What is the test for challenging the fact or duration of a prisoner's sentence in a civil rights action?

To the extent that a prisoner challenges "the fact or duration of his confinement" the complaint will be construed as a habeas corpus petition, and to the extent the "complaint seeks damages from civil rights violations" the complaint will be construed as a civil rights action. Tucker v. Carlson, 925 F.2d 330, 332 (9th Cir.1991). Where a prisoner challenges the manner in which his sentence was executed, the action is construed as a habeas petition pursuant to 28 U.S.C. Sec. 2241. Id. at 331 (prisoner sought earlier parole by challenging decision not to credit his time in state custody).