in pathconf, -1, not 0, means unsupported.. syncio presumably works, too.
[musl] / src / stdio / setlinebuf.c
1 #define _GNU_SOURCE
2 #include <stdio.h>
3
4 void setlinebuf(FILE *f)
5 {
6         setvbuf(f, 0, _IOLBF, 0);
7 }