On 10/21/21 10:40 AM, John Keeping wrote: > On Wed, 20 Oct 2021 19:49:07 +0200 > Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> 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. So is there consensus on the USB side that we can just fill res2 with zero? The single cases that does just do res == res2 puts the error in res anyway, which is what you'd expect. If so, then I do think that'd be cleaner than packing two values into a u64. -- Jens Axboe
