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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 09:55:37 +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
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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 :)]

-- 
vda

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