[lttng-dev] [PATCH RFC lttng-tools] Testpoint mechanism

[Brosseau, Yannick]

I'm not sure I understand the goal of this feature. Can you explain more?
On Sep 11, 2012 4:56 PM, "Christian Babeux" <christian.babeux at efficios.com>
wrote:

> Hi,
>
> This is a RFC for a testpoint mechanism to ease and improve testing
> efforts of the LTTng codebase.
>
> Motivation
> ----------
>
> The main goal behind the testpoint mechanism is to be able to test and
> validate failure cases in different portion of the LTTng codebase. It
> could also be used by developers as a debugging aid.
>
> By injecting code at runtime in the lttng daemons/processes/executables,
> we can painlessly trigger faulty behavior, test errors paths or even
> reproduce race conditions by introducing or exacerbating delays between
> threads.
>
> Requirements
> ------------
>
> The testpoint mechanism should be able to be triggered via scripts to
> automate testing efforts.
>
> Ideally, the testpoint mechanism should *NOT* incur a significant
> performance hit if we want to leave it always on, in a similar fashion
> to the assert() macros.
>
> By leaving it always on, any user is able to use our tests and validate
> the behavior of his installation via a simple 'make check' execution.
>
> Proposed solution
> -----------------
>
> This patch introduce two new macros: TESTPOINT_DECL(name)
> and testpoint(name).
>
> Here a quick example that shows how to use the testpoint mechanism:
>
> file: main.c
> #include <stdio.h>
> #include <common/testpoint/testpoint/testpoint.h>
>
> /* Testpoint declaration */
> TESTPOINT_DECL(interesting_function)
>
> void interesting_function(void)
> {
>         testpoint(interesting_function);
>         /* Some processing that can fail */
>         ...
> }
>
> int main(int argc, char *argv[])
> {
>         interesting_function();
>         ...
>         printf("End");
> }
>
> file: testpoint.c
> #include <stdio.h>
> void __testpoint_interesting_function(void)
> {
>         printf("In testpoint of interesting function!");
> }
>
> Compile:
> gcc -o test main.c
> gcc -fPIC -shared -o testpoint.so testpoint.c
>
> Run:
> > ./test
>   End
> > export LTTNG_TESTPOINT_ENABLE=1
> > LD_PRELOAD=testpoint.so ./test
>   In testpoint of interesting function!
>   End
> > export LTTNG_TESTPOINT_ENABLE=0
> > LD_PRELOAD=testpoint.so ./test
>   End
>
> The testpoint mechanism is triggered via the preloading of a shared
> object containing the appropriate testpoint symbols and by setting the
> LTTNG_TESTPOINT_ENABLE environment variable.
>
> The check on this environment variable is done on the application startup
> with the help of a constructor (lttng_testpoint_check) which toggle a
> global
> state variable indicating whether or not the testpoints should be
> activated.
>
> When enabled, the testpoint() macro calls an underlying wrapper specific to
> the testpoint and simply try to lookup the testpoint symbol via a dlsym()
> call.
>
> When disabled, the testpoint() call will only incur an additionnal test
> per testpoint on a global variable. This performance 'hit' should be
> acceptable for production use.
>
> As stated previously, the testpoint mechanism should be *always on*.
> It can be explicitly disabled via CFLAGS="-DNTESTPOINT" in a way similar
> to NDEBUG and assert().
>
> Comments, thoughts?
>
> Thanks,
>
> Christian Babeux (1):
>   New testpoint mechanism to instrument LTTng binaries for testing
>     purpose
>
>  configure.ac                     |  1 +
>  src/common/Makefile.am           |  2 +-
>  src/common/testpoint/Makefile.am |  6 +++
>  src/common/testpoint/testpoint.c | 43 +++++++++++++++++++++
>  src/common/testpoint/testpoint.h | 81
> ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 132 insertions(+), 1 deletion(-)
>  create mode 100644 src/common/testpoint/Makefile.am
>  create mode 100644 src/common/testpoint/testpoint.c
>  create mode 100644 src/common/testpoint/testpoint.h
>
> --
> 1.7.11.4
>
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lttng.org/pipermail/lttng-dev/attachments/20120911/adf1c39e/attachment.html>