ref: 02ac617541ca1a7bf82b1615fb5a58235469b5d3
dir: /lib9/readn.c/
#include "lib9.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; }