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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 09:59:38 +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,
        bdonlan@gmail.com, pedro@codesourcery.com
References: <1308043218-23619-1-git-send-email-tj@kernel.org> <1308043218-23619-3-git-send-email-tj@kernel.org> <201106180955.37531.vda.linux@googlemail.com>
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On Saturday 18 June 2011 09:55, Denys Vlasenko wrote:
> On Tuesday 14 June 2011 11:20, Tejun Heo wrote:
>    #define PTRACE_EVENT_FORK    1
>    #define PTRACE_EVENT_VFORK   2
>    #define PTRACE_EVENT_CLONE   3
> >  #define PTRACE_EVENT_EXEC	4
> >  #define PTRACE_EVENT_VFORK_DONE	5
> >  #define PTRACE_EVENT_EXIT	6
> > +#define PTRACE_EVENT_STOP	7
> 
> Er... these constants were corresponding exactly to
> bit positions in ptrace options which enable them:
> 
> #define PTRACE_O_TRACESYSGOOD   0x00000001
> #define PTRACE_O_TRACEFORK      0x00000002
> #define PTRACE_O_TRACEVFORK     0x00000004
> #define PTRACE_O_TRACECLONE     0x00000008
> #define PTRACE_O_TRACEEXEC      0x00000010
> #define PTRACE_O_TRACEVFORKDONE 0x00000020
> #define PTRACE_O_TRACEEXIT      0x00000040
> 
> For example, PTRACE_O_TRACEEXEC is 4th bit, PTRACE_EVENT_EXEC is 4.
> 
> If we'd define PTRACE_EVENT_STOP as 7, any future added
> PTRACE_O_foo bit with value 0x00000080 will be unable
> to follow this convention.
> 
> I propose to define PTRACE_EVENT_STOP as 64 instead, leaving 64 low
> PTRACE_EVENT_foo constants for possible future PTRACE_O_foo bits.
> 
> [32 should be enough too, but I feel paranoid today :)]

...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.

Then, PTRACE_EVENT_STOP indeed should be 7.

-- 
vda

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