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.\" $FreeBSD: head/share/man/man9/g_data.9 267936 2014-06-26 21:44:30Z bapt $
.\"
.Dd January 16, 2004
.Dt G_DATA 9
.Os
.Sh NAME
.Nm g_read_data ,
.Nm g_write_data
.Nd "read/write data from/to GEOM consumer"
.Sh SYNOPSIS
.In geom/geom.h
.Ft "void *"
.Fo g_read_data
.Fa "struct g_consumer *cp" "off_t offset" "off_t length" "int *error"
.Fc
.Ft int
.Fo g_write_data
.Fa "struct g_consumer *cp" "off_t offset" "void *ptr" "off_t length"
.Fc
.Sh DESCRIPTION
The
.Fn g_read_data
function reads
.Fa length
bytes of data from the provider attached to consumer
.Fa cp ,
starting at offset
.Fa offset .
The buffer returned from
.Fn g_read_data
is allocated with
.Fn g_malloc ,
so it should be freed by the caller with
.Fn g_free
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
function writes
.Fa length
bytes of data from the buffer pointed to by
.Fa ptr
to the provider attached to consumer
.Fa cp ,
starting at offset
.Fa offset .
.Sh RESTRICTIONS/CONDITIONS
The
.Fa length
argument
should be a multiple of the provider's sectorsize
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
The
.Fn g_read_data
function returns a pointer to a data buffer or
.Dv NULL
if an error occurred.
In that case an error value is stored in the
.Fa error
argument unless it is
.Dv NULL .
.Pp
The
.Fn g_write_data
function returns 0 if successful; otherwise an error code is returned.
.Sh ERRORS
Possible errors:
.Bl -tag -width Er
.It Bq Er EIO
An I/O error occurred while reading from or writing to the consumer.
.El
.Sh SEE ALSO
.Xr geom 4 ,
.Xr DECLARE_GEOM_CLASS 9 ,
.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 Mt pjd@FreeBSD.org .