in pathconf, -1, not 0, means unsupported.. syncio presumably works, too.
[musl] / src / fcntl /
drwxr-xr-x   ..
-rw-r--r-- 158 creat.c
-rw-r--r-- 381 fcntl.c
-rw-r--r-- 319 open.c
-rw-r--r-- 337 openat.c
-rw-r--r-- 192 posix_fadvise.c
-rw-r--r-- 176 posix_fallocate.c