If I create a partition that is one cylinder in length, parted fails
with its gratuitous "Unable to satisfy all constraints on the partition"
error.  Presumably this is an off-by-one problem?

The alpha port of debian-installer needs to be able to reserve a minimal
amount of disk space at the front of the boot disk for a bootloader,
which means partman must be able to handle partitions of this size.
Even a one-cylinder partition leaves a lot of space unused, so a
two-cylinder partition is vast overkill.

Ok, correction: the problem actually seems to be that parted can't
handle partitions that start at sector 0, but this is precisely where
one would expect the partition to start on a BSD disklabel.

After changing the constraint to use 0 as a start point instead of 1,
parted then complains that this overlaps with the metadata
(partition # -1), which has a start and end of 0.  Considering my boot
disk appears to have sectors of 32 bytes, and the offset of the actual
disk label is 64 bytes, it doesn't seem to make much sense to regard
this as an overlap.

However, since I now know I can route around this bit of funkiness by
starting my boot partition on sector 1 instead of sector 0 (where fdisk
will put it by default), I'll see if I can't come up with a workable
solution for d-i this way.

Thanks,

Well, this is a MBR based partition table, isn't it ? the metadata is
the sector who contains the partition table, and you can't put a
partition table there, obviously.

Friendly,

Sven Luther

In this particular case, the partition I'm creating is a dummy
partition, to reserve a small amount of space for aboot.  This is on an
alpha, using BSD disklabels; it certainly doesn't have the concept of an
MBR here, and even though I am overlapping the actual disklabel, this
doesn't matter since the bootloader config tools know how to handle
disklabels on their own.

In general, parted is much less forgiving of disklabels than the rest of
the world -- on Tru64, in fact, it's quite common to have a partition
configured as "whole disk", i.e., overlapping all other partitions.  Of
course, the Alpha bootloader installer can't handle such a configuration
either, so this is of minor consequence.

Yeah, a BSD then, still the BSD disk label is marked as metadata, and
you can't reuse it. I am not entirely sure what to do here, do you have
some suggestion ? Can you also tell me exactly how do you want to set
the aboot space in the cylinder containing also the partition table ?
The layout of it i mean.

Also, maybe it would be a good idea to not 'hide' the metadata partition
like it is done now, but i doubt this would be a easy fix.

Friendly,

Sven Luther

Well, for creating new partitions in d-i, we should be ok; this
partition's only purpose in life is to prevent *other* partitions from
being created at the front of the disk, so if there's a space at the
front that is already protected by parted itself, this is perfectly ok.

So this bug only affects the fact that d-i can't read existing BSD
disklabels on systems that may have had other OSes installed on them,
OSes that do allow things like partitions that overlap the disklabel.
I'm not sure how big a problem this is; it probably warrants keeping
this report open, IMHO, but downgrading it from "important".