Re: [RFC] Separating out libata out of SCSI (finally)

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2008-06-24 at 11:30 +0300, Boaz Harrosh wrote:
> James Bottomley wrote:
> > On Mon, 2008-06-23 at 17:04 -0400, Greg Freemyer wrote:
> >> I've seen a lot of end user complaints about libata only supporting
> >> 15(14?) partitions.  Will that limit be moved back to the traditional
> >> drivers/ide limit as part of this?
> > 
> > Number of partitions is directly related to number of minors, so it
> > can't be changed without a change in the allocation of major/minor space
> > in sd ... that could only be done compatibly by permuting the space.
> > The only other way to do it is incompatibly by changing major (again).
> > 
> Could we do both? I mean use the legacy, up to 15, with the old major,
> then use the new major for bigger then 15. Since user mode that knows
> about more then 15 partitions is new, it'll know it needs to jump a major.

Not simultaneously, which is the problem; you can't have two separate
block devices for the same physical device unless you want aliasing
issues in the page cache.

It might be possible to add an extra device to give access to the
missing partitions, but that would require a bit of re-engineering in
gendisk (which is the in-kernel code to manage the partitions).

What might be far more feasible is to set up udev to use kpartx to
provide the missing partitions if it detects a partition table that has
them ... of course, that requires a udev setup and most of the
complaints about the lost partitions seem to come from non-udev systems.

But .... if everyone (particularly the people with these problems) had
udev, we could simply migrate to a new major with more partitions, get
udev to fix it all up for us and everyone would be happy because no-one
would even notice that we'd moved majors ...

James