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.Dd September 1, 2019
.Dt EDAHDI 1 atari
.Os
.Sh NAME
.Nm edahdi
.Nd modify AHDI partition identifiers
.Sh SYNOPSIS
.Nm
.Ar device
.Sh DESCRIPTION
.Nm
allows you to modify the partition identifiers on a disk partitioned with
AHDI or an AHDI compatible formatter.
An AHDI partition format is usually only present on disks shared between
.Nx
and some other OS.
The partition identifiers are used by
.Nx
as a guideline to emulate a disklabel on such a disk.
.Pp
.Nm
supports the following options:
.Bl -tag -width device
.It Ar device
The name of the raw device you want to edit.
.El
.Pp
The following partition identifiers are recognized by
.Nx :
.Bl -tag -width "GEM or BGM" -compact
.It NBD
Partition is reserved for
.Nx .
This can be either a root or an user partition.
The first NBD partition on a disk will be mapped to partition
.Em a
in
.Nx .
The following NBD partitions will be mapped from
.Em d
up.
The filesystem type is ffs by default.
.It SWP
The first SWP partition is mapped to partition
.Em b .
.It GEM or BGM
These partitions are mapped from
.Em d
up.
The filesystem type is msdos.
.It NBR
.Nx
root partition (deprecated).
.It NBU
.Nx
user partition (deprecated).
.It NBS
.Nx
swap partition (deprecated).
.El
.Sh EXAMPLES
Say, you have a disk that is partitioned like:
.Bl -column Number   Id
.It Sy "Number" Ta Sy "Id"
.It 1 Ta GEM
.It 2 Ta GEM
.It 3 Ta GEM
.It 4 Ta GEM
.El
.Pp
This partitioning will show up in
.Nx
as (Number refers to the first table):
.Bl -column "c (whole disk)" "Fstype" "Number"
.It Sy Partition Ta Sy Fstype Ta Sy Number
.It c (whole disk) Ta unused Ta ""
.It d (user part) Ta MSDOS Ta 1
.It e (user part) Ta MSDOS Ta 2
.It f (user part) Ta MSDOS Ta 3
.It g (user part) Ta MSDOS Ta 4
.El
.Pp
Now you decide to change the id of partition 2 and 3 to NBD.
Now
.Nx
will show the partitioning as (Number refers to the first table):
.Bl -column "c (whole disk)" "Fstype" "Number"
.It Sy Partition Ta Sy Fstype Ta Sy Number
.It a (root) Ta 4.2BSD Ta 2
.It c (whole disk) Ta unused Ta ""
.It d (user part)  Ta MSDOS  Ta 1
.It e (user part)  Ta 4.2BSD Ta 3
.It f (user part)  Ta MSDOS  Ta 4
.El
.Pp
You will notice that the order of the partitions has changed! You will have
to watchout for this.
It is a consequence of
.Nx
habit of assigning a predefined meaning to the partitions
.Em a/b
and
.Em c .
.Sh SEE ALSO
.Xr disklabel 8 ,
.Xr installboot 8
.Sh HISTORY
The
.Nm
command first appeared in
.Nx 1.2 .
.Sh BUGS
The changes made to the AHDI partitions will become active on the next
.Em first open
of the device.
You are advised to use
.Nm
only on a device without any mounted or otherwise active partitions.
This is not enforced by
.Nm .
This is particularly confusing when your change caused partitions to shift,
as shown in the example above.
.Pp
As soon as a disk contains at least one NBD partition, you are allowed to
write disklabels and install bootstraps.