On Fri, Feb 15, 2019 at 2:51 AM Brian Starkey <brian.star...@arm.com> wrote: > > 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.
Potentially, though that implicitly still caps the heaps to 32. So I'm not sure what the net benefit would be. > > 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. Yea I think having a proper ION_IOC_VERSION is going to be necessary. I'm hoping to send out an ugly first stab at the kernel side for switching to per-heap devices (with a config for keeping /dev/ion for legacy compat), which I hope will address the core issue this patch does (moving away from heap masks to specifically requested heaps). thanks -john _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
