BSD socket identifier

rrlangly · 04-09-2011, 06:42 PM

I'm storing a list of 'struct socket' connections inside my kernel module and making associations from the BSD interface to the protocol interface in my kernel module. Is there a unique identifier of any sort about a BSD socket so that I can get that socket out of my linked list for later reuse?

Or maybe I'm thinking about them wrong. It seems that almost every socket call passes in 'struct socket' as an argument, so maybe I don't need to store them. But I do want to know which user-space interface socket points to which protocol endpoint (remote host).

Kind of confusing, still trying to wrap my head around all these layers and connections. Any clarification much appreciated.

Mara · 04-10-2011, 02:43 PM

The struct sockets are connected to their file descriptors. Is it the connection you want to have?

rrlangly · 04-10-2011, 03:53 PM

Yes, the file descriptor would work if I had access to it since it's the only unique thing about a socket that I know.

I create a socket and store it on a linked list in my kernel w/ other data. The proto_ops.connect callback gets called, so I search a list of remote hosts and the sockets to them.

My problem is I don't know how to compare the incoming 'struct socket *sock' with the struct socket's in my linked list, I don't have a file desriptor to check that I can tell. The socket ip and port can be the same on multiple sockets. The only unique thing I know about a socket is the file descriptor, but I can't find a good way to get access to it so I can match the userspace fd with the socket in my list.

Code:

static int my_connect(struct socket *sock, struct sockaddr *uaddr, int addr_len, int flags)
{
    //...

    list_for_each(pos, &my_hosts.list) {
        // how to find socket in my_hosts linked list that is the same
        // as the 'struct socket *sock' passed into this func?
    }
}

rrlangly · 04-30-2011, 07:17 PM

Shameless bump. Still stuck.

Mara · 05-01-2011, 06:48 AM

OK, but what is exactly the problem you have now?

rrlangly · 05-02-2011, 06:01 PM

Code:

My problem is I don't know how to compare the incoming 'struct socket *sock' 
with the struct socket's in my linked list, I don't have a file desriptor to check
that I can tell. The socket ip and port can be the same on multiple sockets. The
only unique thing I know about a socket is the file descriptor, but I can't find a 
good way to get access to it so I can match the userspace fd with the socket in my 
list.

A simpler way to put it would be ... how do I get the file descriptor that matches a 'struct socket'? File descriptors are unique, so I just need to find a way to get the file descriptor for a particular socket. But file descriptors aren't passed beyond the socket systemcall's in socket.c.

(from socket.c syscall to connect)
err = sock->ops->connect(sock, (struct sockaddr *)&address, addrlen, sock->file->f_flags);

My proto_ops funcs won't receive file descriptor from this sock->ops->connect() call.

I can see that sockfd_lookup_light() (as shown in socket of net/socket.c) will get me a socket from a fd, but I basically want to get a fd from a socket.