From: John Keeping <john@metanate.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-usb@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] fs: kill unused ret2 argument from iocb->ki_complete()
Date: Thu, 21 Oct 2021 17:40:21 +0100 [thread overview]
Message-ID: <20211021174021.273c82b1.john@metanate.com> (raw)
In-Reply-To: <YXBWk8Zzi7yIyTi/@kroah.com>
On Wed, 20 Oct 2021 19:49:07 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> On Wed, Oct 20, 2021 at 11:35:27AM -0600, Jens Axboe wrote:
> > On 10/20/21 11:30 AM, Christoph Hellwig wrote:
> > > On Wed, Oct 20, 2021 at 10:49:07AM -0600, Jens Axboe wrote:
> > >> 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.
> > >>
> > >> The exception is the USB gadget code, which passes in non-zero. But
> > >> since nobody every looks at ret2, it's still pointless.
> > >
> > > Yes, the USB gadget passes non-zero, and aio passes that on to
> > > userspace. So this is an ABI change. Does it actually matter?
> > > I don't know, but you could CC the relevant maintainers and list
> > > to try to figure that out.
> >
> > True, guess it does go out to userspace. Greg, is anyone using
> > it on the userspace side?
>
> I really do not know (adding linux-usb@vger) My interactions with the
> gadget code have not been through the aio api, thankfully :)
>
> Odds are it's fine, I think that something had to be passed in there so
> that was chosen? If the aio code didn't do anything with it, I can't
> see where the gadget code gets it back at anywhere, but I might be
> looking in the wrong place.
>
> Anyone else here know?
I really doubt anyone uses io_event::res2 with FunctionFS gadgets. The
examples in tools/usb/ffs-aio-example/ either check just "res" or ignore
the status completely.
The only other program I can find using aio FunctionFS is adbd which
also checks res and ignores res2 [1]. Other examples I know of just use
synchronous I/O.
[1] https://github.com/aosp-mirror/platform_system_core/blob/34a0e57a257f0081c672c9be0e87230762e677ca/adb/daemon/usb.cpp#L527
next prev parent reply other threads:[~2021-10-21 16:40 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-20 16:49 [PATCH] fs: kill unused ret2 argument from iocb->ki_complete() Jens Axboe
2021-10-20 17:30 ` Christoph Hellwig
2021-10-20 17:35 ` Jens Axboe
2021-10-20 17:49 ` Greg Kroah-Hartman
2021-10-21 16:40 ` John Keeping [this message]
2021-10-21 16:56 ` Jens Axboe
2021-10-22 15:44 ` Jens Axboe
2021-10-23 9:09 ` Greg Kroah-Hartman
2021-10-23 14:01 ` Jens Axboe
2021-10-20 18:16 ` Jeff Moyer
2021-10-20 18:21 ` Jens Axboe
2021-10-20 18:37 ` Jeff Moyer
2021-10-20 18:41 ` Jens Axboe
2021-10-20 18:56 ` Jens Axboe
2021-10-20 19:11 ` Jeff Moyer
2021-10-20 19:12 ` Jens Axboe
2021-10-20 19:47 ` Jeff Moyer
2021-10-20 19:54 ` Jens Axboe
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