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From: Mathieu Desnoyers via lttng-dev <lttng-dev@lists.lttng.org>
To: Norbert Lange <nolange79@gmail.com>
Cc: lttng-dev <lttng-dev@lists.lttng.org>
Subject: Re: [lttng-dev] [PATCH lttng-ust] Improve tracelog handling, reduce exported functions
Date: Thu, 20 May 2021 12:25:35 -0400 (EDT)	[thread overview]
Message-ID: <523808152.52514.1621527935563.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <CADYdroPZTrNg+gYy9SLyDnUGUd1kNq3vkzzjSwJx9e7Tz68quw@mail.gmail.com>

----- On May 20, 2021, at 11:54 AM, Norbert Lange nolange79@gmail.com wrote:
[...]

>> What prevents you from linking against lttng-ust.so again ?
> 
> I did not poke around enough with Lttng to be confident it wont have
> side effects,
> I really don't want it active in production. It doesn't seem there is
> much public knowledge with Xenomai either.
> lttng-ust.so will spawn threads, lttng-ust-tracepoint.so is mostly passive,

There is indeed a split between instrumentation and runtime threads done
with lttng-ust-tracepoint.so vs lttng-ust.so.

I understand that this split is missing for tracelog and tracef, and
would be a good thing to have.

I would be interested to move the tracelog and tracef implementation
from liblttng-ust.so to liblttng-ust-tracepoint.so, even this late
in the -rc cycle, because all users of tracelog/tracef need to link
against liblttng-ust-tracepoint.so anyway. So moving these symbols
should not affect anyone.

Can you give it a try and let me know if it works for you ?

> So Id want a dynamic tracepoint-provider than i can dlopen (so that
> the signal masks are inherited,
> I hope you dont touch them).

The signals are all blocked for lttng-ust listener threads. We don't
modify the signal masks in the tracepoint probes. Not sure which is
the target of your question though.

> 
> Of course I could just remove all lttng libraries on the production
> system aswell. Still doesnt change that
> tracelog and tracef doesnt work that way.

Would moving the tracelog/tracef implementation to liblttng-ust-tracepoint.so
solve your issues ?

> 
> I implemented my own tracelog/tracef using the normal lttng
> tracepoints for now, they totally break on source level with 2.13
> aswell ;)
> is it ok if I do this to access them:
> 
> #define TRACEPOINT_DEFINE
> #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
> // 2.12
> // #include <lttng/lttng-ust-tracelog.h>
> // #include <lttng/lttng-ust-tracef.h>
> // 2.13
> #include <lttng/tp/lttng-ust-tracelog.h>
> #include <lttng/tp/lttng-ust-tracef.h>
> 
> ie. I would load lttng-ust.so later and can then use those tracepoints.

Reimplementing the tracelog/tracef providers is not an intended use-case.
I'd very much prefer if we move their implementation to
liblttng-ust-tracepoint.so.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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  reply	other threads:[~2021-05-20 16:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20 12:18 Norbert Lange via lttng-dev
2021-05-20 12:18 ` [lttng-dev] [PATCH lttng-ust] Improve tracef/tracelog to use the stack for small strings Norbert Lange via lttng-dev
2021-05-20 14:19 ` [lttng-dev] [PATCH lttng-ust] Improve tracelog handling, reduce exported functions Mathieu Desnoyers via lttng-dev
2021-05-20 14:57   ` Norbert Lange via lttng-dev
2021-05-20 15:21     ` Mathieu Desnoyers via lttng-dev
2021-05-20 15:54       ` Norbert Lange via lttng-dev
2021-05-20 16:25         ` Mathieu Desnoyers via lttng-dev [this message]
2021-05-20 16:51           ` Norbert Lange via lttng-dev
2021-05-20 17:18             ` Mathieu Desnoyers via lttng-dev
2021-05-20 17:43               ` Norbert Lange via lttng-dev
2021-05-21 14:55                 ` Mathieu Desnoyers via lttng-dev
2021-05-25 13:32               ` Norbert Lange via lttng-dev

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