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.\"	$NetBSD: disklabel.9,v 1.13 2008/04/30 13:10:58 martin Exp $
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" by Paul Kranenburg.
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.Dd December 26, 1996
.Dt DISKLABEL 9
.Os
.Sh NAME
.Nm disklabel ,
.Nm readdisklabel ,
.Nm writedisklabel ,
.Nm setdisklabel ,
.Nm bounds_check_with_label
.Nd disk label management routines
.Sh SYNOPSIS
.Ft char *
.Fn readdisklabel "dev_t dev" "void (*strat)(struct buf *)" "struct disklabel *lp" "struct cpu_disklabel *clp"
.Ft int
.Fn writedisklabel "dev_t dev" "void (*strat)(struct buf *)" "struct disklabel *lp" "struct cpu_disklabel *clp"
.Ft int
.Fn setdisklabel "struct disklabel *olp" "struct disklabel *nlp" "u_long openmask" "struct cpu_disklabel *clp"
.Ft int
.Fn bounds_check_with_label "struct buf *bp" "struct disklabel *lp" "int wlabel"
.Sh DESCRIPTION
This collection of routines provides a disklabel management interface to
kernel device drivers.
These routines are classified as machine- or architecture-dependent because
of restrictions imposed by the machine architecture and boot-strapping code
on the location of the label, or because cooperation with other operating
systems requires specialized conversion code.
.Pp
.Fn readdisklabel
attempts to read a disklabel from the device identified by
.Fa dev ,
using the device strategy routine passed in
.Fa strat .
Note that a buffer structure is required to pass to the strategy routine;
it needs to be acquired and parameterized for the intended I/O operation,
and disposed of when the operation has completed.
Some fields in the disklabel passed in
.Fa lp
may be pre-initialized by the caller in order to meet device driver
requirements for the I/O operation initiated to get to the disklabel data
on the medium.
In particular, the field
.Dq d_secsize ,
if non-zero, is used by
.Fn readdisklabel
to get an appropriately sized buffer to pass to the device strategy routine.
Unspecified fields in
.Fa lp
should be set to zero.
If the medium does not contain a native disklabel that can be read in directly,
.Fn readdisklabel
may resort to constructing a label from other machine-dependent information
using the provided buffer passed in the
.Fa clp
argument.
If a disk label can not be found or constructed, a string containing
an approximated description of the failure mode is returned.
Otherwise the
.Dv NULL
string is returned.
.Pp
.Fn writedisklabel
stores disk label information contained in the disk label structure given by
.Fa lp
on the device identified by
.Fa dev .
Like
.Fn readdisklabel ,
it acquires and sets up an I/O buffer to pass to the strategy routine
.Fa strat .
.Fn writedisklabel
may elect to do a machine-dependent conversion of the native disk label
structure
.Po
using the buffer pointed at by
.Fa clp
.Pc ,
to store the disk label onto the medium in a format complying with
architectural constraints.
.Fn writedisklabel
returns 0 on success and
.Dv EINVAL
if the disk label specifies invalid or inconvertible values.
Otherwise, any error condition reported by the device strategy routine
in the buffer's
.Dq Va b_error
field is returned.
.Pp
.Fn setdisklabel
checks a proposed new disk label passed in
.Fa nlp
for some amount of basic sanity.
This includes a check on attempts to
change the location, or reduce the size, of an existing disk partition
that is currently in use by the system.
The current disposition of the disk partitions is made available through
.Fa olp
and
.Fa openmask ,
which provide, respectively, the existing disk label and a bit mask
identifying the partitions that are currently in use.
Failure to pass on
.Dq basic sanity ,
results in a
.Dv EINVAL
return value, while a vetoed update of the partition layout is signaled by a
.Dv EBUSY
return value.
Otherwise, 0 is returned.
.Pp
.Fn bounds_check_with_label
is used to check whether a device transfer described by
.Fa bp
to the device identified by
.Fa dev ,
is properly contained within a disk partition of the disk with label
.Fa lp .
If this check fails,
.Fn bounds_check_with_label
sets the buffer's
.Dq Va b_error
field to
.Dv EINVAL ,
sets the
.Dv B_ERROR
flag in
.Dq Va b_flags ,
and returns -1.
If the argument
.Fa wlabel
is zero, and the transfer is a write operation, a check is done if the transfer
would overwrite
.Pq a portion of
the disklabel area on the medium.
If that is the case,
.Dv EROFS
is set in
.Dq Va b_error ,
the
.Dv B_ERROR
flag is set in
.Dq Va b_flags ,
and -1 is returned.
Note that
.Fa wlabel
should be set to a non-zero value if the intended operation is expected to
install or update the disk label.
Programs that intend to do so using the raw device interface should notify
the driver by using a
.Dv DIOCWLABEL
ioctl function.
.Sh SEE ALSO
.Xr disklabel 5 ,
.Xr disklabel 8