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msocket.md

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Using several networking stack together: msocket

what

A new system call:

int msocket(char * path, int domain, int type, int protocol);

It is like socket(2): the new argument path identifies the stack to use.

why

Because there can be several networking stacks available for a process.

Because while UNIX uses the file system as a global naming facility (e.g. devices, PF_LOCAL sockets, etc), networking support does not use it yet.

how

We propose a new filetype S_IFSTACK for networking stack special files.

Programmers can choose among the available stacks using msocket instead of socket(2).

e.g.: This statement opens a TCP socket using the stack /dev/net/mynet

fd = msocket("/dev/net/mynet", AF_INET, SOCK_STREAM, 0);

It is possible to define a default stack for each address family. In a system providing msocket, the default stack is used for socket(2) or when in msocket the argument path is NULL,

The definition of the default stack is a feature of msocket: when the argument type is SOCK_DEFAULT msocket does not define any communication endpoint, instead it defines the stack that will be used for the successive
msocket calls with NULL path, or for the successive (obsolete) socket(2) calls.

e.g.: The following excerpt of a C program defines the default stack for IPV4 to be /dev/net/topnet and then it opens a TCP socket (that will be provided by the current default stack, i.e.`topnet):

if (msocket("/dev/net/topnet", AF_INET, SOCK_DEFAULT, 0) < 0)
	/* error handling */;
fd = socket(AF_INET, SOCK_STREAM, 0);

This feature provides backwards compatibility for programs using socket(2) in environments where there are several available stacks. These programs will be able to use one stack at a time. Several instances of the same program can use different stacks.

where

msocket is implemented in vuos. Vuos, in fact, permits to extend the set of system calls available to processes.

The utility command vustack (also in vuos) allows users to choose the current default stack.

references:

Renzo Davoli and Michael Goldweber. msocket: multiple stack support for the berkeley socket API. In Proc. of ACM SAC '12. 2012, pp. 588-593.