config root man

.\" Author:	Juli Mallett <jmallett@FreeBSD.org>
.\" Date:	June 04, 2003
.\" Description:
.\" 	Manual page for libufs functions:
.\"		bread(3)
.\"		bwrite(3)
.\"
.\" This file is in the public domain.
.\"
.\" $FreeBSD: release/9.1.0/lib/libufs/bread.3 174668 2007-12-16 18:02:37Z phk $
.\"
.Dd June 4, 2003
.Dt BREAD 3
.Os
.Sh NAME
.Nm bread , bwrite
.Nd read and write blocks of a UFS file system
.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 ssize_t
.Fn bread "struct uufsd *disk" "ufs2_daddr_t blockno" "void *data" "size_t size"
.Ft ssize_t
.Fo bwrite
.Fa "struct uufsd *disk" "ufs2_daddr_t blockno"
.Fa "const void *data" "size_t size"
.Fc
.Ft int
.Fo berase
.Fa "struct uufsd *disk" "ufs2_daddr_t blockno" "ufs2_daddr_t size"
.Fc
.Sh DESCRIPTION
The
.Fn bread ,
.Fn bwrite
and
.Fn berase
functions provide a block read, write and erase API for
.Xr libufs 3
consumers.
They operate on a userland UFS disk structure, and perform the read
and write at a given block address, which uses the current
.Va d_bsize
value of the structure.
.Sh RETURN VALUES
The
.Fn bread
and
.Fn bwrite
functions return the amount read or written, or \-1 in case of any error,
including short read.
.Pp
The
.Fn berase
function returns non-zero on error.
.Sh ERRORS
The function
.Fn bread
may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr ufs_disk_write 3
or
.Xr pread 2 .
.Pp
The function
.Fn bwrite
may fail and set
.Va errno
for any of the errors specified for the library function
.Xr pwrite 2 .
.Pp
The function
.Fn berase
may fail and set
.Va errno
for any of the errors specified for the library function
.Xr ioctl 2 .
.Pp
Additionally all three functions may follow the
.Xr libufs 3
error methodologies in situations where the amount of data written
is not equal to the amount requested, or in case of a device error.
.Sh SEE ALSO
.Xr libufs 3 ,
.Xr ufs_disk_write 3
.Sh HISTORY
These functions first appeared as part of
.Xr libufs 3
in
.Fx 5.0 .
.Sh AUTHORS
.An Juli Mallett Aq jmallett@FreeBSD.org