#include <u.h>#include <libc.h> longreadn(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;}