Jtag uart output to a file?

One obvious solution is to launch the nios2-terminal and redirect it's standard output to a file.

I do wonder what you'll be gaining with a filesystem as far as efficiency. It sounds like you'll still be using printf statements so you'll suffer the overhead of that function regardless. You'll still be using the jtag uart to pass the data to the PC which is inherently slow.

You can always use Altera host-based filesystem which creates a filesystem accessible to the NIOS via JTAG if that's what you're looking for. See page 6-15 of the following:

http://www.altera.com/literature/hb/nios2/n2sw_nii5v2_02.pdf

Jake