linux-kernel - [RFC PATCH 0/1] tracing: support dynamic string field types for synthetic events

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Message-Id: <20200925190806.1870935-1-axelrasmussen@google.com>
Date:   Fri, 25 Sep 2020 12:08:05 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Tom Zanussi <zanussi@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [RFC PATCH 0/1] tracing: support dynamic string field types for
 synthetic events

Hi Steven and Tom,

In this thread: https://lkml.org/lkml/2020/9/17/1015 we discussed how to plumb
dynamic strings into synthetic events. Tom, you proposed adding a new dynamic
string type to synthetic event definition like "char foo[]".

I'm sending this patch because it may be simpler than implementing that (I'm
not too familiar with the tracing infrastructure, apologies if this is not
true), and in my testing it seems sufficient to address my use case. I tested
both setting up a synthetic event as Steven described in the other thread, as
well as doing an analogous thing with a small bpftrace program, and both work as
expected with this patch.

This is because I happen to know there's an upper bound on the length of the
string in question, so I can just define a "char memcg_path[256]" in the
synthetic event, and I can be sure the string won't be truncated.

Let me know what you think. Happy to drop this and wait for Tom's suggested
approach instead.

Axel Rasmussen (1):
  tracing: support dynamic string field types for synthetic events

 kernel/trace/trace_events_hist.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

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2.28.0.681.g6f77f65b4e-goog