Added first part of GEOM kernel API manuals pages.

Documented function and macros are:
	- DECLARE_GEOM_CLASS(),
	- g_attach(),
	- g_detach(),
	- g_new_bio(),
	- g_clone_bio(),
	- g_destroy_bio(),
	- g_new_consumer(),
	- g_destroy_consumer(),
	- g_read_data(),
	- g_write_data(),
	- g_post_event(),
	- g_waitfor_event(),
	- g_cancel_event(),
	- g_new_geomf(),
	- g_destroy_geom(),
	- g_new_providerf(),
	- g_destroy_provider(),
	- g_error_provider(),
	- g_provider_by_name(),
	- g_wither_geom().
and more to come.

I want to thanks following people for help with those documents:
	Slawek Zak <zaks@prioris.mini.pw.edu.pl>
	Simon L. Nielsen <simon@FreeBSD.org>
	Pieter de Boer <g.p.de.boer@st.hanze.nl>
and of course
	Poul-Henning Kamp <phk@FreeBSD.org>

Reviewed by:	phk, scottl
Approved by:	phk, scottl (mentor)

1 files changed, 224 insertions, 0 deletions

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+.\"
+.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd January 16, 2004
+.Dt g_bio 9
+.Os
+.Sh NAME
+.Nm g_new_bio ,
+.Nm g_clone_bio ,
+.Nm g_destroy_bio
+.Nd "bio controlling functions"
+.Sh SYNOPSIS
+.In sys/bio.h
+.In geom/geom.h
+.Ft "struct bio *"
+.Fn g_new_bio void
+.Ft "struct bio *"
+.Fn g_clone_bio "struct bio *bp"
+.Ft void
+.Fn g_destroy_bio "struct bio *bp"
+.Sh DESCRIPTION
+The
+.Fa bio
+structure is used by GEOM to describe I/O requests.
+Most important fields of
+.Fa struct bio
+are described below:
+.Bl -tag -width ".Va bio_attribute"
+.It Va bio_cmd
+I/O request number.
+There are four I/O requests available in GEOM:
+.Bl -tag -width BIO_GETATTR
+.It Dv BIO_READ
+Self explanatory.
+.It Dv BIO_WRITE
+Self explanatory.
+.It Dv BIO_DELETE
+Delete indicates that a certain range of data is no longer used and that
+it can be erased or freed as the underlying technology supports.
+Technologies like flash adaptation layers can arrange to erase the relevant
+blocks before they will become reassigned and cryptographic devices may
+want to fill random bits into the range to reduce the amount of data
+available for attack.
+.It Dv BIO_GETATTR
+Get attribute supports inspection and manipulation of out\-of\-band
+attributes on a particular provider or path.
+Attributes are named by ascii strings and are stored in the
+.Va bio_attribute
+field.
+.El
+.It Va bio_offset
+Offset into provider.
+.It Va bio_data
+Pointer to data buffer.
+.It Va bio_flags
+Available flags:
+.Bl -tag -width BIO_GETATTR
+.It Dv BIO_ERROR
+Request failed (error value is stored in
+.Va bio_error )
+field.
+.It Dv BIO_DONE
+Request finished.
+.It Dv BIO_FLAG1
+Avaliable for private use.
+.It Dv BIO_FLAG2
+Avaliable for private use.
+.El
+.It Va bio_error
+Error value when BIO_ERROR is set.
+.It Va bio_done
+Pointer to function which will be called on request finish.
+.It Va bio_driver1
+Private use by the callee (ie: the provider).
+.It Va bio_driver2
+Private use by the callee (ie: the provider).
+.It Va bio_caller1
+Private use by the caller (ie: the consumer).
+.It Va bio_caller2
+Private use by the caller (ie: the consumer).
+.It Va bio_attribute
+Attribute string for BIO_GETATTR request.
+.It Va bio_from
+Consumer to use for request (attached to provider stored in
+.Va bio_to
+field) (typically read\-only for a class).
+.It Va bio_to
+Destination provider (typically read\-only for a class).
+.It Va bio_length
+Request length in bytes.
+.It Va bio_completed
+Number of bytes completed, but they may not be completed from
+the front of the request.
+.It Va bio_children
+Number of bio clones (typically read\-only for a class).
+.It Va bio_inbed
+Number of finished bio clones.
+.It Va bio_parent
+Pointer to parent bio.
+.El
+.Pp
+The
+.Fn g_new_bio
+function allocates a new, empty
+.Vt bio
+structure.
+.Pp
+The
+.Fn g_clone_bio
+function allocates a new
+.Vt bio
+structure and copies those fields from the
+.Vt bio
+structure given as an argument to clone:
+.Va bio_cmd ,
+.Va bio_length ,
+.Va bio_offset ,
+.Va bio_data ,
+.Va bio_attribute .
+The field
+.Va bio_parent
+in clone is set to source
+.Vt bio
+and the field
+.Va bio_children
+in parent is increased.
+.Pp
+This function should be used for every request which enters through
+the provider of a particular geom and needs to be scheduled down.
+Proper order is:
+.Pp
+.Bl -enum -compact
+.It
+Clone
+.Vt "struct bio" .
+.It
+Modify the clone.
+.It
+Schedule the clone on its own consumer.
+.El
+.Pp
+The
+.Fn g_destroy_bio
+function kills the given
+.Vt bio
+structure.
+.Sh EXAMPLES
+Implementation of
+.Dq Dv NULL Ns \-transformation ,
+meaning that an I/O request is cloned and scheduled down without any
+modifications.
+Let's assume that field
+.Va ex_consumer
+in structure
+.Vt example_softc
+contains a consumer attached to the provider we want to operate on.
+.Bd -literal -offset indent
+void
+example_start(struct bio *bp)
+{
+	struct example_softc *sc;
+	struct bio *cbp;
+
+	sc = bp->bio_to->geom->softc;
+	if (sc == NULL) {
+		g_io_deliver(bp, ENXIO);
+		return;
+	}
+
+	/* Let's clone our bio request. */
+	cbp = g_clone_bio(bp);
+	if (cbp == NULL) {
+		g_io_deliver(bp, ENOMEM);
+		return;
+	}
+	cbp->bio_done = g_std_done;	/* Standard 'done' function. */
+
+	/* Ok, schedule it down. */
+	/*
+	 * The consumer can be obtained from
+	 * LIST_FIRST(&bp->bio_to->geom->consumers) as well,
+	 * if there is only one in our geom.
+	 */
+	g_io_request(cbp, sc->ex_consumer);
+}
+.Ed
+.Sh SEE ALSO
+.Xr DECLARE_GEOM_CLASS 9 ,
+.Xr geom 4 ,
+.Xr g_attach 9 ,
+.Xr g_consumer 9 ,
+.Xr g_data 9 ,
+.Xr g_event 9 ,
+.Xr g_geom 9 ,
+.Xr g_provider 9 ,
+.Xr g_provider_by_name 9 ,
+.Xr g_wither_geom 9
+.Sh AUTHORS
+.An -nosplit
+This manual page was written by
+.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .