sync_merge
int sync_merge(const char *name, int fd1, int fd2);
d = sync_merge("mergeFence", b, a);
d = sync_merge("mergeFence", c, d);
merged = sync_merge("mergeFence", fence, fence);
merged = sync_merge("name", tmp, fence);
merged = sync_merge("merge", tmpfence, fence);
merged = sync_merge("mergeFence", fenceB, fenceA);
merged = sync_merge("mergeFence", fenceC, merged);