[PATCH] report some ptrace failures; nuke tcp->ptrace_errno

[Denys Vlasenko]

Hi,

I tried to add code which prints a note whenever ptrace fails,
something like "<ptrace(OP):err>".

Looks like "whenever" part of this plan is not easy:
in my testing, I was always striking a case when the resulting
log is messed up in some way...

I would like to commit a limited version of this patch,
which reports only *some* ptrace errors, namely,
errors on ptrace restart operations.

While at it, patch removes tcp->ptrace_errno. I added it many months ago,
and it looks that after all it is not needed for ptrace error detection:
I failed to execute a single existing code path which is accessible
through that variable only.

I used test/sigkill_rain for testing. This patch seems
to generate non-messed-up logs. Basically,
sometimes instead of line like this:

10533 sendto(-1, 0x804895e, 17, 0, NULL, 0 <unfinished ...>

strace will emit line like this:

10533 sendto(-1, 0x804895e, 17, 0, NULL, 0 <ptrace(SYSCALL):No such process>

which tells user that strace failed to let sendto syscall
to be entered - process was dead at that point of time.

I think it is (marginally) better than what we had before.

I observed no other changes in logs while testing.

Please review.
-- 
vda
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