  We characterize positive links in terms of strong quasipositivity,
homogeneity and the value of Rasmussen, Beliakova and Wehrli's $s$-invariant.
We also study almost positive links, in particular, determine the
$s$-invariants of almost positive links. This result suggests that all almost
positive links might be strongly quasipositive. On the other hand, it implies
that almost positive links are never homogeneous links.
