From owner-freebsd-hackers@freebsd.org Wed Jan 2 15:00:15 2019 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5F08014232F9 for ; Wed, 2 Jan 2019 15:00:15 +0000 (UTC) (envelope-from asomers@gmail.com) Received: from mail-lf1-f65.google.com (mail-lf1-f65.google.com [209.85.167.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 250458F9A1 for ; Wed, 2 Jan 2019 15:00:14 +0000 (UTC) (envelope-from asomers@gmail.com) Received: by mail-lf1-f65.google.com with SMTP id y14so2170830lfg.13 for ; Wed, 02 Jan 2019 07:00:14 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6W8X90LMItygF6fH7t8PRTEaDElJ1va3s2EEg/o7Xfs=; b=D4/AVKVwuUHn2lfizjzj97/j8ExbBfluQcl10snvvXDXTOZTZ4mzarqIhqL9nB3prP 9wkPMoy9Nghl7uA+CmvphwmLewxjVrOVkdkNLFPGl4PPsVshBbSoIsGyqGmJYf3qzpcc 6NUByqT22ZmD3iQD1PpkDFb8khIvI8s+YzmjBXNjB4hWZze4KFe3EsnWX1c1exoVuB9h /Vdv+zb47GgTmKVxyr8d0KFt1abuyrsMmVwl1fhK6usIOfLBdjlkSDfqp+/DVIw+gcZH 9GkMJx6kPxOvIwHvaw2Dp5Q3+63bOMXxXFZ6cyz+mRqXPUL3el0msOrRaopOkRRtEmCs E0Cg== X-Gm-Message-State: AA+aEWZyrGY9TbYIbC+WoXkXRKpHlWzhQ7pOoyX+NtCmiPAzB+lLmiqO 8f7Po330yQT7ETQlmepHaeTwUP4hAQWjAw1lK20OfA== X-Google-Smtp-Source: AFSGD/U1aDBQ+94PZv5yyNcPX+tHj872DM0XAd2xuCUI+41HaTv/3axEO5ei7oDrwoly1MxTqKg7A6+oMJRr5UQa3GQ= X-Received: by 2002:a19:200b:: with SMTP id g11mr21163434lfg.58.1546441206752; Wed, 02 Jan 2019 07:00:06 -0800 (PST) MIME-Version: 1.0 References: <8753521a-4555-ec2a-5efc-dee2660b4d9b@digiware.nl> <969d9a38-d3dd-78d0-c974-ba14ec4747db@digiware.nl> <016fda76-8f02-ca62-af7d-062262bd4a09@digiware.nl> In-Reply-To: <016fda76-8f02-ca62-af7d-062262bd4a09@digiware.nl> From: Alan Somers Date: Wed, 2 Jan 2019 07:59:55 -0700 Message-ID: Subject: Re: Using kqueue with aio_read/write To: Willem Jan Withagen Cc: FreeBSD Hackers Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 250458F9A1 X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; spf=pass (mx1.freebsd.org: domain of asomers@gmail.com designates 209.85.167.65 as permitted sender) smtp.mailfrom=asomers@gmail.com X-Spamd-Result: default: False [-4.01 / 15.00]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; FROM_HAS_DN(0.00)[]; R_SPF_ALLOW(-0.20)[+ip4:209.85.128.0/17]; NEURAL_HAM_LONG(-1.00)[-0.998,0]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; DMARC_NA(0.00)[freebsd.org]; MIME_TRACE(0.00)[0:+]; TO_DN_ALL(0.00)[]; MX_GOOD(-0.01)[cached: alt3.gmail-smtp-in.l.google.com]; RCPT_COUNT_TWO(0.00)[2]; RCVD_IN_DNSWL_NONE(0.00)[65.167.85.209.list.dnswl.org : 127.0.5.0]; NEURAL_HAM_SHORT(-0.90)[-0.904,0]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_TLS_LAST(0.00)[]; FORGED_SENDER(0.30)[asomers@freebsd.org,asomers@gmail.com]; R_DKIM_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; FROM_NEQ_ENVFROM(0.00)[asomers@freebsd.org,asomers@gmail.com]; IP_SCORE(-1.10)[ipnet: 209.85.128.0/17(-3.78), asn: 15169(-1.61), country: US(-0.08)]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Jan 2019 15:00:15 -0000 On Wed, Jan 2, 2019 at 5:53 AM Willem Jan Withagen wrote: > > On 02/01/2019 03:23, Alan Somers wrote: > > On Tue, Jan 1, 2019 at 6:56 PM Willem Jan Withagen wrote: > >> On 28/12/2018 02:47, Alan Somers wrote: > >>> On Thu, Dec 27, 2018 at 6:15 PM Willem Jan Withagen wrote: > >>>> Hi, > >>>> > >>>> Im trying to understand why I cannot get so code to work. > >>>> This is the smallest extract I can make to show my problem. > >>>> > >>>> I would expect the kevent() call to return every timeo tick. > >>>> Even if I tell it NOT to time-out I get these spurts of errors > >>>> > >>>> Since there is nothing to trigger the AIO-event, I would expect kqueue > >>>> to hold indefinitly. > >>>> > >>>> But it does not generate anything other than errors > >>>> And instead it repeatedly complains that there is a permission error: > >>>> get_events_kevent: EV_Error(1) kevent(): Operation not permitted > >>>> > >>>> But I'm not getting where that would the case... > >>>> > >>>> Surely a pilot error, but I do overlook it al the time. > >>>> So suggestions are welcome. > >>>> > >>>> Thanx, > >>>> --WjW > >>>> > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> > >>>> #define BUFFER_SIZE 512 > >>>> #define MAX_EVENTS 32 > >>>> > >>>> #define FILENAME "/tmp/aio_test" > >>>> char filename[256]; > >>>> int fd; > >>>> int done = 0; > >>>> > >>>> void get_events_kevent(int fd, int kq) > >>>> { > >>>> printf("get_events function fd = %d, kq = %d\n", fd, kq); > >>>> int i = 0, errcnt = 0, err, ret, reterr, rev; > >>>> int search = 1; > >>>> > >>>> int timeout_ms = 10; > >>>> struct timespec timeo = { > >>>> timeout_ms / 1000, > >>>> (timeout_ms % 1000) * 1000 * 1000 > >>>> }; > >>>> struct kevent filter[16]; > >>>> struct kevent changed[16]; > >>>> > >>>> EV_SET(&filter[0], fd, EVFILT_AIO, > >>>> EV_ADD, > >>>> 0, 0, 0 ); > >>> This is the first problem. There's no need to explicitly set > >>> EVFILT_AIO on the kqueue. It gets set by the aio_read(2) or similar > >>> syscall. And this invocation wouldn't be correct anyway, because for > >>> AIO the ident field refers to the address of the struct aiocb, not the > >>> file descriptor. If the only events you care about are AIO, then you > >>> can pass NULL as the filter argument to kevent. I suspect this is the > >>> cause of your problem. The kernel probably thinks you're trying to > >>> register for an aiocb that's outside of your address space or > >>> something like that. > >>> > >>> > >>>> while (!done) { > >>>> printf("+"); > >>>> rev = kevent(kq, filter, 1, changed, 16, 0); //&timeo); > >>>> if (rev < 0) { > >>>> perror("kevent error"); > >>>> } else if (rev == 0) { > >>>> printf("T"); > >>>> } else { > >>>> printf("rev(%d)\n", rev); > >>>> if (changed[0].flags == EV_ERROR) { > >>>> errno = changed[0].data; > >>>> printf( "%s: EV_Error(%d) kevent(): %s\n", __func__, errno, > >>>> strerror(errno)); > >>>> memset(&changed[0], 0, sizeof(struct kevent)); > >>>> } else { > >>>> err = aio_error((struct aiocb*)changed[0].udata); > >>> No need to call aio_error(2) after kevent(2) returns. You can go > >>> straight to aio_return. aio_error shouldn't hurt, but it isn't > >>> necessary. > >> According to kevent(2) calling kevent can return errors on the called > >> aio_calls. > >> It then returns with EV_ERROR in flags, and errno is stored in the > >> event.data. > >> > >> But what would be going on when the event's flag contains EV_ERROR but > >> event's data is still 0??? > >> > >> the udata field still seems to point to the aio data that was passed > >> into the aio block when calling aio_read(). > >> > >> Should I ignore this as a non-error? > >> > >> --WjW > > Are you sure you bzero()ed your aiocb before initializing it? Any > > stack garbage that was present in its > > aio_sigevent.sigev_notify_kevent_flags field will be dutifully copied > > into the returned kevent. And in any case, the definitive way to get > > the final status of a completed aio operation is with aio_return. > That seems to help in getting things clear... > > -13> 2019-01-02 13:32:31.834 dc15a80 1 bdev:327 paio > get_next_completed processing event i = 0 aio_return(22) (22) Invalid > argument > > Disadvantage is that it is not clear yet which of the many arguments > that is? > > --WjW It could be failing for any reason that read(2) can fail. Or, the iocb might not be complete. aio_error(2) would tell you. One common problem is if you allocate the iocb on the stack and accidentally move it after calling aio_read(). That's bitten me before. -Alan