a353a594e0
Add some mention of the functions used by protocol implementations, upcalls, and other general routines. Not all functionality is documented; in particular: o the *at() variants, which are useful only for implementing the corresponding syscalls. o soconnect2(), also only used to implement a syscall (socketpair()). o sockargs(), which is essentually unused and only tangentially socket-related. o selsocket(), which is commented as being present solely for use by netncp and netsmb. o getsockaddr(), which is just a convenience shortcut for copyin(). Reviewed by: jhb (previous version) Approved by: hrs (mentor)
637 lines
16 KiB
Groff
637 lines
16 KiB
Groff
.\"-
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.\" Copyright (c) 2006 Robert N. M. Watson
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.\" Copyright (c) 2014 Benjamin J. Kaduk
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 26, 2014
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.Dt SOCKET 9
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.Os
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.Sh NAME
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.Nm socket
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.Nd "kernel socket interface"
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.Sh SYNOPSIS
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.In sys/socket.h
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.In sys/socketvar.h
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.Ft void
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.Fn soabort "struct socket *so"
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.Ft int
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.Fn soaccept "struct socket *so" "struct sockaddr **nam"
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.Ft int
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.Fn socheckuid "struct socket *so" "uid_t uid"
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.Ft int
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.Fn sobind "struct socket *so" "struct sockaddr *nam" "struct thread *td"
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.Ft void
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.Fn soclose "struct socket *so"
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.Ft int
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.Fn soconnect "struct socket *so" "struct sockaddr *nam" "struct thread *td"
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.Ft int
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.Fo socreate
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.Fa "int dom" "struct socket **aso" "int type" "int proto"
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.Fa "struct ucred *cred" "struct thread *td"
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.Fc
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.Ft int
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.Fn sodisconnect "struct socket *so"
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.Ft struct sockaddr *
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.Fn sodupsockaddr "const struct sockaddr *sa" "int mflags"
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.Ft void
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.Fn sofree "struct socket *so"
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.Ft void
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.Fn sohasoutofband "struct socket *so"
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.Ft int
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.Fn solisten "struct socket *so" "int backlog" "struct thread *td"
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.Ft void
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.Fn solisten_proto "struct socket *so" "int backlog"
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.Ft int
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.Fn solisten_proto_check "struct socket *so"
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.Ft struct socket *
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.Fn sonewconn "struct socket *head" "int connstatus"
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.Ft int
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.Fo sopoll
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.Fa "struct socket *so" "int events" "struct ucred *active_cred"
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.Fa "struct thread *td"
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.Fc
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.Ft int
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.Fo sopoll_generic
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.Fa "struct socket *so" "int events" "struct ucred *active_cred"
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.Fa "struct thread *td"
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.Fc
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.Ft int
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.Fo soreceive
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.Fa "struct socket *so" "struct sockaddr **psa" "struct uio *uio"
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.Fa "struct mbuf **mp0" "struct mbuf **controlp" "int *flagsp"
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.Fc
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.Ft int
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.Fo soreceive_stream
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.Fa "struct socket *so" "struct sockaddr **paddr"
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.Fa "struct uio *uio" "struct mbuf **mp0" "struct mbuf **controlp"
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.Fa "int *flagsp"
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.Fc
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.Ft int
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.Fo soreceive_dgram
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.Fa "struct socket *so" "struct sockaddr **paddr"
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.Fa "struct uio *uio" "struct mbuf **mp0" "struct mbuf **controlp"
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.Fa "int *flagsp"
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.Fc
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.Ft int
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.Fo soreceive_generic
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.Fa "struct socket *so" "struct sockaddr **paddr"
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.Fa "struct uio *uio" "struct mbuf **mp0" "struct mbuf **controlp"
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.Fa "int *flagsp"
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.Fc
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.Ft int
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.Fn soreserve "struct socket *so" "u_long sndcc" "u_long rcvcc"
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.Ft void
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.Fn sorflush "struct socket *so"
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.Ft int
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.Fo sosend
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.Fa "struct socket *so" "struct sockaddr *addr" "struct uio *uio"
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.Fa "struct mbuf *top" "struct mbuf *control" "int flags" "struct thread *td"
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.Fc
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.Ft int
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.Fo sosend_dgram
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.Fa "struct socket *so" "struct sockaddr *addr"
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.Fa "struct uio *uio" "struct mbuf *top" "struct mbuf *control"
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.Fa "int flags" "struct thread *td"
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.Fc
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.Ft int
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.Fo sosend_generic
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.Fa "struct socket *so" "struct sockaddr *addr"
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.Fa "struct uio *uio" "struct mbuf *top" "struct mbuf *control"
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.Fa "int flags" "struct thread *td"
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.Fc
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.Ft int
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.Fn soshutdown "struct socket *so" "int how"
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.Ft void
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.Fn sotoxsocket "struct socket *so" "struct xsocket *xso"
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.Ft void
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.Fn soupcall_clear "struct socket *so" "int which"
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.Ft void
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.Fo soupcall_set
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.Fa "struct socket *so" "int which"
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.Fa "int (*func)(struct socket *, void *, int)" "void *arg"
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.Fc
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.Ft void
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.Fn sowakeup "struct socket *so" "struct sockbuf *sb"
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.In sys/sockopt.h
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.Ft int
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.Fn sosetopt "struct socket *so" "struct sockopt *sopt"
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.Ft int
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.Fn sogetopt "struct socket *so" "struct sockopt *sopt"
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.Ft int
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.Fn sooptcopyin "struct sockopt *sopt" "void *buf" "size_t len" "size_t minlen"
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.Ft int
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.Fn sooptcopyout "struct sockopt *sopt" "const void *buf" "size_t len"
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.Sh DESCRIPTION
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The kernel
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.Nm
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programming interface permits in-kernel consumers to interact with
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local and network socket objects in a manner similar to that permitted using
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the
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.Xr socket 2
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user API.
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These interfaces are appropriate for use by distributed file systems and
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other network-aware kernel services.
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While the user API operates on file descriptors, the kernel interfaces
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operate directly on
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.Vt "struct socket"
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pointers.
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Some portions of the kernel API exist only to implement the user API,
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and are not expected to be used by kernel code.
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The portions of the socket API used by socket consumers and
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implementations of network protocols will differ; some routines
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are only useful for protocol implementors.
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.Pp
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Except where otherwise indicated,
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.Nm
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functions may sleep, and are not appropriate for use in an
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.Xr ithread 9
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context or while holding non-sleepable kernel locks.
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.Ss Creating and Destroying Sockets
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A new socket may be created using
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.Fn socreate .
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As with
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.Xr socket 2 ,
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arguments specify the requested domain, type, and protocol via
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.Fa dom , type ,
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and
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.Fa proto .
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The socket is returned via
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.Fa aso
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on success.
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In addition, the credential used to authorize operations associated with the
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socket will be passed via
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.Fa cred
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(and will be cached for the lifetime of the socket), and the thread
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performing the operation via
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.Fa td .
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.Em Warning :
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authorization of the socket creation operation will be performed
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using the thread credential for some protocols (such as raw sockets).
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.Pp
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Sockets may be closed and freed using
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.Fn soclose ,
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which has similar semantics to
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.Xr close 2 .
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.Pp
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In certain circumstances, it is appropriate to destroy a socket without
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waiting for it to disconnect, for which
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.Fn soabort
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is used.
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This is only appropriate for incoming connections which are in a
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partially connected state.
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It must be called on an unreferenced socket, by the thread which
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removed the socket from its listen queue, to prevent races.
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It will call into protocol code, so no socket locks may be held
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over the call.
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The caller of
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.Fn soabort
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is responsible for setting the VNET context.
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The normal path to freeing a socket is
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.Fn sofree ,
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which handles reference counting on the socket.
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It should be called whenever a reference is released, and also whenever
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reference flags are cleared in socket or protocol code.
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Calls to
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.Fn sofree
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should not be made from outside the socket layer; outside callers
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should use
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.Fn soclose
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instead.
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.Ss Connections and Addresses
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The
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.Fn sobind
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function is equivalent to the
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.Xr bind 2
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system call, and binds the socket
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.Fa so
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to the address
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.Fa nam .
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The operation would be authorized using the credential on thread
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.Fa td .
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.Pp
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The
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.Fn soconnect
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function is equivalent to the
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.Xr connect 2
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system call, and initiates a connection on the socket
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.Fa so
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to the address
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.Fa nam .
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The operation will be authorized using the credential on thread
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.Fa td .
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Unlike the user system call,
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.Fn soconnect
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returns immediately; the caller may
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.Xr msleep 9
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on
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.Fa so->so_timeo
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while holding the socket mutex and waiting for the
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.Dv SS_ISCONNECTING
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flag to clear or
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.Fa so->so_error
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to become non-zero.
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If
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.Fn soconnect
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fails, the caller must manually clear the
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.Dv SS_ISCONNECTING
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flag.
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.Pp
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A call to
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.Fn sodisconnect
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disconnects the socket without closing it.
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.Pp
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The
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.Fn soshutdown
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function is equivalent to the
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.Xr shutdown 2
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system call, and causes part or all of a connection on a socket to be closed
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down.
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.Pp
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Sockets are transitioned from non-listening status to listening with
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.Fn solisten .
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.Ss Socket Options
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The
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.Fn sogetopt
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function is equivalent to the
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.Xr getsockopt 2
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system call, and retrieves a socket option on socket
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.Fa so .
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The
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.Fn sosetopt
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function is equivalent to the
|
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.Xr setsockopt 2
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system call, and sets a socket option on socket
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.Fa so .
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.Pp
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The second argument in both
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.Fn sogetopt
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and
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.Fn sosetopt
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is the
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.Fa sopt
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pointer to a
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.Vt "struct sopt"
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describing the socket option operation.
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The caller-allocated structure must be zeroed, and then have its fields
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initialized to specify socket option operation arguments:
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.Bl -tag -width ".Va sopt_valsize"
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.It Va sopt_dir
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Set to
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.Dv SOPT_SET
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or
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.Dv SOPT_GET
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depending on whether this is a get or set operation.
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.It Va sopt_level
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Specify the level in the network stack the operation is targeted at; for
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example,
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.Dv SOL_SOCKET .
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.It Va sopt_name
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Specify the name of the socket option to set.
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.It Va sopt_val
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Kernel space pointer to the argument value for the socket option.
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.It Va sopt_valsize
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Size of the argument value in bytes.
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.El
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.Ss Socket Upcalls
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In order for the owner of a socket to be notified when the socket
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is ready to send or receive data, an upcall may be registered on
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the socket.
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The upcall is a function that will be called by the socket framework
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when a socket buffer associated with the given socket is ready for
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reading or writing.
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.Fn soupcall_set
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is used to register a socket upcall.
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The function
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.Va func
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is registered, and the pointer
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.Va arg
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will be passed as its second argument when it is called by the framework.
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The possible values for
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.Va which
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are
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.Dv SO_RCV
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and
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.Dv SO_SND ,
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which register upcalls for receive and send events, respectively.
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The upcall function
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.Fn func
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must return either
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.Dv SU_OK
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or
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.Dv SU_ISCONNECTED ,
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depending on whether or not a call to
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.Xr soisconnected
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should be made by the socket framework after the upcall returns.
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The upcall
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.Va func
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cannot call
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.Xr soisconnected
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itself due to lock ordering with the socket buffer lock.
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Only
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.Dv SO_RCV
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upcalls should return
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.Dv SU_ISCONNECTED .
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When a
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.Dv SO_RCV
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upcall returns
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.Dv SU_ISCONNECTED ,
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the upcall will be removed from the socket.
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.Pp
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Upcalls are removed from their socket by
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.Fn soupcall_clear .
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The
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.Va which
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argument again specifies whether the sending or receiving upcall is to
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be cleared, with
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.Dv SO_RCV
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or
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.Dv SO_SND .
|
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.Ss Socket I/O
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|
The
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.Fn soreceive
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function is equivalent to the
|
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.Xr recvmsg 2
|
|
system call, and attempts to receive bytes of data from the socket
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.Fa so ,
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optionally blocking awaiting for data if none is ready to read.
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Data may be retrieved directly to kernel or user memory via the
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.Fa uio
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argument, or as an mbuf chain returned to the caller via
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.Fa mp0 ,
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avoiding a data copy.
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The
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.Fa uio
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must always be
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.Pf non- Dv NULL .
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If
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.Fa mp0
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is
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.Pf non- Dv NULL ,
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only the
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.Pf uio_resid
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of
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.Fa uio
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is used.
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The caller may optionally retrieve a socket address on a protocol with the
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.Dv PR_ADDR
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capability by providing storage via
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.Pf non- Dv NULL
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.Fa psa
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argument.
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|
The caller may optionally retrieve control data mbufs via a
|
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.Pf non- Dv NULL
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.Fa controlp
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argument.
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Optional flags may be passed to
|
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.Fn soreceive
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via a
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.Pf non- Dv NULL
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.Fa flagsp
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argument, and use the same flag name space as the
|
|
.Xr recvmsg 2
|
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system call.
|
|
.Pp
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The
|
|
.Fn sosend
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function is equivalent to the
|
|
.Xr sendmsg 2
|
|
system call, and attempts to send bytes of data via the socket
|
|
.Fa so ,
|
|
optionally blocking if data cannot be immediately sent.
|
|
Data may be sent directly from kernel or user memory via the
|
|
.Fa uio
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argument, or as an mbuf chain via
|
|
.Fa top ,
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|
avoiding a data copy.
|
|
Only one of the
|
|
.Fa uio
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|
or
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|
.Fa top
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|
pointers may be
|
|
.Pf non- Dv NULL .
|
|
An optional destination address may be specified via a
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|
.Pf non- Dv NULL
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|
.Fa addr
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|
argument, which may result in an implicit connect if supported by the
|
|
protocol.
|
|
The caller may optionally send control data mbufs via a
|
|
.Pf non- Dv NULL
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|
.Fa control
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argument.
|
|
Flags may be passed to
|
|
.Fn sosend
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|
using the
|
|
.Fa flags
|
|
argument, and use the same flag name space as the
|
|
.Xr sendmsg 2
|
|
system call.
|
|
.Pp
|
|
Kernel callers running in
|
|
.Xr ithread 9
|
|
context, or with a mutex held, will wish to use non-blocking sockets and pass
|
|
the
|
|
.Dv MSG_DONTWAIT
|
|
flag in order to prevent these functions from sleeping.
|
|
.Pp
|
|
A socket can be queried for readability, writability, out-of-band data,
|
|
or end-of-file using
|
|
.Fn sopoll .
|
|
The possible values for
|
|
.Va events
|
|
are as for
|
|
.Xr poll 2 ,
|
|
with symbolic values
|
|
.Dv POLLIN ,
|
|
.Dv POLLPRI ,
|
|
.Dv POLLOUT ,
|
|
.Dv POLLRDNORM ,
|
|
.Dv POLLWRNORM ,
|
|
.Dv POLLRDBAND ,
|
|
and
|
|
.Dv POLLINGEOF
|
|
taken from
|
|
.In sys/poll.h .
|
|
.Pp
|
|
Calls to
|
|
.Fn soaccept
|
|
pass through to the protocol's accept routine to accept an incoming connection.
|
|
.Ss Socket Utility Functions
|
|
The uid of a socket's credential may be compared against a
|
|
.Va uid
|
|
with
|
|
.Fn socheckuid .
|
|
.Pp
|
|
A copy of an existing
|
|
.Vt struct sockaddr
|
|
may be made using
|
|
.Fn sodupsockaddr .
|
|
.Pp
|
|
Protocol implementations notify the socket layer of the arrival of
|
|
out-of-band data using
|
|
.Fn sohasoutofband ,
|
|
so that the socket layer can notify socket consumers of the available data.
|
|
.Pp
|
|
An
|
|
.Dq external-format
|
|
version of a
|
|
.Vt struct socket
|
|
can be created using
|
|
.Fn sotoxsocket ,
|
|
suitable for isolating user code from changes in the kernel structure.
|
|
.Ss Protocol Implementations
|
|
Protocols must supply an implementation for
|
|
.Fn solisten ;
|
|
such protocol implementations can call back into the socket layer using
|
|
.Fn solisten_proto_check
|
|
and
|
|
.Fn solisten_proto
|
|
to check and set the socket-layer listen state.
|
|
These callbacks are provided so that the protocol implementation
|
|
can order the socket layer and protocol locks as necessary.
|
|
Protocols must supply an implementation of
|
|
.Fn soreceive ;
|
|
the functions
|
|
.Fn soreceive_stream ,
|
|
.Fn soreceive_dgram ,
|
|
and
|
|
.Fn soreceive_generic
|
|
are supplied for use by such implementations.
|
|
.Pp
|
|
Protocol implementations can use
|
|
.Fn sonewconn
|
|
to create a socket and attach protocol state to that socket.
|
|
This can be used to create new sockets available for
|
|
.Fn soaccept
|
|
on a listen socket.
|
|
The returned socket has a reference count of zero.
|
|
.Pp
|
|
Protocols must supply an implementation for
|
|
.Fn sopoll ;
|
|
.Fn sopoll_generic
|
|
is provided for the use by protocol implementations.
|
|
.Pp
|
|
The functions
|
|
.Fn sosend_dgram
|
|
and
|
|
.Fn sosend_generic
|
|
are supplied to assist in protocol implementations of
|
|
.Fn sosend .
|
|
.Pp
|
|
When a protocol creates a new socket structure, it is necessary to
|
|
reserve socket buffer space for that socket, by calling
|
|
.Fn soreserve .
|
|
The rough inverse of this reservation is performed by
|
|
.Fn sorflush ,
|
|
which is called automatically by the socket framework.
|
|
.Pp
|
|
When a protocol needs to wake up threads waiting for the socket to
|
|
become ready to read or write, variants of
|
|
.Fn sowakeup
|
|
are used.
|
|
The
|
|
.Fn sowakeup
|
|
function should not be called directly by protocol code, instead use the
|
|
wrappers
|
|
.Fn sorwakeup ,
|
|
.Fn sorwakeup_locked ,
|
|
.Fn sowwakeup ,
|
|
and
|
|
.Fn sowwakeup_locked
|
|
for readers and writers, with the corresponding socket buffer lock
|
|
not already locked, or already held, respectively.
|
|
.Pp
|
|
The functions
|
|
.Fn sooptcopyin
|
|
and
|
|
.Fn sooptcopyout
|
|
are useful for transferring
|
|
.Vt struct sockopt
|
|
data between user and kernel code.
|
|
.Sh SEE ALSO
|
|
.Xr bind 2 ,
|
|
.Xr close 2 ,
|
|
.Xr connect 2 ,
|
|
.Xr getsockopt 2 ,
|
|
.Xr recv 2 ,
|
|
.Xr send 2 ,
|
|
.Xr setsockopt 2 ,
|
|
.Xr shutdown 2 ,
|
|
.Xr socket 2 ,
|
|
.Xr ng_ksocket 4 ,
|
|
.Xr ithread 9 ,
|
|
.Xr msleep 9 ,
|
|
.Xr ucred 9
|
|
.Sh HISTORY
|
|
The
|
|
.Xr socket 2
|
|
system call appeared in
|
|
.Bx 4.2 .
|
|
This manual page was introduced in
|
|
.Fx 7.0 .
|
|
.Sh AUTHORS
|
|
This manual page was written by
|
|
.An Robert Watson
|
|
and
|
|
.An Benjamin Kaduk .
|
|
.Sh BUGS
|
|
The use of explicitly passed credentials, credentials hung from explicitly
|
|
passed threads, the credential on
|
|
.Dv curthread ,
|
|
and the cached credential from
|
|
socket creation time is inconsistent, and may lead to unexpected behaviour.
|
|
It is possible that several of the
|
|
.Fa td
|
|
arguments should be
|
|
.Fa cred
|
|
arguments, or simply not be present at all.
|
|
.Pp
|
|
The caller may need to manually clear
|
|
.Dv SS_ISCONNECTING
|
|
if
|
|
.Fn soconnect
|
|
returns an error.
|
|
.Pp
|
|
The
|
|
.Dv MSG_DONTWAIT
|
|
flag is not implemented for
|
|
.Fn sosend ,
|
|
and may not always work with
|
|
.Fn soreceive
|
|
when zero copy sockets are enabled.
|
|
.Pp
|
|
This manual page does not describe how to register socket upcalls or monitor
|
|
a socket for readability/writability without using blocking I/O.
|
|
.Pp
|
|
The
|
|
.Fn soref
|
|
and
|
|
.Fn sorele
|
|
functions are not described, and in most cases should not be used, due to
|
|
confusing and potentially incorrect interactions when
|
|
.Fn sorele
|
|
is last called after
|
|
.Fn soclose .
|