I just bought a cheap D-Link DWL-G120 “AirPlus” wireless adapter which connects to the PC via USB. I was hoping to either set it in AP (“Master”) mode and use it as an access point (so I can connect to my server from my MacBook wirelessly) or, failing that, in Ad-hoc mode; however, it seems that the prism (p54usb) driver in linux supports neither mode. Not that this is actually documented anywhere or anything, no, that would be too helpful! You can actually set Ad-hoc mode using iwconfig, but then trying to bring up the interface (with “ifconfig wlan0 up”) generates:
SIOCSIFFLAGS: Operation not supported
Needless to say, that’s not very helpful, and there’s no dmesg output which gives any clue as to what the problem is. Your humble narrator spent several hours sifting through kernel source code before he discovered where the problem was (drivers/net/wireless/p54/p54common.c, p54_add_interface() method refuses anything but managed mode; no trivial fix).
I found a patch which apparently adds support for both Master and Ad-hoc modes, and though I managed to apply it against my 188.8.131.52 kernel tree, it doesn’t work and caused a kernel panic when I was messing around with it (so, yeah, not good really). It didn’t apply cleanly so though I assume that there might be some kernel tree out there with working Master mode for the p54, but if there is I can’t find it. The patch doesn’t seem to be applied in the wireless-next tree. Looks like I’ll just have to find a wireless router for the time being.
http://wireless.kernel.org/en/users/Drivers/p54 (yeah, ok, here it says that only Station mode (= Managed mode) works).
Edit 2008-09-01: Hmm. I now have a linksys router running (as an AP) and still can’t connect to it using the D-Link. Can’t be bothered to debug it just now, but I suspect the driver just Does Not Work at all (though it can list various networks it finds on the airwaves, so it works partially at least).