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.\" Author:	Juli Mallett <jmallett@FreeBSD.org>
.\" Date:	June 04, 2003
.\" Description:
.\" 	Manual page for libufs functions:
.\"		cgread(3)
.\"		cgread1(3)
.\"		cgwrite1(3)
.\"
.\" This file is in the public domain.
.\"
.\" $FreeBSD: release/9.1.0/lib/libufs/cgread.3 163835 2006-10-31 21:21:48Z pjd $
.\"
.Dd June 4, 2003
.Dt CGREAD 3
.Os
.Sh NAME
.Nm cgread , cgread1, cgwrite1
.Nd read/write cylinder groups of UFS disks
.Sh LIBRARY
.Lb libufs
.Sh SYNOPSIS
.In sys/param.h
.In sys/mount.h
.In ufs/ufs/ufsmount.h
.In ufs/ufs/dinode.h
.In ufs/ffs/fs.h
.In libufs.h
.Ft int
.Fn cgread "struct uufsd *disk"
.Ft int
.Fn cgread1 "struct uufsd *disk" "int c"
.Ft int
.Fn cgwrite1 "struct uufsd *disk" "int c"
.Sh DESCRIPTION
The
.Fn cgread
and
.Fn cgread1
functions provide cylinder group reads for
.Xr libufs 3
consumers.
The
.Fn cgread1
function reads from one cylinder group, specified by
.Fa c
into the
.Va d_cg
field of a userland UFS disk structure.
It sets the
.Va d_lcg
field to the cylinder group number
.Fa c .
.Pp
The
.Fn cgread
function operates on sequential cylinder groups.
Calling the
.Fn cgread
function is equivalent to calling
.Fn cgread1
with a cylinder group specifier equivalent to the value of the current
.Va d_ccg
field, and then incrementing the
.Va d_ccg
field.
.Pp
The
.Fn cgwrite1
function stores cylinder group specified by
.Fa c
from
.Va d_cg
field of a userland UFS disk structure on disk.
.Sh RETURN VALUES
Both functions return 0 if there are no more cylinder groups to read,
1 if there are more cylinder groups, and \-1 on error.
.Sh ERRORS
The function
.Fn cgread
may fail and set
.Va errno
for any of the errors specified for the library function
.Xr bread 3 .
.Pp
The function
.Fn cgread1
has semantically identical failure conditions to those of
.Fn cgread .
.Pp
The function
.Fn cgwrite1
may fail and set
.Va errno
for any of the errors specified for the library function
.Xr bwrite 3 .
.Sh SEE ALSO
.Xr bread 3 ,
.Xr bwrite 3 ,
.Xr libufs 3
.Sh HISTORY
These functions first appeared as part of
.Xr libufs 3
in
.Fx 5.1 .
.Sh AUTHORS
.An Juli Mallett Aq jmallett@FreeBSD.org