ref: 06ad4e5fff870dc6e7da253c1b15aa715ff2dfb3
dir: /sys/src/ape/lib/ap/plan9/9readn.c/
#include "sys9.h" long _READN(int f, void *av, long n) { char *a; long m, t; a = av; t = 0; while(t < n){ m = _READ(f, a+t, n-t); if(m <= 0){ if(t == 0) return m; break; } t += m; } return t; }