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https://github.com/freebsd/freebsd-src
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![Brooks Davis](/assets/img/avatar_default.png)
Remove core system call implementations and documentation to lib/libsys and lib/libsys/<arch> from lib/libc/sys and lib/libc/<arch>/<sys>. Update paths to allow libc to find them in their new home. Reviewed by: kib, emaste, imp Pull Request: https://github.com/freebsd/freebsd-src/pull/908
623 lines
18 KiB
Groff
623 lines
18 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. 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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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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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.Dd February 8, 2021
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.Dt GETSOCKOPT 2
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.Os
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.Sh NAME
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.Nm getsockopt ,
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.Nm setsockopt
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.Nd get and set options on sockets
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.Ft int
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.Fn getsockopt "int s" "int level" "int optname" "void * restrict optval" "socklen_t * restrict optlen"
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.Ft int
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.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
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.Sh DESCRIPTION
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The
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.Fn getsockopt
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and
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.Fn setsockopt
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system calls
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manipulate the
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.Em options
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associated with a socket.
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Options may exist at multiple
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protocol levels; they are always present at the uppermost
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.Dq socket
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level.
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.Pp
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When manipulating socket options the level at which the
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option resides and the name of the option must be specified.
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To manipulate options at the socket level,
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.Fa level
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is specified as
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.Dv SOL_SOCKET .
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To manipulate options at any
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other level the protocol number of the appropriate protocol
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controlling the option is supplied.
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For example,
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to indicate that an option is to be interpreted by the
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.Tn TCP
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protocol,
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.Fa level
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should be set to the protocol number of
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.Tn TCP ;
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see
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.Xr getprotoent 3 .
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.Pp
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The
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.Fa optval
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and
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.Fa optlen
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arguments
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are used to access option values for
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.Fn setsockopt .
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For
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.Fn getsockopt
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they identify a buffer in which the value for the
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requested option(s) are to be returned.
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For
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.Fn getsockopt ,
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.Fa optlen
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is a value-result argument, initially containing the
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size of the buffer pointed to by
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.Fa optval ,
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and modified on return to indicate the actual size of
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the value returned.
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If no option value is
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to be supplied or returned,
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.Fa optval
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may be NULL.
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.Pp
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The
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.Fa optname
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argument
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and any specified options are passed uninterpreted to the appropriate
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protocol module for interpretation.
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The include file
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.In sys/socket.h
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contains definitions for
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socket level options, described below.
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Options at other protocol levels vary in format and
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name; consult the appropriate entries in
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section
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4 of the manual.
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.Pp
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Most socket-level options utilize an
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.Vt int
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argument for
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.Fa optval .
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For
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.Fn setsockopt ,
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the argument should be non-zero to enable a boolean option,
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or zero if the option is to be disabled.
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.Dv SO_LINGER
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uses a
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.Vt "struct linger"
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argument, defined in
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.In sys/socket.h ,
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which specifies the desired state of the option and the
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linger interval (see below).
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.Dv SO_SNDTIMEO
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and
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.Dv SO_RCVTIMEO
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use a
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.Vt "struct timeval"
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argument, defined in
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.In sys/time.h .
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.Pp
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The following options are recognized at the socket level.
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For protocol-specific options, see protocol manual pages,
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e.g.
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.Xr ip 4
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or
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.Xr tcp 4 .
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Except as noted, each may be examined with
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.Fn getsockopt
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and set with
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.Fn setsockopt .
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.Bl -column SO_ACCEPTFILTER -offset indent
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.It Dv SO_DEBUG Ta "enables recording of debugging information"
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.It Dv SO_REUSEADDR Ta "enables local address reuse"
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.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
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.It Dv SO_REUSEPORT_LB Ta "enables duplicate address and port bindings with load balancing"
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.It Dv SO_KEEPALIVE Ta "enables keep connections alive"
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.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
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.It Dv SO_LINGER Ta "linger on close if data present"
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.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
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.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
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.It Dv SO_SNDBUF Ta "set buffer size for output"
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.It Dv SO_RCVBUF Ta "set buffer size for input"
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.It Dv SO_SNDLOWAT Ta "set minimum count for output"
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.It Dv SO_RCVLOWAT Ta "set minimum count for input"
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.It Dv SO_SNDTIMEO Ta "set timeout value for output"
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.It Dv SO_RCVTIMEO Ta "set timeout value for input"
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.It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
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.It Dv SO_NOSIGPIPE Ta
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controls generation of
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.Dv SIGPIPE
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for the socket
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.It Dv SO_TIMESTAMP Ta "enables reception of a timestamp with datagrams"
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.It Dv SO_BINTIME Ta "enables reception of a timestamp with datagrams"
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.It Dv SO_ACCEPTCONN Ta "get listening status of the socket (get only)"
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.It Dv SO_DOMAIN Ta "get the domain of the socket (get only)"
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.It Dv SO_TYPE Ta "get the type of the socket (get only)"
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.It Dv SO_PROTOCOL Ta "get the protocol number for the socket (get only)"
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.It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
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.It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
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.It Dv SO_RERROR Ta "enables receive error reporting"
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.It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
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.El
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.Pp
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The following options are recognized in
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.Fx :
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.Bl -column SO_LISTENINCQLEN -offset indent
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.It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
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.It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
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.It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
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.It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
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.It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
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.It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
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.It Dv SO_TS_CLOCK Ta "set specific format of timestamp returned by SO_TIMESTAMP"
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.It Dv SO_MAX_PACING_RATE Ta "set the maximum transmit rate in bytes per second for the socket"
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.It Dv SO_NO_OFFLOAD Ta "disables protocol offloads"
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.It Dv SO_NO_DDP Ta "disables direct data placement offload"
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.El
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.Pp
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.Dv SO_DEBUG
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enables debugging in the underlying protocol modules.
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.Pp
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.Dv SO_REUSEADDR
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indicates that the rules used in validating addresses supplied
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in a
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.Xr bind 2
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system call should allow reuse of local addresses.
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.Pp
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.Dv SO_REUSEPORT
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allows completely duplicate bindings by multiple processes
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if they all set
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.Dv SO_REUSEPORT
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before binding the port.
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This option permits multiple instances of a program to each
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receive UDP/IP multicast or broadcast datagrams destined for the bound port.
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.Pp
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.Dv SO_REUSEPORT_LB
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allows completely duplicate bindings by multiple sockets
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if they all set
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.Dv SO_REUSEPORT_LB
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before binding the port.
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Incoming TCP and UDP connections are distributed among the participating
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listening sockets based on a hash function of local port number, and foreign IP
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address and port number.
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A maximum of 256 sockets can be bound to the same load-balancing group.
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.Pp
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.Dv SO_KEEPALIVE
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enables the
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periodic transmission of messages on a connected socket.
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Should the
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connected party fail to respond to these messages, the connection is
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considered broken and processes using the socket are notified via a
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.Dv SIGPIPE
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signal when attempting to send data.
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|
.Pp
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.Dv SO_DONTROUTE
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indicates that outgoing messages should
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bypass the standard routing facilities.
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|
Instead, messages are directed
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to the appropriate network interface according to the network portion
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of the destination address.
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.Pp
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.Dv SO_LINGER
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controls the action taken when unsent messages
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are queued on socket and a
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.Xr close 2
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is performed.
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|
If the socket promises reliable delivery of data and
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.Dv SO_LINGER
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is set,
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the system will block the process on the
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.Xr close 2
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attempt until it is able to transmit the data or until it decides it
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is unable to deliver the information (a timeout period, termed the
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linger interval, is specified in seconds in the
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.Fn setsockopt
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system call when
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.Dv SO_LINGER
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is requested).
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|
If
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.Dv SO_LINGER
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|
is disabled and a
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|
.Xr close 2
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|
is issued, the system will process the close in a manner that allows
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the process to continue as quickly as possible.
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|
.Pp
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|
The option
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.Dv SO_BROADCAST
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|
requests permission to send broadcast datagrams
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on the socket.
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|
Broadcast was a privileged operation in earlier versions of the system.
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|
.Pp
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|
With protocols that support out-of-band data, the
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.Dv SO_OOBINLINE
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option
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requests that out-of-band data be placed in the normal data input queue
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as received; it will then be accessible with
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|
.Xr recv 2
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|
or
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|
.Xr read 2
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|
calls without the
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.Dv MSG_OOB
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flag.
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|
Some protocols always behave as if this option is set.
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|
.Pp
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.Dv SO_SNDBUF
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and
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.Dv SO_RCVBUF
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are options to adjust the normal
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buffer sizes allocated for output and input buffers, respectively.
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The buffer size may be increased for high-volume connections,
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or may be decreased to limit the possible backlog of incoming data.
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The system places an absolute maximum on these values, which is accessible
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through the
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.Xr sysctl 3
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MIB variable
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.Dq Li kern.ipc.maxsockbuf .
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|
.Pp
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|
.Dv SO_SNDLOWAT
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|
is an option to set the minimum count for output operations.
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|
Most output operations process all of the data supplied
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by the call, delivering data to the protocol for transmission
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and blocking as necessary for flow control.
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Nonblocking output operations will process as much data as permitted
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subject to flow control without blocking, but will process no data
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if flow control does not allow the smaller of the low water mark value
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or the entire request to be processed.
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A
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.Xr select 2
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|
operation testing the ability to write to a socket will return true
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only if the low water mark amount could be processed.
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|
The default value for
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.Dv SO_SNDLOWAT
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|
is set to a convenient size for network efficiency, often 1024.
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.Pp
|
|
.Dv SO_RCVLOWAT
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|
is an option to set the minimum count for input operations.
|
|
In general, receive calls will block until any (non-zero) amount of data
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is received, then return with the smaller of the amount available or the amount
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requested.
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|
The default value for
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.Dv SO_RCVLOWAT
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is 1.
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If
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.Dv SO_RCVLOWAT
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is set to a larger value, blocking receive calls normally
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wait until they have received the smaller of the low water mark value
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or the requested amount.
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Receive calls may still return less than the low water mark if an error
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occurs, a signal is caught, or the type of data next in the receive queue
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is different from that which was returned.
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|
.Pp
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.Dv SO_SNDTIMEO
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|
is an option to set a timeout value for output operations.
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|
It accepts a
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.Vt "struct timeval"
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argument with the number of seconds and microseconds
|
|
used to limit waits for output operations to complete.
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|
If a send operation has blocked for this much time,
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it returns with a partial count
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|
or with the error
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.Er EWOULDBLOCK
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if no data were sent.
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In the current implementation, this timer is restarted each time additional
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data are delivered to the protocol,
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implying that the limit applies to output portions ranging in size
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from the low water mark to the high water mark for output.
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.Pp
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.Dv SO_RCVTIMEO
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is an option to set a timeout value for input operations.
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It accepts a
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.Vt "struct timeval"
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argument with the number of seconds and microseconds
|
|
used to limit waits for input operations to complete.
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|
In the current implementation, this timer is restarted each time additional
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data are received by the protocol,
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and thus the limit is in effect an inactivity timer.
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If a receive operation has been blocked for this much time without
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receiving additional data, it returns with a short count
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or with the error
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.Er EWOULDBLOCK
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if no data were received.
|
|
.Pp
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.Dv SO_SETFIB
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can be used to over-ride the default FIB (routing table) for the given socket.
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|
The value must be from 0 to one less than the number returned from
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the sysctl
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.Em net.fibs .
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|
.Pp
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.Dv SO_USER_COOKIE
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|
can be used to set the uint32_t so_user_cookie field in the socket.
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|
The value is an uint32_t, and can be used in the kernel code that
|
|
manipulates traffic related to the socket.
|
|
The default value for the field is 0.
|
|
As an example, the value can be used as the skipto target or
|
|
pipe number in
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.Nm ipfw/dummynet .
|
|
.Pp
|
|
.Dv SO_ACCEPTFILTER
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|
places an
|
|
.Xr accept_filter 9
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|
on the socket,
|
|
which will filter incoming connections
|
|
on a listening stream socket before being presented for
|
|
.Xr accept 2 .
|
|
Once more,
|
|
.Xr listen 2
|
|
must be called on the socket before
|
|
trying to install the filter on it,
|
|
or else the
|
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.Fn setsockopt
|
|
system call will fail.
|
|
.Bd -literal
|
|
struct accept_filter_arg {
|
|
char af_name[16];
|
|
char af_arg[256-16];
|
|
};
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fa optval
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|
argument
|
|
should point to a
|
|
.Fa struct accept_filter_arg
|
|
that will select and configure the
|
|
.Xr accept_filter 9 .
|
|
The
|
|
.Fa af_name
|
|
argument
|
|
should be filled with the name of the accept filter
|
|
that the application wishes to place on the listening socket.
|
|
The optional argument
|
|
.Fa af_arg
|
|
can be passed to the accept
|
|
filter specified by
|
|
.Fa af_name
|
|
to provide additional configuration options at attach time.
|
|
Passing in an
|
|
.Fa optval
|
|
of NULL will remove the filter.
|
|
.Pp
|
|
The
|
|
.Dv SO_NOSIGPIPE
|
|
option controls generation of the
|
|
.Dv SIGPIPE
|
|
signal normally sent
|
|
when writing to a connected socket where the other end has been
|
|
closed returns with the error
|
|
.Er EPIPE .
|
|
.Pp
|
|
If the
|
|
.Dv SO_TIMESTAMP
|
|
or
|
|
.Dv SO_BINTIME
|
|
option is enabled on a
|
|
.Dv SOCK_DGRAM
|
|
socket, the
|
|
.Xr recvmsg 2
|
|
call may return a timestamp corresponding to when the datagram was received.
|
|
However, it may not, for example due to a resource shortage.
|
|
The
|
|
.Va msg_control
|
|
field in the
|
|
.Vt msghdr
|
|
structure points to a buffer that contains a
|
|
.Vt cmsghdr
|
|
structure followed by a
|
|
.Vt "struct timeval"
|
|
for
|
|
.Dv SO_TIMESTAMP
|
|
and
|
|
.Vt "struct bintime"
|
|
for
|
|
.Dv SO_BINTIME .
|
|
The
|
|
.Vt cmsghdr
|
|
fields have the following values for TIMESTAMP by default:
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(struct timeval));
|
|
cmsg_level = SOL_SOCKET;
|
|
cmsg_type = SCM_TIMESTAMP;
|
|
.Ed
|
|
.Pp
|
|
and for
|
|
.Dv SO_BINTIME :
|
|
.Bd -literal
|
|
cmsg_len = CMSG_LEN(sizeof(struct bintime));
|
|
cmsg_level = SOL_SOCKET;
|
|
cmsg_type = SCM_BINTIME;
|
|
.Ed
|
|
.Pp
|
|
Additional timestamp types are available by following
|
|
.Dv SO_TIMESTAMP
|
|
with
|
|
.Dv SO_TS_CLOCK ,
|
|
which requests a specific timestamp format to be returned instead of
|
|
.Dv SCM_TIMESTAMP when
|
|
.Dv SO_TIMESTAMP is enabled.
|
|
These
|
|
.Dv SO_TS_CLOCK
|
|
values are recognized in
|
|
.Fx :
|
|
.Bl -column SO_TS_CLOCK -offset indent
|
|
.It Dv SO_TS_REALTIME_MICRO Ta "realtime (SCM_TIMESTAMP, struct timeval), default"
|
|
.It Dv SO_TS_BINTIME Ta "realtime (SCM_BINTIME, struct bintime)"
|
|
.It Dv SO_TS_REALTIME Ta "realtime (SCM_REALTIME, struct timespec)"
|
|
.It Dv SO_TS_MONOTONIC Ta "monotonic time (SCM_MONOTONIC, struct timespec)"
|
|
.El
|
|
.Pp
|
|
.Dv SO_ACCEPTCONN ,
|
|
.Dv SO_TYPE ,
|
|
.Dv SO_PROTOCOL
|
|
(and its alias
|
|
.Dv SO_PROTOTYPE )
|
|
and
|
|
.Dv SO_ERROR
|
|
are options used only with
|
|
.Fn getsockopt .
|
|
.Dv SO_ACCEPTCONN
|
|
returns whether the socket is currently accepting connections,
|
|
that is, whether or not the
|
|
.Xr listen 2
|
|
system call was invoked on the socket.
|
|
.Dv SO_TYPE
|
|
returns the type of the socket, such as
|
|
.Dv SOCK_STREAM ;
|
|
it is useful for servers that inherit sockets on startup.
|
|
.Dv SO_PROTOCOL
|
|
returns the protocol number for the socket, for
|
|
.Dv AF_INET
|
|
and
|
|
.Dv AF_INET6
|
|
address families.
|
|
.Dv SO_ERROR
|
|
returns any pending error on the socket and clears
|
|
the error status.
|
|
It may be used to check for asynchronous errors on connected
|
|
datagram sockets or for other asynchronous errors.
|
|
.Dv SO_RERROR
|
|
indicates that receive buffer overflows should be handled as errors.
|
|
Historically receive buffer overflows have been ignored and programs
|
|
could not tell if they missed messages or messages had been truncated
|
|
because of overflows.
|
|
Since programs historically do not expect to get receive overflow errors,
|
|
this behavior is not the default.
|
|
.Pp
|
|
.Dv SO_LABEL
|
|
returns the MAC label of the socket.
|
|
.Dv SO_PEERLABEL
|
|
returns the MAC label of the socket's peer.
|
|
Note that your kernel must be compiled with MAC support.
|
|
See
|
|
.Xr mac 3
|
|
for more information.
|
|
.Pp
|
|
.Dv SO_LISTENQLIMIT
|
|
returns the maximal number of queued connections, as set by
|
|
.Xr listen 2 .
|
|
.Dv SO_LISTENQLEN
|
|
returns the number of unaccepted complete connections.
|
|
.Dv SO_LISTENINCQLEN
|
|
returns the number of unaccepted incomplete connections.
|
|
.Pp
|
|
.Dv SO_MAX_PACING_RATE
|
|
instruct the socket and underlying network adapter layers to limit the
|
|
transfer rate to the given unsigned 32-bit value in bytes per second.
|
|
.Pp
|
|
.Dv SO_NO_OFFLOAD
|
|
disables support for protocol offloads.
|
|
At present, this prevents TCP sockets from using TCP offload engines.
|
|
.Dv SO_NO_DDP
|
|
disables support for a specific TCP offload known as direct data
|
|
placement (DDP).
|
|
DDP is an offload supported by Chelsio network adapters that permits
|
|
reassembled TCP data streams to be received via zero-copy in
|
|
user-supplied buffers using
|
|
.Xr aio_read 2 .
|
|
.Sh RETURN VALUES
|
|
.Rv -std
|
|
.Sh ERRORS
|
|
The
|
|
.Fn getsockopt
|
|
and
|
|
.Fn setsockopt
|
|
system calls succeed unless:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EBADF
|
|
The argument
|
|
.Fa s
|
|
is not a valid descriptor.
|
|
.It Bq Er ENOTSOCK
|
|
The argument
|
|
.Fa s
|
|
is a file, not a socket.
|
|
.It Bq Er ENOPROTOOPT
|
|
The option is unknown at the level indicated.
|
|
.It Bq Er EFAULT
|
|
The address pointed to by
|
|
.Fa optval
|
|
is not in a valid part of the process address space.
|
|
For
|
|
.Fn getsockopt ,
|
|
this error may also be returned if
|
|
.Fa optlen
|
|
is not in a valid part of the process address space.
|
|
.It Bq Er EINVAL
|
|
Installing an
|
|
.Xr accept_filter 9
|
|
on a non-listening socket was attempted.
|
|
.It Bq Er ENOMEM
|
|
A memory allocation failed that was required to service the request.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fn setsockopt
|
|
system call may also return the following error:
|
|
.Bl -tag -width Er
|
|
.It Bq Er ENOBUFS
|
|
Insufficient resources were available in the system
|
|
to perform the operation.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr ioctl 2 ,
|
|
.Xr listen 2 ,
|
|
.Xr recvmsg 2 ,
|
|
.Xr socket 2 ,
|
|
.Xr getprotoent 3 ,
|
|
.Xr mac 3 ,
|
|
.Xr sysctl 3 ,
|
|
.Xr ip 4 ,
|
|
.Xr ip6 4 ,
|
|
.Xr sctp 4 ,
|
|
.Xr tcp 4 ,
|
|
.Xr protocols 5 ,
|
|
.Xr sysctl 8 ,
|
|
.Xr accept_filter 9 ,
|
|
.Xr bintime 9
|
|
.Sh HISTORY
|
|
The
|
|
.Fn getsockopt
|
|
and
|
|
.Fn setsockopt
|
|
system calls appeared in
|
|
.Bx 4.2 .
|
|
.Sh BUGS
|
|
Several of the socket options should be handled at lower levels of the system.
|