On 3/4/20 1:09 PM, Josh Triplett wrote: > On Wed, Mar 04, 2020 at 01:00:05PM -0700, Jens Axboe wrote: >> On 3/4/20 12:56 PM, Josh Triplett wrote: >>> On Wed, Mar 04, 2020 at 12:10:08PM -0700, Jens Axboe wrote: >>>> On 3/4/20 12:03 PM, Josh Triplett wrote: >>>>> On Wed, Mar 04, 2020 at 11:00:10AM -0700, Jens Axboe wrote: >>>>>> One of the fabled features with chains has long been the desire to >>>>>> support things like: >>>>>> >>>>>> <open fileX><read from fileX><close fileX> >>>>>> >>>>>> in a single chain. This currently doesn't work, since the read/close >>>>>> depends on what file descriptor we get on open. >>>>>> >>>>>> The original attempt at solving this provided a means to pass >>>>>> descriptors between chains in a link, this version takes a different >>>>>> route. Based on Josh's support for O_SPECIFIC_FD, we can instead control >>>>>> what fd value we're going to get out of open (or accept). With that in >>>>>> place, we don't need to do any magic to make this work. The above chain >>>>>> then becomes: >>>>>> >>>>>> <open fileX with fd Y><read from fd Y><close fd Y> >>>>>> >>>>>> which is a lot more useful, and allows any sort of weird chains without >>>>>> needing to nest "last open" file descriptors. >>>>>> >>>>>> Updated the test program to use this approach: >>>>>> >>>>>> https://git.kernel.dk/cgit/liburing/plain/test/orc.c?h=fd-select >>>>>> >>>>>> which forces the use of fd==89 for the open, and then uses that for the >>>>>> read and close. >>>>>> >>>>>> Outside of this adaptation, fixed a few bugs and cleaned things up. >>>>> >>>>> I posted one comment about an issue in patch 6. >>>>> >>>>> Patches 2-5 look great; for those: >>>>> Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> >>>>> >>>>> Thanks for picking this up and running with it! >>>> >>>> Thanks for doing the prep work! I think it turned out that much better >>>> for it. >>>> >>>> Are you going to post your series for general review? I just stole >>>> your 1 patch that was needed for me. >>> >>> Since your patch series depends on mine, please feel free to run with >>> the series. Would you mind adding my patch 1 and 3 at the end of your >>> series? You need patch 1 to make this more usable for userspace, and >>> patch 3 would allow for an OP_PIPE which I'd love to have. >> >> Let me add patch 1 to the top of the stack, for the pipe part that >> probably should be taken in separately. But not a huge deal to me, >> as long as we can get it reviewed. > > That works for me; I don't mind if the pipe support goes in a bit later. > And there are many other fd-producing syscalls that need support for > userspace-selected FDs, including signalfd4, eventfd2, timerfd_create, > epoll_create1, memfd_create, userfaultfd, and the pidfd family. Right, at least on the io_uring front, adding IORING_OP_SOCKET and providing support for SOCK_SPECIFIC_FD through that would be trivial and a few lines of change. In general, we can more easily do all that through io_uring, as we have room to shove in that extra 'fd'. I've queued up patch 1 as well. >>> Do you plan to submit this during the next merge window? >> >> Maybe? In terms of timing, I think we're well within the opportunity >> to do so, at least. > > I look forward to seeing it go in. Me too :-) -- Jens Axboe
