Re: [PATCH] add a helper function to verify io_uring functionality

[Jens Axboe <axboe@kernel.dk>]

On 1/29/20 12:20 PM, 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.
> 
> The boilerplate to do that is about always the same: find places that
> have feature bits, match that with what we need, rinse, repeat.
> Therefore it makes sense to move this to a library function.
> 
> We have two places in which we can check for such features: the feature
> flag returned by io_uring_init_params(), and the resulting array
> returning from io_uring_probe.
> 
> I tried my best to communicate as well as possible in the function
> signature the fact that this is not supposed to test the availability
> of io_uring (which is straightforward enough), but rather a minimum set
> of requirements for usage.

I wonder if we should have a helper that returns the fully allocated
io_uring_probe struct filled out by probing the kernel. My main worry
here is that some applications will probe for various things, each of
which will setup/teardown a ring, and do the query.

Maybe it'd be enough to potentially pass in a ring?

While this patch works with a sparse command opcode field, not sure it's
the most natural way. If we do the above, maybe we can just have a
is_this_op_supported() query, since it'd be cheap if we already have the
probe struct filled out?

Outside of this discussion, some style changes are needed:

- '*' goes next to the name, struct foo *ptr, not struct foo* ptr
- Some lines over 80 chars

-- 
Jens Axboe