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

[Glauber Costa <glauber@scylladb.com>]

On Fri, Jan 31, 2020 at 10:14 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> 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.

Yeah, I figured as much and ended up changing it.

>
> > 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
>