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=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 D8565C2D0E4 for ; Thu, 19 Nov 2020 10:48:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2155C246CE for ; Thu, 19 Nov 2020 10:48:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XCZpsAM7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2155C246CE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41388 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kfhUT-00086M-3P for qemu-devel@archiver.kernel.org; Thu, 19 Nov 2020 05:48:37 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:54294) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kfhQv-00059Q-GD for qemu-devel@nongnu.org; Thu, 19 Nov 2020 05:44:57 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:26099) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kfhQr-0002t2-AJ for qemu-devel@nongnu.org; Thu, 19 Nov 2020 05:44:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605782689; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=S8A6kUib9XH9HPGYz/o+koVf0KgN3JDBJqb05UG0mBQ=; b=XCZpsAM7Lsr0V+ypc+GUvqcvHo24b594JtASjjgw9cKvy1fkugmcyo514JBYeUwhHkFI+L CvCL/DfsATbTOZJ1LokInU1dxSl6ZRwqIIO1YZXFslGab8j7U8T1vsoy+hYP84jrVxAcv/ RLbfALRisAQTuzJ4yHcgKAfeRRPYusk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-105-vAFHwHp3MkmLmC_uhJ4I8g-1; Thu, 19 Nov 2020 05:44:45 -0500 X-MC-Unique: vAFHwHp3MkmLmC_uhJ4I8g-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8EEF18144F1; Thu, 19 Nov 2020 10:44:44 +0000 (UTC) Received: from merkur.fritz.box (ovpn-115-48.ams2.redhat.com [10.36.115.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8852A10016F5; Thu, 19 Nov 2020 10:44:43 +0000 (UTC) Date: Thu, 19 Nov 2020 11:44:42 +0100 From: Kevin Wolf To: Masayoshi Mizuma Subject: Re: [PATCH 1/2] file-posix: Use OFD lock only if the filesystem supports the lock Message-ID: <20201119104442.GB4530@merkur.fritz.box> References: <20201106040102.13892-1-msys.mizuma@gmail.com> <20201118154247.GB11988@merkur.fritz.box> <20201118191036.yk4rju2hk4vpkhfl@gabell> <20201118194837.b54rp2qpbvuelosx@gabell> MIME-Version: 1.0 In-Reply-To: <20201118194837.b54rp2qpbvuelosx@gabell> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/19 03:44:58 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Masayoshi Mizuma , qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 18.11.2020 um 20:48 hat Masayoshi Mizuma geschrieben: > On Wed, Nov 18, 2020 at 02:10:36PM -0500, Masayoshi Mizuma wrote: > > On Wed, Nov 18, 2020 at 04:42:47PM +0100, Kevin Wolf wrote: > > > Am 06.11.2020 um 05:01 hat Masayoshi Mizuma geschrieben: > > > > From: Masayoshi Mizuma > > > > > > > > locking=auto doesn't work if the filesystem doesn't support OFD lock. > > > > In that situation, following error happens: > > > > > > > > qemu-system-x86_64: -blockdev driver=qcow2,node-name=disk,file.driver=file,file.filename=/mnt/guest.qcow2,file.locking=auto: Failed to lock byte 100 > > > > > > > > qemu_probe_lock_ops() judges whether qemu can use OFD lock > > > > or not with doing fcntl(F_OFD_GETLK) to /dev/null. So the > > > > error happens if /dev/null supports OFD lock, but the filesystem > > > > doesn't support the lock. > > > > > > > > Lock the actual file, not /dev/null, using F_OFD_SETLK and if that > > > > fails, then fallback to F_SETLK. > > > > > > > > Signed-off-by: Masayoshi Mizuma > > > > -bool qemu_has_ofd_lock(void) > > > > -{ > > > > - qemu_probe_lock_ops(); > > > > #ifdef F_OFD_SETLK > > > > - return fcntl_op_setlk == F_OFD_SETLK; > > > > +static int _qemu_lock_fcntl(int fd, struct flock *fl) > > > > +{ > > > > + int ret; > > > > + bool ofd_lock = true; > > > > + > > > > + do { > > > > + if (ofd_lock) { > > > > + ret = fcntl(fd, F_OFD_SETLK, fl); > > > > + if ((ret == -1) && (errno == EINVAL)) { > > > > + ofd_lock = false; > > > > + } > > > > + } > > > > + > > > > + if (!ofd_lock) { > > > > + /* Fallback to POSIX lock */ > > > > + ret = fcntl(fd, F_SETLK, fl); > > > > + } > > > > + } while (ret == -1 && errno == EINTR); > > > > + > > > > + return ret == -1 ? -errno : 0; > > > > +} > > > > #else > > > > - return false; > > > > -#endif > > > > +static int _qemu_lock_fcntl(int fd, struct flock *fl) > > > > +{ > > > > + int ret; > > > > + > > > > + do { > > > > + ret = fcntl(fd, F_SETLK, fl); > > > > + } while (ret == -1 && errno == EINTR); > > > > + > > > > + return ret == -1 ? -errno : 0; > > > > } > > > > +#endif > > > > > > The logic looks fine to me, at least assuming that EINVAL is really what > > > we will consistently get from the kernel if OFD locks are not supported. > > > Is this documented anywhere? The fcntl manpage doesn't seem to mention > > > this case. > > The man page of fcntl(2) says: > > EINVAL The value specified in cmd is not recognized by this kernel. > > So I think EINVAL is good enough to check whether the filesystem supports > OFD locks or not... A kernel not knowing the cmd at all is a somewhat different case (and certainly a different code path) than a filesystem not supporting it. I just had a look at the kernel code, and to me it seems that the difference between POSIX locks and OFD locks is handled entirely in filesystem independent code. A filesystem driver would in theory have ways to distinguish both, but I don't see any driver in the kernel tree that actually does this (and there is probably little reason for a driver to do so). So now I wonder what filesystem you are using? I'm curious what I missed. Kevin