From owner-freebsd-arch@FreeBSD.ORG Wed Dec 14 16:58:39 2011 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 40BF4106564A; Wed, 14 Dec 2011 16:58:39 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (mx0.zoral.com.ua [91.193.166.200]) by mx1.freebsd.org (Postfix) with ESMTP id D177B8FC14; Wed, 14 Dec 2011 16:58:38 +0000 (UTC) Received: from alf.home (alf.kiev.zoral.com.ua [10.1.1.177]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id pBEGwURr092286 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 14 Dec 2011 18:58:30 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: from alf.home (kostik@localhost [127.0.0.1]) by alf.home (8.14.5/8.14.5) with ESMTP id pBEGwUsl044803; Wed, 14 Dec 2011 18:58:30 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by alf.home (8.14.5/8.14.5/Submit) id pBEGwU2h044802; Wed, 14 Dec 2011 18:58:30 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: alf.home: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 14 Dec 2011 18:58:30 +0200 From: Kostik Belousov To: John Baldwin Message-ID: <20111214165830.GG50300@deviant.kiev.zoral.com.ua> References: <201112141141.41168.jhb@freebsd.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="hXPCCV0+y/03K5AN" Content-Disposition: inline In-Reply-To: <201112141141.41168.jhb@freebsd.org> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: clamav-milter 0.95.2 at skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-3.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: arch@freebsd.org Subject: Re: Changing lseek() to KNOTE on the vnode when seeking on a file X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 14 Dec 2011 16:58:39 -0000 --hXPCCV0+y/03K5AN Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Dec 14, 2011 at 11:41:41AM -0500, John Baldwin wrote: > A co-worker ran into an issue with using an EVFILT_READ kevent on a regul= ar=20 > file recently. Specifically, in the manpage it says: >=20 > EVFILT_READ Takes a descriptor as the identifier, and returns whe= never > there is data available to read. The behavior of the= fil- > ter is slightly different depending on the descriptor > type. >=20 > ... >=20 > Vnodes > Returns when the file pointer is not at the end of > file. data contains the offset from current posi= tion > to end of file, and may be negative. >=20 > He was then working on a program that read to EOF, then seeked back into = the > file. He was expecting to get a new kevent after seeking back into the f= ile > since for his file descriptor after the lseek "there is data available to= =20 > read" and "the file pointer is not at the end of file". I have a patch t= o fix=20 > this by doing a KNOTE() on a vnode after a successful seek. I checked OS= X=20 > and it looks like they added this to their lseek() in Snow Leopard > (http://fxr.watson.org/fxr/source/bsd/vfs/vfs_syscalls.c?v=3Dxnu-1699.24.= 8#L4182). >=20 > The one patch to fix this is below along with a test. Note that unlike O= S X > I did not add a new NOTE_NONE for this case. OS X has logic in their VFS > filter operations that make special assumptions about a hint value of 0, = so > they had to add NOTE_NONE as a hack. We do not have the same special=20 > assumptions about a hint of 0, so we can just use "0". Without this fix = the > test below complains about missing events for the "after seek" and "after= =20 > third read" cases. Just curious - wouldn't it generate a spurious event if lseek is performed with zero offset, e.g. SEEK_CUR with offset 0 ? --hXPCCV0+y/03K5AN Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD) iEYEARECAAYFAk7o1bYACgkQC3+MBN1Mb4hU0wCeMul5vUVedn8Ujcs7AXDNnY9f jXcAn16gdJFhDhRDXYdARMYi7bblzJQG =hP4y -----END PGP SIGNATURE----- --hXPCCV0+y/03K5AN--