Data communication between L4 (TCP) layer to application layer

Mr.J · 04-06-2009, 11:36 PM

In Linux,TTCP (L4), IP (L3) and L2 (MAC) are implemented in Linux Kernel. When packaet is received at NIC, NIC driver creates sk_buff and fill the data and passed to L3 (based on protocol registered with kernel for L3). and L3 passed sk_buff to L4 (TCP).
Can some body tell me how data from sk_buff from L4 is passed to Application or vice versa (how application delivers data to L4 and ad at what point sk_buff struct is created)

Please help.
James

theNbomr · 04-07-2009, 09:09 AM

The usual way for application code to send and receive TCP/IP data is via the socket() interface.
--- rod.

Mr.J · 04-07-2009, 11:16 PM

That I know... my question is how does it work... I'm looking for data path.

Mara · 04-12-2009, 02:50 PM

It depends slightly on the protocol. When you have a datagram protocol (UDP), socket buffer keeps packets as they were received. The data is copied to user space when requested using read(), readfrom() and such. When an application delivers data to a datagram socket, generally one write equals one packet, so the translation is simple.

The thing with stream-based sockets (TCP) is more complicated. User data may be buffered for some time and that buffer is used to create packets. The other way is similar.