USER_MEM
if (posix_memalign(&__user_addr_min, PAGE_SIZE, USER_MEM) != 0)
__user_addr_max = __user_addr_min + USER_MEM;
__user_addr_max - USER_MEM/4, USER_MEM/4);
for (i = 0; i < USER_MEM/4; i++)
((char *)__user_addr_max - USER_MEM/4)[i] = i;
assert(riov.used == RINGSIZE * USER_MEM/4);
for (i = 0; i < RINGSIZE * USER_MEM/4; i += 3) {
if (err != 3 && i + err != RINGSIZE * USER_MEM/4)
char *data = __user_addr_max - USER_MEM/4;
struct vring_desc *d = __user_addr_max - USER_MEM/2;