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From: Guy Harris <guy@alum.mit.edu>
Date: Mon, 8 Sep 2003 16:18:37 -0700
To: Dmitry Morozovsky <marck@rinet.ru>
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cc: hackers@freebsd.org
Subject: Re: if bpf fd's select()able?
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> However, my tests show that select()ing bpf fd does not lead to 
> trigger packets
> available to bpf filter; the process hangs in select state while 
> parallel
> tcpdump process shows packets desired *and* is in bpf state.

See PR kern/22063 "bpf when used with the select system call with 
timeout doesn't forward packets on timeout".

That *should* work in 4-STABLE, as that fix is in 4-STABLE.  You should 
not have to turn BIOCIMMEDIATE on (tcpdump doesn't).