NAME

     socket — kernel socket interface

SYNOPSIS

     #include <sys/socket.h>
     #include <sys/socketvar.h>

     int
     sobind(struct socket *so, struct sockaddr *nam, struct thread *td);

     void
     soclose(struct socket *so);

     int
     soconnect(struct socket *so, struct sockaddr *nam, struct thread *td);

     int
     socreate(int dom, struct socket **aso, int type, int proto, struct ucred *cred,
         struct thread *td);

     int
     sogetopt(struct socket *so, struct sockopt *sopt);

     int
     soreceive(struct socket *so, struct sockaddr **psa, struct uio *uio, struct mbuf **mp0,
         struct mbuf **controlp, int *flagsp);

     int
     sosetopt(struct socket *so, struct sockopt *sopt);

     int
     sosend(struct socket *so, struct sockaddr *addr, struct uio *uio, struct mbuf *top,
         struct mbuf *control, int flags, struct thread *td);

     int
     soshutdown(struct socket *so, int how);

DESCRIPTION

     The kernel socket programming interface permits in-kernel consumers to interact with local
     and network socket objects in a manner similar to that permitted using the socket(2) user
     API.  These interfaces are appropriate for use by distributed file systems and other
     network-aware kernel services.  While the user API operates on file descriptors, the kernel
     interfaces operate directly on struct socket pointers.

     Except where otherwise indicated, socket functions may sleep, and are not appropriate for
     use in an ithread(9) context or while holding non-sleepable kernel locks.

   Creating and Destroying Sockets
     A new socket may be created using socreate().  As with socket(2), arguments specify the
     requested domain, type, and protocol via dom, type, and proto.  The socket is returned via
     aso on success.  In addition, the credential used to authorize operations associated with
     the socket will be passed via cred (and will be cached for the lifetime of the socket), and
     the thread performing the operation via td.  Warning: authorization of the socket creation
     operation will be performed using the thread credential for some protocols (such as raw
     sockets).

     Sockets may be closed and freed using soclose(), which has similar semantics to close(2).

   Connections and Addresses
     The sobind() function is equivalent to the bind(2) system call, and binds the socket so to
     the address nam.  The operation would be authorized using the credential on thread td.

     The soconnect() function is equivalent to the connect(2) system call, and initiates a
     connection on the socket so to the address nam.  The operation will be authorized using the
     credential on thread td.  Unlike the user system call, soconnect() returns immediately; the
     caller may msleep(9) on so->so_timeo while holding the socket mutex and waiting for the
     SS_ISCONNECTING flag to clear or so->so_error to become non-zero.  If soconnect() fails, the
     caller must manually clear the SS_ISCONNECTING flag.

     The soshutdown() function is equivalent to the shutdown(2) system call, and causes part or
     all of a connection on a socket to be closed down.

   Socket Options
     The sogetopt() function is equivalent to the getsockopt(2) system call, and retrieves a
     socket option on socket so.  The sosetopt() function is equivalent to the setsockopt(2)
     system call, and sets a socket option on socket so.

     The second argument in both sogetopt() and sosetopt() is the sopt pointer to a struct sopt
     describing the socket option operation.  The caller-allocated structure must be zeroed, and
     then have its fields initialized to specify socket option operation arguments:

     sopt_dir      Set to SOPT_SET or SOPT_GET depending on whether this is a get or set
                   operation.

     sopt_level    Specify the level in the network stack the operation is targeted at; for
                   example, SOL_SOCKET.

     sopt_name     Specify the name of the socket option to set.

     sopt_val      Kernel space pointer to the argument value for the socket option.

     sopt_valsize  Size of the argument value in bytes.

   Socket I/O
     The soreceive() function is equivalent to the recvmsg(2) system call, and attempts to
     receive bytes of data from the socket so, optionally blocking awaiting for data if none is
     ready to read.  Data may be retrieved directly to kernel or user memory via the uio
     argument, or as an mbuf chain returned to the caller via mp0, avoiding a data copy.  The uio
     must always be non-NULL.  If mp0 is non-NULL, only the uio_resid of uio is used.  The caller
     may optionally retrieve a socket address on a protocol with the PR_ADDR capability by
     providing storage via non-NULL psa argument.  The caller may optionally retrieve control
     data mbufs via a non-NULL controlp argument.  Optional flags may be passed to soreceive()
     via a non-NULL flagsp argument, and use the same flag name space as the recvmsg(2) system
     call.

     The sosend() function is equivalent to the sendmsg(2) system call, and attempts to send
     bytes of data via the socket so, optionally blocking if data cannot be immediately sent.
     Data may be sent directly from kernel or user memory via the uio argument, or as an mbuf
     chain via top, avoiding a data copy.  Only one of the uio or top pointers may be non-NULL.
     An optional destination address may be specified via a non-NULL addr argument, which may
     result in an implicit connect if supported by the protocol.  The caller may optionally send
     control data mbufs via a non-NULL control argument.  Flags may be passed to sosend() using
     the flags argument, and use the same flag name space as the sendmsg(2) system call.

     Kernel callers running in ithread(9) context, or with a mutex held, will wish to use non-
     blocking sockets and pass the MSG_DONTWAIT flag in order to prevent these functions from
     sleeping.

SEE ALSO

     bind(2), close(2), connect(2), getsockopt(2), recv(2), send(2), setsockopt(2), shutdown(2),
     socket(2), ng_ksocket(4), ithread(9), msleep(9), ucred(9)

HISTORY

     The socket(2) system call appeared in 4.2BSD.  This manual page was introduced in
     FreeBSD 7.0.

AUTHORS

     This manual page was written by Robert Watson.

BUGS

     The use of explicitly passed credentials, credentials hung from explicitly passed threads,
     the credential on curthread, and the cached credential from socket creation time is
     inconsistent, and may lead to unexpected behaviour.  It is possible that several of the td
     arguments should be cred arguments, or simply not be present at all.

     The caller may need to manually clear SS_ISCONNECTING if soconnect() returns an error.

     The MSG_DONTWAIT flag is not implemented for sosend(), and may not always work with
     soreceive() when zero copy sockets are enabled.

     This manual page does not describe how to register socket upcalls or monitor a socket for
     readability/writability without using blocking I/O.

     The soref() and sorele() functions are not described, and in most cases should not be used,
     due to confusing and potentially incorrect interactions when sorele() is last called after
     soclose().