Messages in this thread | | | From | Brian Starkey <> | Subject | Re: [PATCH v2] staging: android: ion: Allocate from heap ID directly without mask | Date | Fri, 15 Feb 2019 10:50:58 +0000 |
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Hi John,
On Thu, Feb 14, 2019 at 09:38:29AM -0800, John Stultz wrote: > [snip]
> Some thoughts, as this ABI break has the potential to be pretty painful. > > 1) Unfortunately, this ABI is exposed *through* libion via > ion_alloc/ion_alloc_fd out to gralloc implementations. Which means it > will have a wider impact to vendor userland code.
I figured libion could fairly easily loop through all the set bits in heap_mask and call the ioctl for each until it succeeds. That preserves the old behaviour from the libion clients' perspective.
> > 2) For patches that cause ABI breaks, it might be good to make it > clear in the commit what the userland impact looks like in userspace, > possibly with an example, so the poor folks who bisect down the change > as breaking their system in a year or so have a clear example as to > what they need to change in their code. > > 3) Also, its not clear how a given userland should distinguish between > the different ABIs. We already have logic in libion to distinguish > between pre-4.12 legacy and post-4.12 implementations (using implicit > ion_free() behavior). I don't see any such check we can make with this > code. Adding another ABI version may require we provide an actual > interface version ioctl. >
A slightly fragile/ugly approach might be to attempt a small allocation with a heap_mask of 0xffffffff. On an "old" implementation, you'd expect that to succeed, whereas it would/could be made to fail in the "new" one.
Thanks, -Brian
> > thanks > -john
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