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

[<Mikko.Rapeli@bmw.de>]

On Fri, Apr 05, 2019 at 07:46:00AM +0100, richard.purdie@linuxfoundation.org wrote:
> On Fri, 2019-04-05 at 06:16 +0000, Mikko.Rapeli@bmw.de wrote:
> > 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@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.
> 
> The other alternative option being proposed is for ptest-runner to
> depend on coreutils which is worse?

GNU sed does not come from coreutils but from sed recipe.

Your call in the end. I just provided my point of view.

> I did test the -u option to sed in the openssh ptest runner and it did
> fix the problems we've been seeing.
> 
> I'm open to other alternatives but the -u option to sed is looking like
> the best one we have right now. These bugs are making our testing of
> ptests effectively useless and unpredictable so this is a serious
> issue...

Understood. I hope you could also add 'set -eux' to all ptest shell scripts.
Many of them seem to be missing shell script error handling and failures
like providing -u to busybox sed may go unnoticed.

-Mikko