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Re: [PATCH v2 0/4] [RfC] fix tracing for modules

From: Gerd Hoffmann
Subject: Re: [PATCH v2 0/4] [RfC] fix tracing for modules
Date: Thu, 3 Dec 2020 11:39:42 +0100


> I noticed an issue with simpletrace: the trace file does not contain
> qxl_* TRACE_RECORD_TYPE_MAPPING records when ./configure
> --enable-modules is used. This happens because st_write_event_mapping()
> is called before the qxl module calls trace_event_register_group().
> (The mapping records describe the integer ID to string name mapping used
> in a simpletrace file.)

It's not the only initialization issue.  "qemu-system-x86_64 -vga qxl
-trace qxl*" doesn't work either for simliar reasons.

> One way to solve this is by modifying trace_event_register_group() to
> call into trace/simple.c (maybe with a TraceEventIter initialized to
> iterate over the newly registered trace events group?).
> Alternatively, simpletrace.c might be able to emit
> TRACE_RECORD_TYPE_MAPPING on demand instead of ahead of time.

I guess I'll have a look at the first option, or more general at
per-group initialization, that looks like the better approach on
a quick glance.

take care,

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