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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.  Only one of
     the uio or mp0 pointers may be non-NULL.  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().