Re: [PATCHv2 4/4] staging: android: ion: Add ioctl to query available heaps

[Laura Abbott <labbott@redhat.com>]

On 09/01/2016 04:44 PM, kbuild test robot wrote:
> Hi Laura,
>
> [auto build test WARNING on next-20160825]
> [cannot apply to staging/staging-testing v4.8-rc4 v4.8-rc3 v4.8-rc2 v4.8-rc4]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> [Suggest to use git(>=2.9.0) format-patch --base=<commit> (or --base=auto for convenience) to record what (public, well-known) commit your patch series was built on]
> [Check https://git-scm.com/docs/git-format-patch for more information]
>
> url:    https://github.com/0day-ci/linux/commits/Laura-Abbott/staging-android-ion-Drop-heap-type-masks/20160902-071022
> config: mips-allyesconfig (attached as .config)
> compiler: mips-linux-gnu-gcc (Debian 5.4.0-6) 5.4.0 20160609
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=mips
>
> All warnings (new ones prefixed by >>):
>
>    drivers/staging/android/ion/ion.c: In function 'ion_query_heaps':
>>> drivers/staging/android/ion/ion.c:1181:3: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>       (struct ion_heap_data __user *)query->heaps;
>       ^
>

botching-up-ioctls.txt says:

  * Pointers are __u64, cast from/to a uintprt_t on the userspace side and
    from/to a void __user * in the kernel. Try really hard not to delay this
    conversion or worse, fiddle the raw __u64 through your code since that
    diminishes the checking tools like sparse can provide.

This doesn't seem like it will work on 32-bit systems since you'll end up
with the warning above. Is there a better option or did I misunderstand
how that is supposed to work?

Thanks,
Laura