> 
> On Sat, Jun 18, 2011 at 09:59:38AM +0200, Denys Vlasenko wrote:
> > ...unless we plan to introduce PTRACE_O_TRACESTOP (with value 0x00000080)
> > which enables PTRACE_INTERRUPT and stop notifications independently
> > of PTRACE_SEIZE. Which would be very useful for e.g. strace.
> 
> I know you're a big fan of those option flags but I don't really see
> the added value in making these behaviors optional rather than keeping
> things backward compatible - ie. introducing new event needed to be
> gated somehow so the O flags but SEIZE itself serves as a big gate
> anyway so I don't see much point in introducing multiple selectable
> behaviors.  It's not like PTRACE_O_TRACESTOP is gonna make anything
> drastically easier or reduce significant amount of overhead.

I explained this already. strace code is a bit complex, and adding
more complexity so that it uses PTRACE_SEIZE if available, but PTRACE_ATTACH
if it is not, will add some PITA.

Considering that strace does not want PTRACE_SEIZE per se, it only wants
to have a way to properly see and handle group stops, having an option
to enable *only that functonality* without having to use PTRACE_SEIZE
will be useful for strace.

-- 
vda
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