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. [1] https://github.com/aosp-mirror/platform_system_core/blob/34a0e57a257f0081c672c9be0e87230762e677ca/adb/daemon/usb.cpp#L527
