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    SubjectRe: Why I want PTRACE_O_TRACESTOP option
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    On Fri, 2011-09-09 at 15:01 +0200, Indan Zupancic wrote:
    > On Fri, September 9, 2011 14:26, Indan Zupancic wrote:
    > > Hello,
    > >
    > > On Fri, September 9, 2011 07:54, Denys Vlasenko wrote:
    > >> On Friday 09 September 2011 02:18, Tejun Heo wrote:
    > >>> Hello, Denys.
    > >>>
    > >>> On Thu, Sep 08, 2011 at 06:50:01PM +0200, Denys Vlasenko wrote:
    > >>> > Consider what will happen when a next ptrace fix will require
    > >>> > a way to change ptrace API at runtime. A new option will likely
    > >>> > be introduced, say, PTRACE_O_TRACEPONY, with next available
    > >>> > bit position 7, and perhaps some new event will be generated,
    > >>> > PTRACE_EVENT_PONY, with value.... yes, it can't be 7,
    > >>> > PTRACE_EVENT_STOP took it. So it will probably be 8.
    > >>>
    > >>> Then, just give it the next matching number.
    > >>
    > >> My point is that previously, ptrace behavior was modified by setting
    > >> options. Why don't we use this mechanism? Why we invent a different
    > >> wheel? Ptrace is ugly as-is, why complicate it even further?
    > >>
    > >> The argument was that SETOPTIONS wasn't suitable for modifying
    > >> attach behavior, but this is fixed by "set options on SEIZE"
    > >> patch. I don't see why we can't use options mechanist to affect
    > >> group-stop behavior now.
    > >
    > > I totally agree with Denys here.
    > >
    > > It is very useful to set options atomically at SEIZE time. Having
    > > SEIZE set some hidden option implicitly only makes things more
    > > confusing and harder to explain what SEIZE does. Please apply Denys'
    > > SEIZE API improvements.
    > >
    > > Another important reason to make PTRACE_O_TRACESTOP an option is
    > > because not everyone uses SEIZE: Users using PTRACE_TRACEME can't
    > > set this option at all. For those PTRACE_O_TRACESTOP is needed.
    > > Using PTRACE_TRACEME is the common case for both strace and gdb.
    >
    > PTRACE_O_TRACESTOP only makes sense if it also affects auto-attach
    > SIGSTOPS, of course. I don't know if it does. It probably should.

    With the patch, it will affect them if it is used in list of options
    passed on SEIZE.

    --
    vda




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