From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02860C433DF for ; Wed, 17 Jun 2020 01:40:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE8AD2100A for ; Wed, 17 Jun 2020 01:40:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726792AbgFQBj7 (ORCPT ); Tue, 16 Jun 2020 21:39:59 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:45838 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726601AbgFQBj4 (ORCPT ); Tue, 16 Jun 2020 21:39:56 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R411e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07425;MF=jiufei.xue@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0U.orvSE_1592357992; Received: from ali-186590e05fa3.local(mailfrom:jiufei.xue@linux.alibaba.com fp:SMTPD_---0U.orvSE_1592357992) by smtp.aliyun-inc.com(127.0.0.1); Wed, 17 Jun 2020 09:39:53 +0800 Subject: Re: [PATCH v3 1/2] io_uring: change the poll events to be 32-bits To: Pavel Begunkov , Jens Axboe , io-uring@vger.kernel.org Cc: joseph.qi@linux.alibaba.com References: <1591929018-73954-1-git-send-email-jiufei.xue@linux.alibaba.com> <1591929018-73954-2-git-send-email-jiufei.xue@linux.alibaba.com> <9e251ae9-ffe1-d9ea-feb5-cb9e641aeefb@kernel.dk> <7a311161-839c-3927-951d-3ce2bc7aa5d4@linux.alibaba.com> <967819fd-84c5-9329-60b6-899a2708849e@kernel.dk> <659bda5d-2da0-b092-9a66-1c4c4d89501a@kernel.dk> <5fc59f0b-7437-ac2c-a142-8cd7a532960c@kernel.dk> From: Jiufei Xue Message-ID: Date: Wed, 17 Jun 2020 09:39:52 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 2020/6/17 上午5:46, Pavel Begunkov wrote: > On 16/06/2020 22:21, Jens Axboe wrote: >> >> Nah this won't work, as the BE layout will be different. So how about >> this, just add a 16-bit poll_events_hi instead. App/liburing will set >> upper bits there. Something like the below, then just needs the >> exclusive wait change on top. >> >> Only downside I can see is that newer applications on older kernels will >> set EPOLLEXCLUSIVE but the kernel will ignore it. That's not a huge >> concern for this particular bit, but could be a concern if there are >> others that prove useful. >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index de1175206807..a9d74330ad6b 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -4809,6 +4809,9 @@ static int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe >> events = READ_ONCE(sqe->poll_events); >> poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP; >> >> + if (READ_ONCE(sqe->poll_events_hi) & EPOLLEXCLUSIVE) > > poll_events_hi is 16 bit, EPOLLEXCLUSIVE is (1 << 28). It's always false. > Do you look for something like below? > > > union { > ... > __u32 fsync_flags; > __u16 poll_events; /* compatibility */ > __u32 poll32_events; /* word-reversed for BE */ > }; > > u32 evs = READ_ONCE(poll32_events); > if (BIG_ENDIAN) > evs = swahw32(evs); // swap 16-bit halves > > // use as always, e.g. if (evs & EPOLLEXCLUSIVE) { ... } > Cool, That's clear. And we should do the reverse thing in liburing for big endian. I also want to add another feature bit in newer kernel, so that the newer application should check the feature first before setting the EPOLLEXCLUSIVE. Thanks, JIufei. >> + poll->events |= EPOLLEXCLUSIVE; >> + >> io_get_req_task(req); >> return 0; >> } >> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >> index 92c22699a5a7..e6856d8e068f 100644 >> --- a/include/uapi/linux/io_uring.h >> +++ b/include/uapi/linux/io_uring.h >> @@ -31,7 +31,10 @@ struct io_uring_sqe { >> union { >> __kernel_rwf_t rw_flags; >> __u32 fsync_flags; >> - __u16 poll_events; >> + struct { >> + __u16 poll_events; >> + __u16 poll_events_hi; >> + }; >> __u32 sync_range_flags; >> __u32 msg_flags; >> __u32 timeout_flags; >> >