'Walk the Line' Director James Mangold -- Wife Pulls Long Black Veil Down Over Marriage

James Mangold might wanna bust out some Johnny Cash ... the "Walk the Line" director's marriage just fell into a ring of fire -- his wife has filed for divorce.

Catherine Konrad filed the docs earlier this month in L.A. ... citing irreconcilable differences, and requesting joint legal and physical custody of their children -- 2 boys ages 9 and 6. According to the papers, obtained by TMZ, she's also asking for spousal support.

During James and Catherine's 15-years of marriage he racked up some impressive directing credits -- including 'WtL,' "The Wolverine," and "Girl, Interrupted."

He's also responsible for the Tom Cruise/Cameron Diaz bomb, "Knight and Day" -- but Catherine does NOT hold that against him in her divorce docs.