linux-kernel - Re: [Linaro-mm-sig] [RFC][PATCH 0/6] ion: improved ABI

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Message-ID: <9871ed15-9188-410c-cac8-c5b887538c61@redhat.com>
Date:	Wed, 8 Jun 2016 10:29:05 -0700
From:	Laura Abbott <labbott@...hat.com>
To:	Chen Feng <puck.chen@...ilicon.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	John Stultz <john.stultz@...aro.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>
Cc:	devel@...verdev.osuosl.org, Jon Medhurst <tixy@...aro.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	linux-kernel@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	Jeremy Gebben <jgebben@...eaurora.org>,
	Eun Taik Lee <eun.taik.lee@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [Linaro-mm-sig] [RFC][PATCH 0/6] ion: improved ABI

On 06/06/2016 11:59 PM, Chen Feng wrote:
> The idea is good, define the heap ids in header file is inconvenient.
>
> But if we query the heaps information from user-space.
>
> It need to maintain this ids and name userspace one by one. The code may
> be complicated in different module user-space.
>
> In android, the gralloc and other lib will all use ion to alloc memory.
>
> This will make it more difficult to maintain user-space code.
>

This was a concern I had had as well. Anything that involves dynamic
probing is going to involve more tracking. Do you think some library
code in libion would help?

Thanks,
Laura

>
> But beyond this, The new alloc2 with not-handle flag is good.
> And the pull out of ioctl interface is also a good cleanup.
>
> On 2016/6/7 2:23, Laura Abbott wrote:
>>
>> The ABI for Ion's ioctl interface are a pain to work with. The heap IDs
>> are a 32-bit non-discoverable namespace that form part of the ABI. There's
>> no way to determine what ABI version is in use which leads to problems
>> if the ABI changes or needs to be updated.
>>
>> This series is a first approach to give a better ABI for Ion. This includes:
>>
>> - Following the advice in botching-up-ioctls.txt
>> - Ioctl for ABI version
>> - Dynamic assignment of heap ids
>> - queryable heap ids
>> - Runtime mapping of heap ids, including fallbacks. This avoids the need to
>>   encode the fallbacks as an ABI.
>>
>> I'm most interested in feedback if this ABI is actually an improvement and
>> usable. The heap id map/query interface seems error prone but I didn't have
>> a cleaner solution. There aren't any kernel APIs for the new features as the
>> focus was on a userspace API but I anticipate that following easily once
>> the userspace API is established.
>>
>>
>> Thanks,
>> Laura
>>
>> P.S. Not to turn this into a bike shedding session but if you have suggestions
>> for a name for this framework other than Ion I would be interested to hear
>> them. Too many other things are already named Ion.
>>
>> Laura Abbott (6):
>>   staging: android: ion: return error value for ion_device_add_heap
>>   staging: android: ion: Switch to using an idr to manage heaps
>>   staging: android: ion: Drop heap type masks
>>   staging: android: ion: Pull out ion ioctls to a separate file
>>   staging: android: ion: Add an ioctl for ABI checking
>>   staging: android: ion: Introduce new ioctls for dynamic heaps
>>
>>  drivers/staging/android/ion/Makefile    |   3 +-
>>  drivers/staging/android/ion/ion-ioctl.c | 243 ++++++++++++++++++
>>  drivers/staging/android/ion/ion.c       | 438 ++++++++++++++++----------------
>>  drivers/staging/android/ion/ion_priv.h  | 109 +++++++-
>>  drivers/staging/android/uapi/ion.h      | 164 +++++++++++-
>>  5 files changed, 728 insertions(+), 229 deletions(-)
>>  create mode 100644 drivers/staging/android/ion/ion-ioctl.c
>>
>