Make a first pass at documenting the specificdata functionality.

XXX This is just a first pass, and I've probably made a ton of mistakes
XXX while reading the code!  Updates and corrections greatly appreciated.


(pgoyette)

.\"	$NetBSD: specificdata.9,v 1.1 2018/06/03 09:22:34 pgoyette Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe
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.Dd June 3, 2018
.Dt MODULE 9
.Os
.Sh NAME
.Nm specificdata ,
.Nm specificdata_domain_create ,
.Nm specificdata_domain_delete ,
.Nm specificdata_key_create ,
.Nm specificdata_key_delete ,
.Nm specificdata_init ,
.Nm specificdata_fini ,
.Nm specificdata_getspecific ,
.Nm specificdata_getspecific_unlocked ,
.Nm specificdata_setspecific ,
.Nm specificdata_setspecific_nowait
.Nd manipulate arbitrary data attached to objects
.Sh SYNOPSIS
.In sys/specificdata.h
.Ft specificdata_domain_t
.Fn specificdata_domain_create
.Ft void
.Fn specificdata_domain_delete "specificdata_domain_t sd"
.Ft int
.Fn specificdata_key_create "specificdata_domain_t sd" \
"specificdata_key_t *keyp" "specificdata_dtor_t dtor"
.Ft void
.Fn specificdata_key_delete "specificdata_domain_t sd" "specificdata_key_t key"
.Ft int
.Fn specificdata_init "specificdata_domain_t sd" "specificdata_reference *ref"
.Ft void
.Fn specificdata_fini "specificdata_domain_t sd" "specificdata_reference *ref"
.Ft "void *"
.Fn specificdata_getspecific "specificdata_domain_t sd" \
"specificdata_reference *ref" "specificdata_key_t key"
.Ft "void *"
.Fn specificdata_getspecific_unlocked "specificdata_domain_t sd" \
"specificdata_reference *ref" "specificdata_key_t key"
.Ft void
.Fn specificdata_setspecific "specificdata_domain_t sd" \
"specificdata_reference *ref" "specificdata_key_t key" "void *data"
.Ft int
.Fn specificdata_setspecific_nowait "specificdata_domain_t sd" \
"specificdata_reference *ref" "specificdata_key_t key" "void *data"
.Sh DESCRIPTION
The
.Nm
facility provides a mechanism for attaching arbitrary data to the objects
within a particular domain.
.Sh FUNCTIONS
.Bl -tag -width abcd
.It Fn specificdata_domain_create
Create a new domain.
.It Fn specificdata_domain_delete sd
Delete a domain.
.It Fn specificdata_key_create sd keyp dtor
Create a new key for the domain.
The
.Fa dtor
argument specifies a destructor which is called when an item with the
specified key is deleted.
.It Fn specificdata_key_delete sd key
Delete a key for the domain, and delete any associated values.
.It Fn specificdata_init sd ref
Initialize the
.Nm
container
.Fa ref
for use in the specified domain.
.It Fn specificdata_fini sd ref
Destroy the
.Nm
container
.Fa ref ,
and destroy all of the data values stuffed into the container.
.It Fn specificdata_getspecific "specificdata_domain_t sd" \
"specificdata_reference *ref" "specificdata_key_t key"
Retrieve the data value from the
.Nm
container
.Fa ref
associated with
.Fa key .
.It Fn specificdata_getspecific_unlocked sd ref key
Retrieve the data value from the
.Nm
container
.Fa ref
associated with
.Fa key
in a lockless manner.
Care must be taken to ensure that no other thread could cause
.Fa ref
to become invalid (i.e. point at the wrong container) by issuing a
.Fn setspecific
call or by destroying the container.
.It Fn specificdata_setspecific sd ref key data
Store the value
.Fa data
in the
.Nm
container
.Fa ref
and associate it with
.Fa key .
If a value has previously been set, the new value replaces the original
value.
.It Fn specificdata_setspecific_nowait sd ref key data
(Unimplemented)
.El
.Sh CODE REFERENCES
The 
.Nm
functionality is implemented in
.Pa sys/kern/subr_specificdata.c .
.Pp
The header file
.In sys/sys/specificdata.h
describes the public interface.
.Sh HISTORY
The
.Nm
subsystem first appeared in
.Nx 4.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
system was written by
.An Jason Thorpe Aq Mt thorpej@NetBSD.org .
This manual page was written by
.An Paul Goyette Aq Mt pgoyette@NetBSD.org .