Hi, Another problem I popped into while figuring out how to set the outgoing source address for UDP frames.
In Linux 2.2 UDP sending with specified source address worked on a frame by frame basis, and I would like to keep this behaviour. An aux message would be used in sendmsg() to specify the outgoing source address of a packet. My problem is that it is quite difficult to change the source ip of the skb based on an aux message. In the kernel it works as follows: 1) udp_sendmsg is called 2) which in turn calls ip_cmsg_send, which sets up an ipcm_cookie struct 3) this struct is then passed to ip_build_xmit(), which sets up the skb based on ipcm My problem is that to attach create a new cmsg, I'd need to modify the cmsg_cookie struct as it is the only connection between the skb and sendmsg(), and in addition ip_build_xmit() must also be changed as this is the one which processes messages. An alternative way would be add a translation entry about the required change to the TPROXY translation table. The problem with this that adding the entry, sending a single frame, and removing the entry doesn't seem to be very atomic to me. (the only possibility here would be to create a flag assigned to the translation entry, saying that this entry is applied only once => but this might cause problems on SMP, as two processes might be issuing sendmsg() calls at the same time) Opinions? -- Bazsi PGP info: KeyID 9AF8D0A9 Fingerprint CD27 CFB0 802C 0944 9CFD 804E C82C 8EB1
