[PATCH v6 3/3] io_uring: enable per-io hinting capability

[Kanchan Joshi]

On 9/25/2024 5:53 PM, Pavel Begunkov wrote:
> On 9/25/24 12:09, Kanchan Joshi wrote:
>> On 9/25/2024 11:27 AM, Hannes Reinecke wrote:
> ...
>> As it stands the new struct will introduce
>>> a hole of 24 bytes after 'hint_type'.
>>
>> This gets implicitly padded at this point [1][2], and overall size is
>> still capped by largest struct (which is of 16 bytes, placed just above
>> this).
> 
> For me it's about having hardly usable in the future by anyone else
> 7 bytes of space or how much that will be. Try to add another field
> using those bytes and endianess will start messing with you. And 7
> bytes is not that convenient.
> 
> I have same problem with how commands were merged while I was not
> looking. There was no explicit padding, and it split u64 into u32
> and implicit padding, so no apps can use the space to put a pointer
> anymore while there was a much better option of using one of existing
> 4B fields.

How would you prefer it. Explicit padding (7 bytes), hint_type as u16 or 
anything else?