This is an image of the 12th century Irish Kingship ceremony. Note the pants, the linen tunics and the ionars. In particular, notice the guy just to the left of the tub, how his leine is not visible under the ionar, and the ionar only goes to his elbows and has a hood.
This photo is of Master Leith, who pretty much nails what I think I’m looking at. Although maybe with the occasional trews. I took it with his permission at the An Tir Bardic and A&S Championship in Stromgard, March 2014. I especially liked his ionar’s sleeve length because the story I performed had a description of Laeg’s jacket as having a cowl (not on this leine) but with sleeves “open at the elbows.” (Laeg is Cuchullain’s charioteer)
Katrine brought these to the party (more primary sources).