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

Mikko Rapeli

On Fri, Apr 05, 2019 at 07:46:00AM +0100, wrote:
On Fri, 2019-04-05 at 06:16 +0000, 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
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-
one, and so ptest-runner will get the lines as soon as they are

Signed-off-by: Alexander Kanavin <>
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
"| sed -u" whilst the one you were seeing problems with uses "|
without -u.

We may want to consider strongly recommending -u. I'm testing a
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
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.


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