>Has anyone successfully used a bpf in nonblock mode?  The manpage 
>states that an ioctl BIOCIMMEDIATE is necessary to switch from
>block (default behaviour) to nonblock.  

BIOCIMMEDIATE doesn't switch from blocking to non-blocking, it
switches the bpf from "return as much data as possible to each read()"
to "return a packet as soon as it arrives".  they both block, but one
returns immediately after the receipt of a packet.

>The ioctl in the code I'm working with seems perform the switch without
>error, however when I go to use the device I get
>
>EAGAIN errno 35  resource temporarily unavailable

that seems to make sense to me.  if there's nothing to read, but you
expect something at some point, it's "temporarily unavailable".

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