Use modinfo(1M) to confirm that the driver is loaded.
$ modinfo Id Loadaddr Size Info Rev Module Name 6 101b6000 732 - 1 obpsym (OBP symbol callbacks) 7 101b65bd 1acd0 226 1 rpcmod (RPC syscall) 7 101b65bd 1acd0 226 1 rpcmod (32-bit RPC syscall) 7 101b65bd 1acd0 1 1 rpcmod (rpc interface str mod) 8 101ce8dd 74600 0 1 ip (IP STREAMS module) 8 101ce8dd 74600 3 1 ip (IP STREAMS device) ... $ modinfo | grep mydriver 169 781a8d78 13fb 0 1 mydriver (Test Driver 1.5)
The number in the info field is the major number that has been chosen for the driver. The modunload(1M) command can be used to unload a module if the module ID is provided. The module ID is found in the left column of modinfo output.
Sometimes a driver does not unload as expected after a modunload is issued, because the driver is determined to be busy. This situation occurs when the driver fails detach(9E), either because the driver really is busy, or because the detach entry point is implemented incorrectly.