Op 03-02-16 om 21:09 schreef Gustavo Padovan:
> Hi Maarten,
>
> 2016-02-03 Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>:
>
>> Op 03-02-16 om 14:25 schreef Gustavo Padovan:
>>> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
>>>
>>> Turn sync_fence_info into __u64 type enable us to extend the struct in the
>>> future without breaking the ABI.
>>>
>>> v2: use type __u64 for fence_info
>>>
>>> v3: fix commit message to reflect the v2 change
>>>
>>> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
>>> ---
>>> drivers/staging/android/sync.c | 2 +-
>>> drivers/staging/android/uapi/sync.h | 2 +-
>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
>>> index 2ab0c20..8425457 100644
>>> --- a/drivers/staging/android/sync.c
>>> +++ b/drivers/staging/android/sync.c
>>> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>>> if (info->status >= 0)
>>> info->status = !info->status;
>>>
>>> - len = sizeof(struct sync_file_info);
>>> + len = sizeof(struct sync_file_info) - sizeof(__u64);
>>>
>>> for (i = 0; i < sync_file->num_fences; ++i) {
>>> struct fence *fence = sync_file->cbs[i].fence;
>>> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
>>> index a0cf357..e649953 100644
>>> --- a/drivers/staging/android/uapi/sync.h
>>> +++ b/drivers/staging/android/uapi/sync.h
>>> @@ -54,7 +54,7 @@ struct sync_file_info {
>>> char name[32];
>>> __s32 status;
>>>
>>> - __u8 sync_fence_info[0];
>>> + __u64 sync_fence_info;
>>> };
>>>
>>> #define SYNC_IOC_MAGIC '>'
>> This still doesn't do what you expect it to.
>>
>> I think this is what you want is for userspace to do:
>>
>> struct sync_file_info info;
>>
>> info.flags = info.num_fences = 0;
>> ioctl(fd, SYNC_IOC_FENCE_INFO, &info);
>> if (info.num_fences) {
>> info.sync_fence_info = (uintptr)kcalloc(info.num_fences, sizeof(struct sync_fence_info));
>> ioctl(fd, SYNC_IOC_FENCE_INFO, &info);
>> }
>>
>> Maybe userspace could preallocate the max in advance and set num_fences higher,
>>
>> kernel would do something like:
>>
>> num_fences = min(info.num_fences, sync->num_fences);
>> struct sync_fence_info array[num_fences];
>>
>> info.num_fences = sync->num_fences;
>> if (num_fences &&
>> copy_to_user((void * __user)(unsigned long)info.sync_fence_info, array, num_fences * sizeof(array)))
>> return -EFAULT;
> If we are going to call IOCTL twice I would actually have a new IOCTL only
> to fetch sync_fence_info.
>
> First we would call
>
> ioctl(fd, SYNC_IOC_FILE_INFO, &info);
>
> where info is:
>
> struct sync_file_info {
> char name[32];
> __s32 status;
> __u32 flags;
> __u32 num_fences;
> };
>
> then we would allocate a buffer with
>
> size = info.num_fences * sizeof(struct sync_fence_info)
>
> and call the new ioctl
>
> ioctl(fd, SYNC_IOC_SYNC_FENCE_INFO, sync_fence_info);
>
> This looks like a cleaner solution and doesn't break ABI. What do you
> think?
I think it's good taste that userspace specifies the size of the buffer it passes, so former feels more clean to me,
since you need to pass num_fences anyway.
But Daniel knows more about designing ioctl's than I do, so for exact behavior it's best to ask him.
~Maarten
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