.\" $OpenBSD: if_get.9,v 1.2 2015/12/08 18:35:51 jmc Exp $
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.\" Copyright (c) 2015 Martin Pieuchot
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.Dd $Mdocdate: December 8 2015 $
.Dt IF_GET 9
.Os
.Sh NAME
.Nm if_get ,
.Nm if_put
.Nd get an interface pointer from an interface index
.Sh SYNOPSIS
.In net/if.h
.Ft struct ifnet *
.Fn if_get "unsigned int ifidx"
.Ft void
.Fn if_put "struct ifnet *ifp"
.Sh DESCRIPTION
The
.Fn if_get
function returns a pointer to the interface descriptor corresponding to the
unique index
.Fa ifidx .
This descriptor is guaranteed to be valid until
.Fn if_put
is called on the returned pointer.
.Pp
The index value
.Dv 0
is never associated with an interface descriptor and can be used to determine if
an interface index is valid or not.
.Pp
The
.Fn if_put
function releases a reference on the interface descriptor pointed by
.Fa ifp .
If
.Fa ifp
is a
.Dv NULL
pointer, no action occurs.
.Sh CONTEXT
.Fn if_get ,
and
.Fn if_put
can be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Fn if_get
returns a pointer to an interface descriptor if the index is valid, otherwise
.Dv NULL .