[RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging

[Laura Abbott]

On 03/14/2017 07:47 AM, Benjamin Gaignard wrote:
> 2017-03-13 22:09 GMT+01:00 Laura Abbott <labbott at redhat.com>:
>> On 03/12/2017 12:05 PM, Daniel Vetter wrote:
>>> On Sun, Mar 12, 2017 at 2:34 PM, Benjamin Gaignard
>>> <benjamin.gaignard at linaro.org> wrote:
>>>> 2017-03-09 18:38 GMT+01:00 Laura Abbott <labbott at redhat.com>:
>>>>> On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
>>>>>> 2017-03-06 17:04 GMT+01:00 Daniel Vetter <daniel at ffwll.ch>:
>>>>>>> On Mon, Mar 06, 2017 at 11:58:05AM +0100, Mark Brown wrote:
>>>>>>>> On Mon, Mar 06, 2017 at 11:40:41AM +0100, Daniel Vetter wrote:
>>>>>>>>
>>>>>>>>> No one gave a thing about android in upstream, so Greg KH just dumped it
>>>>>>>>> all into staging/android/. We've discussed ION a bunch of times, recorded
>>>>>>>>> anything we'd like to fix in staging/android/TODO, and Laura's patch
>>>>>>>>> series here addresses a big chunk of that.
>>>>>>>>
>>>>>>>>> This is pretty much the same approach we (gpu folks) used to de-stage the
>>>>>>>>> syncpt stuff.
>>>>>>>>
>>>>>>>> Well, there's also the fact that quite a few people have issues with the
>>>>>>>> design (like Laurent).  It seems like a lot of them have either got more
>>>>>>>> comfortable with it over time, or at least not managed to come up with
>>>>>>>> any better ideas in the meantime.
>>>>>>>
>>>>>>> See the TODO, it has everything a really big group (look at the patch for
>>>>>>> the full Cc: list) figured needs to be improved at LPC 2015. We don't just
>>>>>>> merge stuff because merging stuff is fun :-)
>>>>>>>
>>>>>>> Laurent was even in that group ...
>>>>>>> -Daniel
>>>>>>
>>>>>> For me those patches are going in the right direction.
>>>>>>
>>>>>> I still have few questions:
>>>>>> - since alignment management has been remove from ion-core, should it
>>>>>> be also removed from ioctl structure ?
>>>>>
>>>>> Yes, I think I'm going to go with the suggestion to fixup the ABI
>>>>> so we don't need the compat layer and as part of that I'm also
>>>>> dropping the align argument.
>>>>>
>>>>>> - can you we ride off ion_handle (at least in userland) and only
>>>>>> export a dma-buf descriptor ?
>>>>>
>>>>> Yes, I think this is the right direction given we're breaking
>>>>> everything anyway. I was debating trying to keep the two but
>>>>> moving to only dma bufs is probably cleaner. The only reason
>>>>> I could see for keeping the handles is running out of file
>>>>> descriptors for dma-bufs but that seems unlikely.
>>>>>>
>>>>>> In the future how can we add new heaps ?
>>>>>> Some platforms have very specific memory allocation
>>>>>> requirements (just have a look in the number of gem custom allocator in drm)
>>>>>> Do you plan to add heap type/mask for each ?
>>>>>
>>>>> Yes, that was my thinking.
>>>>
>>>> My concern is about the policy to adding heaps, will you accept
>>>> "customs" heap per
>>>> platforms ? per devices ? or only generic ones ?
>>>> If you are too strict, we will have lot of out-of-tree heaps and if
>>>> you accept of of them
>>>> it will be a nightmare to maintain....
>>>
>>> I think ion should expose any heap that's also directly accessible to
>>> devices using dma_alloc(_coherent). That should leave very few things
>>> left, like your SMA heap.
>>>
>>>> Another point is how can we put secure rules (like selinux policy) on
>>>> heaps since all the allocations
>>>> go to the same device (/dev/ion) ? For example, until now, in Android
>>>> we have to give the same
>>>> access rights to all the process that use ION.
>>>> It will become problem when we will add secure heaps because we won't
>>>> be able to distinguish secure
>>>> processes to standard ones or set specific policy per heaps.
>>>> Maybe I'm wrong here but I have never see selinux policy checking an
>>>> ioctl field but if that
>>>> exist it could be a solution.
>>>
>>> Hm, we might want to expose all the heaps as individual
>>> /dev/ion_$heapname nodes? Should we do this from the start, since
>>> we're massively revamping the uapi anyway (imo not needed, current
>>> state seems to work too)?
>>> -Daniel
>>>
>>
>> I thought about that. One advantage with separate /dev/ion_$heap
> 
> Should we use /devi/ion/$heap instead of /dev/ion_$heap ?
> I think it would be easier for user to look into one directory rather
> then in whole /dev to find the heaps
> 

If we decide to move away from /dev/ion we can consider it.

>> is that we don't have to worry about a limit of 32 possible
>> heaps per system (32-bit heap id allocation field). But dealing
>> with an ioctl seems easier than names. Userspace might be less
>> likely to hardcode random id numbers vs. names as well.
> 
> In the futur I think that heap type will be replaced by a "get caps"
> ioctl which will
> describe heap capabilities. At least that is my understanding of kernel part
> of "unix memory allocator" project
> 

I don't think it will be completely replaced. A heap can have multiple
capabilities so I suspect there will need to be some cap -> allocation
instance translation. Of course all this is wild speculation since
much of the unix memory allocator isn't well defined yet.

Thanks,
Laura