From owner-svn-src-all@freebsd.org Wed Apr 22 03:45:52 2020 Return-Path: Delivered-To: svn-src-all@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id DF7C62C4B2C; Wed, 22 Apr 2020 03:45:52 +0000 (UTC) (envelope-from kevans@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 496RDJ4t55z4cqP; Wed, 22 Apr 2020 03:45:52 +0000 (UTC) (envelope-from kevans@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id A26F0C80C; Wed, 22 Apr 2020 03:45:52 +0000 (UTC) (envelope-from kevans@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 03M3jqVb008174; Wed, 22 Apr 2020 03:45:52 GMT (envelope-from kevans@FreeBSD.org) Received: (from kevans@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 03M3jqrS008173; Wed, 22 Apr 2020 03:45:52 GMT (envelope-from kevans@FreeBSD.org) Message-Id: <202004220345.03M3jqrS008173@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: kevans set sender to kevans@FreeBSD.org using -f From: Kyle Evans Date: Wed, 22 Apr 2020 03:45:52 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r360182 - head/lib/libc/sys X-SVN-Group: head X-SVN-Commit-Author: kevans X-SVN-Commit-Paths: head/lib/libc/sys X-SVN-Commit-Revision: 360182 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Apr 2020 03:45:52 -0000 Author: kevans Date: Wed Apr 22 03:45:52 2020 New Revision: 360182 URL: https://svnweb.freebsd.org/changeset/base/360182 Log: kqueue(2): add a note about EV_RECEIPT In the below-referenced PR, a case is attached of a simple reproducer that exhibits suboptimal behavior: EVFILT_READ and EVFILT_WRITE being set in the same kevent(2) call will only honor the first one. This is, in-fact, how it's supposed to work. A read of the manpage leads me to believe we could be more clear about this; right now there's a logical leap to make in the relevant statement: "When passed as input, it forces EV_ERROR to always be returned." -- the logical leap being that this indicates the caller should have allocated space for the change to be returned with EV_ERROR indicated in the events, or subsequent filters will get dropped on the floor. Another possible workaround that accomplishes similar effect without needing space for all events is just setting EV_RECEIPT on the final change being passed in; if any errored before it, the kqueue would not be drained. If we made it to the final change with EV_RECEIPT set, then we would return that one with EV_ERROR and still not drain the kqueue. This would seem to not be all that advisable. PR: 229741 MFC after: 1 week Modified: head/lib/libc/sys/kqueue.2 Modified: head/lib/libc/sys/kqueue.2 ============================================================================== --- head/lib/libc/sys/kqueue.2 Wed Apr 22 00:42:10 2020 (r360181) +++ head/lib/libc/sys/kqueue.2 Wed Apr 22 03:45:52 2020 (r360182) @@ -24,7 +24,7 @@ .\" .\" $FreeBSD$ .\" -.Dd July 27, 2018 +.Dd April 21, 2020 .Dt KQUEUE 2 .Os .Sh NAME @@ -63,8 +63,7 @@ the event no longer holds, the kevent is removed from is not returned. .Pp Multiple events which trigger the filter do not result in multiple -kevents being placed on the kqueue; instead, the filter will aggregate -the events into a single struct kevent. +kevents being placed on the kqueue; instead, the filter wiApril 21, 2020the events into a single struct kevent. Calling .Fn close on a file descriptor will remove any kevents that reference the descriptor. @@ -233,6 +232,11 @@ to always be returned. When a filter is successfully added the .Va data field will be zero. +Note that if this flag is encountered and there is no remaining space in +.Fa eventlist +to hold the +.Dv EV_ERROR +event, then subsequent changes will not get processed. .It Dv EV_ONESHOT Causes the event to return only the first occurrence of the filter being triggered.