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

Mikko Rapeli

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-
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 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.


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