Re: staging: ion: ION allocation fall back order depends on heap linkage order

[Laura Abbott]

On 02/06/2018 11:05 PM, Alexey Skidanov wrote:
> > Yup, you've hit upon a key problem. Having fallbacks be stable
> > was always a problem and the recommendation these days is to
> > not rely on them. You can specify a heap at a time and fallback
> > manually if you want that behavior.
> >
> > If you have a proposal to make fallbacks work reliably without
> > overly complicating the ABI I'm happy to review it.
> >
> > Thanks,
> > Laura
> I think it's possible to "automate" the "manual fallback" behavior. But
> the real issues is using heap id to specify the particular heap object.
>
> Current API (allocation IOCTL) requires to specify the particular heap
> object by using heap id. From the other hand, the user space doesn't
> control the heaps creation order and heap id assignment. So it may be
> tricky, especially when more than one object of the same heap type is
> created automatically.
>
> Thanks,
> Alexey

The query ioctl is designed to get the heap ID information without
needing to rely on the linking order or anything else defined in
the kernel.

Thanks,
Laura