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

[Alexander Kanavin <alex.kanavin@gmail.com>]

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(-)

diff --git a/utils.c b/utils.c
index 504df0b..1376e39 100644
--- a/utils.c
+++ b/utils.c
@@ -243,16 +243,13 @@ filter_ptests(struct ptest_list *head, char **ptests, int ptest_num)
 static inline void
 run_child(char *run_ptest, int fd_stdout, int fd_stderr)
 {
-	char **argv = malloc(sizeof(char) * 2);
+	char* argv[] = {"stdbuf", "-oL", "-eL", "./run-ptest", NULL};
 	chdir(dirname(strdup(run_ptest)));
 
-	argv[0] = run_ptest;
-	argv[1] = NULL;
-
 	dup2(fd_stdout, STDOUT_FILENO);
 	// XXX: Redirect stderr to stdout to avoid buffer ordering problems.
 	dup2(fd_stdout, STDERR_FILENO);
-	execv(run_ptest, argv);
+	execvp(argv[0], argv);
 
 	exit(1);
 }
-- 
2.17.1