for GL-XE300 I managed to install snapshot (no documentation there that I need to use uboot, who can update the wiki?).
Then uhttpd was missing.
Then I tried release version.
Mips_24kc, not mipsel_24kc for all ath79 subtargets, I think.
The target dir contains kernel related packages and other packages marked to be built exactly for the target,
Packages dir contains most vanilla packages that can be shared with other similar targets/subtargets.