.\"	$NetBSD: sockopt.9,v 1.11 2018/01/04 01:42:25 christos Exp $
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.\" Copyright (c) 2008 Iain Hibbert
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.Dd January 3, 2018
.Dt SOCKOPT 9
.Os
.Sh NAME
.Nm sockopt_init ,
.Nm sockopt_destroy ,
.Nm sockopt_get ,
.Nm sockopt_getint ,
.Nm sockopt_set ,
.Nm sockopt_setint
.Nd socket options handling
.Sh SYNOPSIS
.In sys/socketvar.h
.Ft void
.Fn sockopt_init "struct sockopt *sopt" "int level" "int name" "size_t size"
.Ft void
.Fn sockopt_destroy "struct sockopt *sopt"
.Ft int
.Fn sockopt_get "struct sockopt *sopt" "void *value" "size_t size"
.Ft int
.Fn sockopt_getint "struct sockopt *sopt" "int *value"
.Ft int
.Fn sockopt_set "struct sockopt *sopt" "const void *value" "size_t size"
.Ft int
.Fn sockopt_setint "struct sockopt *sopt" "int value"
.Sh DESCRIPTION
The
.Ft sockopt
structure is used to pass a socket option and associated value:
.Bd -literal -offset indent
struct sockopt {
	int		sopt_level;		/* option level */
	int		sopt_name;		/* option name */
	size_t		sopt_size;		/* data length */
	size_t		sopt_retsize;		/* returned data length */
	void *		sopt_data;		/* data pointer */
	uint8_t		sopt_buf[sizeof(int)];	/* internal storage */
};
.Ed
.Pp
The internal storage is used for the common case of values up to integer
size so that memory allocation is not required and sopt_data will point
to this in that case.
.Pp
Rather than provide accessor functions, the
.Ft sockopt
structure is public and the contents are expected to be internally
consistent, but the normal practice would be to use the appropriate methods
for storage and retrieval of values where a known datatype is expected,
as the size will be verified.
.Pp
Note: a sockopt structure may only be used for a single level/name/size
combination.
If the structure is to be re-used, it must be destroyed and re-initialized
with the new values.
.Sh OPTIONS
.Bl -tag -width xxxx
.It Cd "options DIAGNOSTIC"
Kernels compiled with the
.Dv DIAGNOSTIC
option will perform basic sanity checks on socket options operations.
.El
.Sh FUNCTIONS
.Bl -tag -width xxxx
.It Fn sockopt_init "sopt" "level" "name" "size"
Initialise sockopt storage.
If
.Ar size
is given,
.Fn sockopt_init
will arrange for sopt_data to point to a buffer of
.Ar size
bytes for the sockopt value.
Where memory needs to be allocated to satisfy this,
.Fn sockopt_init
may sleep.
.It Fn sockopt_destroy "sopt"
Destroy sockopt storage, releasing any allocated memory.
.It Fn sockopt_get "sopt" "value" "size"
Copy out sockopt value.
Will return
.Er EINVAL
if an incorrect data size is given.
.It Fn sockopt_getint "sopt" "value"
Common case of get sockopt integer value.
Will return
.Er EINVAL
if sockopt does not contain an integer sized value.
.It Fn sockopt_set "sopt" "value" "size"
Copy in sockopt value.
The sockopt structure must contain a data field of
.Ar size
bytes or be previously unset, in which case a data buffer may be
allocated using
.Xr kmem_alloc 9
with the
.Dv KM_NOSLEEP
flag which may cause
.Fn sockopt_set
to return
.Er ENOMEM .
.Pp
Note: If you need to use
.Fn sockopt_set
in a context where memory allocation may be required and you do not wish to
contemplate failure, the sockopt structure can be initialised in a more suitable
context using
.Fn sockopt_init
which will not fail.
.It Fn sockopt_setint "sopt" "value"
Common case of set sockopt integer value.
The sockopt structure must contain an int sized data field or be previously
unset, in which case the data pointer will be set to the internal storage.
.El
.Sh CODE REFERENCES
The function prototypes and sockopt structure are defined in the
.Pa sys/sys/socketvar.h
header file, and the socket options implementation is in
.Pa sys/kern/uipc_socket.c .
.Sh SEE ALSO
.Xr errno 2 ,
.Xr kmem 9
.Sh HISTORY
The socket options KPI was inspired by a similar KPI in
.Fx
and
first appeared in
.Nx 5.0 .