[yocto] [ptest-runner] Run ptests via stdbuf configured to line-buffering

[Mikko.Rapeli at bmw.de]

On Thu, Apr 04, 2019 at 10:48:17PM +0100, Richard Purdie wrote:
> On Thu, 2019-04-04 at 18:00 +0200, Alexander Kanavin wrote:
> > As ptest-runner communicates with child processes via pipe2(),
> > the corresponding channels are not attached to a pty. In that
> > situation stdio facilities like printf() or fwrite() are fully
> > buffered. If a ptest would use them, without bothering
> > to fflush() the output, ptest-runner will only receive what
> > was written by the child ptest process after a buffer gets filled.
> > If the unit tests are proceeding slowly, this may mean that
> > ptest-runner will erroneously timeout due to an apparent lack of
> > 'signs of life' from the child process.
> > 
> > stdbuf utility from coreutils adjusts the buffering to a line-
> > buffered
> > one, and so ptest-runner will get the lines as soon as they are
> > written.
> > 
> > Signed-off-by: Alexander Kanavin <alex.kanavin at gmail.com>
> > ---
> >  utils.c | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> I'm a little torn on this. I noticed some of the run-ptest scripts use
> "| sed -u" whilst the one you were seeing problems with uses "| sed"
> without -u.
> 
> We may want to consider strongly recommending -u. I'm testing a patch
> with some tweaks like that in it...

Please no. I'm running images without sed and using busybox sed instead, and that
doesn't support -u. I'd rather be compatible with sed from busybox to keep changes
to images minimal (e.g. install of additional packages) before executing ptests.

-Mikko