Date: Wed, 30 Dec 2015 16:46:39 +0800 From: Julian Elischer <julian@freebsd.org> To: Juan Herrera <mybsdmailing@gmail.com>, freebsd-net@freebsd.org Subject: Re: BPF Berkeley Packet Filter Message-ID: <568399EF.2090409@freebsd.org> In-Reply-To: <CAAN2wCCpbivX6B3xCt4wFCw_6eOQ40nquVJf%2Bz-8RRVyUFa7mA@mail.gmail.com> References: <CAAN2wCCpbivX6B3xCt4wFCw_6eOQ40nquVJf%2Bz-8RRVyUFa7mA@mail.gmail.com>
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On 30/12/2015 12:22 PM, Juan Herrera wrote: > Hello BSD folks, > > I am developing a networking application in C and I have a question > regarding BPF (Berkeley Packet Filters), > I will give you an idea of the app first, I need to send a packet from > machine A to machine B (any kind of packet) so for this I wrote a packet > generator application which will send a packet to machine B, but before > sending the packet I need to append some metadata values at the end of the > packet, already done, so in machine B I have a raw socket listener app > ready to receive incoming packets from machine A, however I want to > implement filtering with BPF on machine B, but as my metadata was appended > at the end of the packet (have to be at the end), I need to read the packet > length with(using) Berkeley Packet Filter to match a specific field to > filter one of the bytes at the end of my packet (metadata appended), in > other words I need to know the incoming packet length to filtered against > one of the metadatas fields and be able to drop the packet before reaching > user space applications(drop it in kernel space). > > So my question is, Can I use BPF to read the packet length to do what I > want? you mean can you use a bpf filter to act upon a trailer? yes you can look at the man page for BPF_LD and BPF_LEN > > Thank you in advance! > > Happy Holidays! > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >
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