Messages in this thread | | | From | Denys Vlasenko <> | Subject | Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT and group stop notification, take#4 | Date | Fri, 3 Jun 2011 13:37:11 +0200 |
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On Friday 03 June 2011 03:34, Tejun Heo wrote: > > This should alleviate Linus' concerns that we are suffering from unnecessary > > featuritis - that we invent API which is significantly different > > from existing one, and as such users will not use it. > > > > Existing API doesn't use GETSIGINFO data per se to distinguish group-stop from > > signal-delivery-stop, it uses the fact that GETSIGINFO fails on group-stop. > > (Well, arguably it's not a "designed" API, more like "accidentally created API", > > but nevertheless it exists right now). Oleg's proposal means that the new way > > may be makde to work very similarly. > > Okay, you want to preserve %NULL SIGINFO on all STOP traps. Dropping > si_pt_flags and using exit_code makes sense but I think we'll be > better off enabling GETSIGINFO. The affected part of code has to be > changed anyway
Well, not exactly. The affected part of code in strace *has been changed already*. Latest version of strace finally does show "SIGSTOP delivered" and "group-stop happened" events differently.
Now strace, ideally, can have a minimal change
- ptrace(PTRACE_LISTEN, pid, 0, sig); + if (this_is_group_stop) + ptrace(PTRACE_LISTEN, pid, 0, 0); + else + ptrace(PTRACE_SYSCALL, pid, 0, sig);
and boom, group-stops are handled correctly!
> and with %NULL GETSIGINFO we effectively would have > driven ourselves into corner if more information needs to be added > later on.
Oleg thinks that GETSIGINFO may be not the best way to provide additional data. Think about it. It's "get _signal_ info" op. By overloading it to mean something else, we are creating yet another ptrace quirk: "sometimes GETSIGINFO will return something else than signal info".
Oleg says he prefers to add a separate GETfoo op, with cleaner meaning.
> Don't current users unconditionally issue CONT(sig) anyway?
Yes.
-- vda
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