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For each supported `PF_*` protocol family (domain), there is a file `/servers/socket/N`
where `N` is the numeric value for the `PF_*` symbol. libc's `socket()`,
`socketpair()` and friends use `_hurd_socket_server` to open them: the latter
computes the `/servers/socket/N` path, then opens it with `__file_name_lookup`,
and returns the result. Since those paths are translated (see showtrans on
`/servers/socket/N`), it's a port to a translator which is returned. Right now
[[`PF_LOCAL`|translator/pflocal]] (a.k.a. `PF_UNIX` or `AF_UNIX`) `N=1`,
[[`PF_INET`|translator/pfinet]] (a.k.a `AF_INET`) `N=2` and
[[`PF_INET6`|translator/pfinet/ipv6]] (a.k.a `AF_INET6`) `N=26` are supported.
In case of problems to find out which server is called rpctrace can be of use:
search for the output `dir_lookup ("servers/socket/N" ...)`
User programs open those files, and use the `socket_create` [[RPC]] to make a
new socket. With that socket, they can use the other `socket_*` RPCs and also
the `io_*` RPCs. The `socket_*` RPCs are essentially clones of the [[Unix]]
[[system call]]s in question.
The only exception is `sockaddrs`, which are implemented as [[ports|libports]]
instead of the opaque data arrays they are in the system calls. You manipulate
`sockaddr` ports with the `socket_create_address`, `socket_fabricate_address`,
and `socket_whatis_address` calls. The `sockaddr` port is then used in socket
calls like `socket_connect` and `socket_accept`.
`PF_INET` `sockaddr` ports are manipulated with `socket_create_address` from
the usual `struct sockaddr_in`. `PF_LOCAL` `sockaddr` ports are stored by
`S_IFSOCK` filesystem nodes; you find the address associated with a node with
`ifsock_getsockaddr`. The [[file_system_server|translator]] will get a
`sockaddr` to return with `socket_fabricate_address`.