.\"
.\" 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_data 9
.Os
.Sh NAME
.Nm g_read_data ,
.Nm g_write_data
.Nd "read/write data through consumer"
.Sh SYNOPSIS
.In geom/geom.h
.Ft "void *"
.Fn g_read_data "struct g_consumer *cp" "off_t offset" "off_t length" "int *error"
.Ft int
.Fn g_write_data "struct g_consumer *cp" "off_t offset" "void *ptr" "off_t length"
.Sh DESCRIPTION
The
.Fn g_read_data
reads
.Fa length
bytes of data from a provider through attached consumer
.Fa cp
starting at offset
.Fa offset .
Memory for data is allocated inside
.Fn g_read_data
with
.Fn g_malloc ,
and should therefor be freed by the caller with the
.Fn g_free
function after use.
If the operation fails, an error value will be stored in the
.Fa error
argument if it is not
.Dv NULL .
.Pp
The
.Fn g_write_data
writes
.Fa length
bytes of data from address
.Fa ptr
starting at offset
.Fa offset
to a provider through the attached consumer
.Fa cp .
.Sh RESTRICTIONS/CONDITIONS
Length of data should be a multiple of the sectorsize for the provider
and less than or equal to
.Dv DFLTPHYS
.Dv ( DFLTPHYS is defined in
.In sys/param.h ) .
.Pp
The topology lock must not be held.
.Sh RETURN VALUES
.Fn g_read_data
returns a pointer to the read data or
.Dv NULL
if an error occured.
In that case an error value is stored in the
.Fa error
argument unsless it is
.Dv NULL .
.Pp
.Fn g_write_data
returns the value 0 if successful; otherwise an error code is returned.
.Sh ERRORS
Possible errors:
.Bl -tag -width Er
.It Bq Er EIO
Can not read data.
.El
.Sh SEE ALSO
.Xr DECLARE_GEOM_CLASS 9 ,
.Xr geom 4 ,
.Xr g_access 9 ,
.Xr g_attach 9 ,
.Xr g_bio 9 ,
.Xr g_consumer 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 .