On 7/1/22 12:05 PM, Darrick J. Wong wrote: > On Fri, Jul 01, 2022 at 08:38:07AM -0600, Jens Axboe wrote: >> On 7/1/22 8:30 AM, Jens Axboe wrote: >>> On 7/1/22 8:19 AM, Jens Axboe wrote: >>>> On 6/30/22 10:39 PM, Al Viro wrote: >>>>> On Wed, Jun 01, 2022 at 02:01:41PM -0700, Stefan Roesch wrote: >>>>>> This adds the async buffered write support to XFS. For async buffered >>>>>> write requests, the request will return -EAGAIN if the ilock cannot be >>>>>> obtained immediately. >>>>> >>>>> breaks generic/471... >>>> >>>> That test case is odd, because it makes some weird assumptions about >>>> what RWF_NOWAIT means. Most notably that it makes it mean if we should >>>> instantiate blocks or not. Where did those assumed semantics come from? >>>> On the read side, we have clearly documented that it should "not wait >>>> for data which is not immediately available". >>>> >>>> Now it is possible that we're returning a spurious -EAGAIN here when we >>>> should not be. And that would be a bug imho. I'll dig in and see what's >>>> going on. >>> >>> This is the timestamp update that needs doing which will now return >>> -EAGAIN if IOCB_NOWAIT is set as it may block. >>> >>> I do wonder if we should just allow inode time updates with IOCB_NOWAIT, >>> even on the io_uring side. Either that, or passed in RWF_NOWAIT >>> semantics don't map completely to internal IOCB_NOWAIT semantics. At >>> least in terms of what generic/471 is doing, but I'm not sure who came >>> up with that and if it's established semantics or just some made up ones >>> from whomever wrote that test. I don't think they make any sense, to be >>> honest. >> >> Further support that generic/471 is just randomly made up semantics, >> it needs to special case btrfs with nocow or you'd get -EAGAIN anyway >> for that test. >> >> And it's relying on some random timing to see if this works. I really >> think that test case is just hot garbage, and doesn't test anything >> meaningful. > > <shrug> I had thought that NOWAIT means "don't wait for *any*thing", > which would include timestamp updates... but then I've never been all > that clear on what specifically NOWAIT will and won't wait for. :/ Agree, at least the read semantics (kind of) make sense, but the ones seemingly made up by generic/471 don't seem to make any sense at all. -- Jens Axboe
