Date: Tue, 24 Jan 2006 18:23:15 -0800 From: Haisang Wu <haisang@gmail.com> To: freebsd-net@freebsd.org. Subject: Developing New Socket Option on 4.10 Message-ID: <de1c88480601241823l5a382c09i2e296c9f30e95292@mail.gmail.com>
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Hello, all, I am writing for help on my freebsd kernel hacking. I am working on 4.10, and intend to introduct a new socket option (say, SO_TAG_PAK) for my own kernel. When sending out a packet, if this option is set, the socket layer will produce a 20-byte tag, and finally this tag will be prepended before IP header (may be done in ip_output() ). This is somewhat like MPLS's shim layer, but this special packet with the tag will only be sent over a logical tunnel to another system. When receiving a packet, the IP layer will check whether the packet has this tag (through the first integer of the tag), and pass the tag up (to applications). For future possible extensions, I introduced a flag, so_tag_pak_flag, int= o "struct socket". I modified sosetopt() to set so->so_tag_pak_flag=3D0x1 wh= en (sopt->sopt_name =3D=3D SO_TAG_PAK). I will write a function so_tagpak( ) t= o generate the 20-byte tag. This tag will be kept in the kernel space, and later be prepended to the IP packet in function ip_output( ). I have a few questions below: At sending direction: 1. Should I allocate a separate mbuf for this tag inside so_tagpak( )? 2. The function so_tagpak( ) should be called in the socket layer so the socket can check the flag and produce the tag. Where should it be called? 3. In ip_output( ), can I prepend this tag (i.e., a separate mbuf) before the IP header? Could you give me some suggestions on how to do so? At receiving direction: 4. Can I detect the tag in ipintr( )? How will be the mbuf operation here? Thank you very much for your help! Haisang
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