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.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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.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_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 .