Re: [PATCH] fs: kill unused ret2 argument from iocb->ki_complete()

[Jeff Moyer <jmoyer@redhat.com>]

Jens Axboe <axboe@kernel.dk> writes:

> On 10/20/21 12:16 PM, Jeff Moyer wrote:
>> Hi, Jens,
>> 
>> Jens Axboe <axboe@kernel.dk> writes:
>> 
>>> It's not used for anything, and we're wasting time passing in zeroes
>>> where we could just ignore it instead. Update all ki_complete users in
>>> the kernel to drop that last argument.
>> 
>> What does "wasting time passing in zeroes" mean?
>
> That everybody but the funky usb gadget code passes in zero, hence it's
> a waste of time to pass it in as an argument.

OK.  Just making sure you hadn't found some performance gain from this.
:)

>> We can't know whether some userspace implementation relies on this
>> behavior, so I don't think you can change it.
>
> Well, I think we should find out, particularly as it's the sole user of
> that extra argument.

How can we find out?  Anyone can write userspace usb gadget code.  Some
of those users may be proprietary.  Is that likely?  I don't know.  I'd
rather err on the side of not (potentially) breaking existing
applications, though.

> No generic aio code would look at res2, exactly because it is always
> zero for anything but some weird usb gadget code.

I think that no generic code looks at it because it isn't meant to be
interpreted by generic code.  :)

-Jeff