Re: [lttng-dev] [barectf] How to ensure that last events before a crash get recorded

[Philippe Proulx via lttng-dev <lttng-dev@lists.lttng.org>]

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On Thu, Mar 4, 2021 at 10:28 RADERMACHER Ansgar via lttng-dev <
lttng-dev@lists.lttng.org> wrote:

> Hi,
>
> when doing tracing with barectf, the trace elements are written into a
> buffer first and only written when the buffer is full - or if the function
> barectf_platform_fs_fini gets called.
> In case of a crash, it's therefore possible to loose some events. What is
> the best option to prevent this issue? I've used signal handlers that call
> the function barectf_platform_fs_fini. This seems to work well with Linux,
> but is not portable. When using the provided sample platform, there is also
> the option to reduce the buffer size, but this is not ideal, as trace
> events that are too big for the buffer are not written.
>

First question: why are you using barectf on Linux vs LTTng?

LTTng supports writing the sub-buffers to NVRAM and, if the system crashes,
convert those sub-buffers to a CTF trace with the lttng-crash utility. See <
https://lttng.org/docs/v2.12/#doc-persistent-memory-file-systems>.

With NVRAM, you could do this with barectf with a corresponding platform
using it. It's always up to the platform author to decide where buffers are
and where complete packets go; it's not a feature of barectf as such.

Hope it helps,

Phil


> Best regards
>
> Ansgar
>
>
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>
-- 
Philippe Proulx

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