Re: [PATCH -tip 3/3] Add get_signal tracepoint

[Masami Hiramatsu <mhiramat@redhat.com>]

Roland McGrath wrote:
>> Hmm, actually, trace_signal_send() doesn't record the return value.
>
> Is that because it's called before the action really happens?
> Is it important that it be called beforehand?  If it's called
> afterwards, it's easy to pass the return value.

I'm not so sure why signal sending events was put beforehand.
However, I assume that original intent might be recording
the *timing* of all signal generation (including SIGSTOP/CONT).

>> So, what about trace_signal_overflow() for RT-signals and
>> trace_signal_loss_info() for non-RT?
>
> Really you can distinguish those just by looking at sig and info, so
> perhaps a single tracepoint is enough.

Ah, right :-)

>  I guess it really depends on what
> filtering you would want and how inconvenient it is to have to apply that
> filtering.  Having these two distinct tracepoints lets you trivially trace
> only "silent information loss" without seeing the events where userland
> gets full information (if applications are paying attention).
>
> If you want to have a full suite of tracepoints where each one covers one
> unambiguous corner of the semantics, then there are more than these just
> for sending.  e.g. see below.

As Ingo said, I think this kind of finegrained events are optional.
I don't think we really need these events soon. IMHO, just adding
signal-loss event is enough at the first step.

But anyway, thank you so much for suggesting those tracepoints!

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com