[udisks] Extended Partitions

[Georg Grabler]

Hi David,

Thanks for your answer, we'll take a look at UDisks2. Good to know that
there is work going on on UDisks2 (didn't know it was started), since there
is probably still room for some enhancements (not sure about feature freeze
for you and similar though).

For the 2nd problem with EPT, let's take a usual EPT partition layout
Primary Partition
EPT
Extended Partition 1
Extended Partition 2
Primary Partition
...

The disk setup will look something like this after creating the partitions
(the way we'd show it in the partitioning frontend):
Primary Partition
EPT
Extended Partition 1
Extended Partition 2
*<unallocated space>*
Parimary Partition/EPT/what ever

Now, the unallocated space in between the EPT and the primary partition is
there. I don't know why it is there, but in the specification of MSDOS
somewhere on my research I found that there can be a space between that due
to the reason the partition after the EPT needs to start at the next sector
of the disk, and thus cannot start immediately after the EPT. But this space
is not usable for partitioning, what's the reason we'd like to hide it, but
have no clue about the size of the disk sector(s), and therefore no clue
about if this should be shown or not.

I added the member of our team doing most work in this area now (shainer) to
the cc list. If this does not clarify the situation yet, I'm sure we can set
up some date to talk about it or shainer can probably explain it better than
I do ;-). I'll be around doing some more research this weekend as well
(always busy during weeks :-().

@PartEntryContainer:
That would indeed be nice indeed (and if it's for UDisks2), just for the
reason we would not have to care about different implementations in
different PTs - and leave the backend stuff to the thing which does all the
other disk magic for us, namely UDisks ;-).

@shainer: If I've gotten anything wrong in this mail, correct me please!
Thanks :-).

Kind regards,
Georg

On Thu, Sep 29, 2011 at 3:55 PM, David Zeuthen <zeuthen at gmail.com> wrote:

> Hi,
>
> On Fri, Sep 23, 2011 at 6:39 AM, Georg Grabler <ggrabler at gmail.com> wrote:
> > Dear UDisks Developers / Community.
> > To introduce me and us, I'm on the Chakra-Project team, mainly working on
> > the system installer Tribe. We are about to rewrite our whole
> partitioning
> > to UDisks (using the DBus interface), and are currently in the stage
> after
> > the dbus function implementation starting writing the user interface.
>
> You should probably be targeting udisks2 which is now on the master
> branch. It is expected to be done in a couple of months (targeting
> Fedora 17). I just uploaded a snapshot of the latest docs here
>
> http://people.freedesktop.org/~david/udisks2-20110929/
>
> > We're doing pretty well with that, but we're stuck with a problem now:
> > Extended partitions.
> >
> > The most serious problem we encounter is that after an EPT, the "next"
> > partition after the EPT usually has an offset which is the end of the
> > extended partition size to the next sector - as I understand the
> > specification. Having this in UDisks, we currently show "unallocated"
> space,
> > since there is an offset, and everything we don't know is "unallocated"
> to
> > us. Is there any way to check wether this unallocated space is "usable"
> or
> > "unusable" as in this case?
>
> I'm not entirely sure what this means.
>
> > The other thing isn't really critical as I see it, it's about the
> > PartitionType. We can check the value for 0x05 of 0x0F in the
> PartitionType
> > property to know if it's an EPT, though, I think there should be an
> easier
> > way than that to know if something is an "extended" partition or not
> (maybe
> > IdUsage, if it returns PartitionTable for EPT, just realized I didn't
> check
> > that before).
>
> We could add a properties PartEntryContainer (TRUE iff it's an
> extended partition) and PartEntryContainee (/ or objpath of the
> extended partition the partititon is part of).
>
> Thanks,
> David
>
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