null_mount
#define MOUNTTONULLMOUNT(mp) ((struct null_mount *)((mp)->mnt_data))
struct null_mount *nmp;
nmp = kmem_zalloc(sizeof(struct null_mount), KM_SLEEP);
kmem_free(nmp, sizeof(struct null_mount));
kmem_free(nmp, sizeof(struct null_mount));
struct null_mount *nmp = MOUNTTONULLMOUNT(mp);
kmem_free(mp->mnt_data, sizeof(struct null_mount));
const char *null_mount = "/nullm";
RL(rump_sys_mkdir(null_mount, 0777));
RL(rump_sys_mount(MOUNT_NULL, null_mount, 0,
(*pre)(use_layer ? null_mount : mp);
(*post)(use_layer ? null_mount : mp);
RL(rump_sys_unmount(null_mount, 0));