ref: 8a53b8192db4848626722a00bf4478a2836102d8
dir: /sys/src/cmd/unix/u9fs/readn.c/
#include <plan9.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; }