Re: [PATCH v2 liburing] add helper functions to verify io_uring functionality

[Jens Axboe <axboe@kernel.dk>]

On 1/31/20 6:52 AM, Glauber Costa wrote:
> On Thu, Jan 30, 2020 at 11:31 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 1/30/20 9:29 AM, Glauber Costa wrote:
>>> On Thu, Jan 30, 2020 at 11:13 AM Jens Axboe <axboe@kernel.dk> wrote:
>>>>
>>>> On 1/30/20 9:00 AM, Glauber Costa wrote:
>>>>> It is common for an application using an ever-evolving interface to want
>>>>> to inquire about the presence of certain functionality it plans to use.
>>>>>
>>>>> Information about opcodes is stored in a io_uring_probe structure. There
>>>>> is usually some boilerplate involved in initializing one, and then using
>>>>> it to check if it is enabled.
>>>>>
>>>>> This patch adds two new helper functions: one that returns a pointer to
>>>>> a io_uring_probe (or null if it probe is not available), and another one
>>>>> that given a probe checks if the opcode is supported.
>>>>
>>>> This looks good, I committed it with minor changes.
>>>>
>>>> On top of this, we should have a helper that doesn't need a ring. So
>>>> basically one that just sets up a ring, calls io_uring_get_probe(),
>>>> then tears down the ring.
>>>>
>>> I'd be happy to follow up with that.
>>>
>>> Just to be sure, the information returned by probe should be able to outlive the
>>> tear down of the ring, right ?
>>
>> Yeah, same lifetime as the helper you have now, caller must free it once
>> done.
> 
> Well, in hindsight, I should have called that
> io_uring_get_probe_ring() so io_uring_get_probe()
> doesn't take a ring.

Just change it - we just added it yesterday, and it's not released yet.
I don't break anything that's been in a release, and I maintain
compatibility between releases, but we can change it now.

> Alternatively, to keep things in a single function, I can change
> io_uring_get_probe() so that if it
> ring is NULL, we do our own allocation.
> 
> I actually kind of like that. Would that work for you ?

Not a huge deal to me, we can go that route.

-- 
Jens Axboe