绑定如何在内核空间内部工作？

Question

Can anyone help me in tracing bind() system call in socket programming. I would like to know what happens when bind() is called, in kernel space. Like which are the structures it updates and what functions are invoked in lower level

Answer 1

The bind(2) system call just configures the local side's address parameters that a socket will use once you have connected (or sendto(2) ). If you don't use it, the kernel selects defaults for it, depending on the underlying protocol.

The exact procedure bind(2) follows depends on the protocol family you are working on, as bind will behave differently depending if you are using PF_UNIX , PF_INET , PF_PACKET , PF_XNS , etc.

For example, in Unix sockets, you'll get your socket associated to an inode in the filesystem (an inode that supports unix sockets, of course), so clients have a path to connect to (in Unix sockets, addresses are paths in the filesystem). In TCP/IP sockets, you can fix the local IP address or the local IP port your socket can listen on (to accept connections) or you can force a IP address and/or port to connect from, to a server.

For a deeper understanding of networking sockets internals, I recommend you reading the excellent book from WR Stevens "TCP/IP Illustrated Vol 2. The implementation," describing the implementation of BSD sockets in NET2. It's old, but still the best explanation ever made. For a good introduction of the BSD socket system calls use, there's also an excellent book (for a long time it was indeed also the best system call reference for BSD unix system calls) by WRStevens: "UNIX network programming, Vol 1 (2ND Ed): The sockets API." Both are two jewels everyone should have available at work.