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=-11.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 DE2A7C388F7 for ; Tue, 10 Nov 2020 18:59:12 +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 0AB4320780 for ; Tue, 10 Nov 2020 18:59:11 +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="GMibUU0N" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0AB4320780 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]:56462 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kcYrG-0002Sj-Ur for qemu-devel@archiver.kernel.org; Tue, 10 Nov 2020 13:59:10 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:44598) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcYqE-0001xM-Gj for qemu-devel@nongnu.org; Tue, 10 Nov 2020 13:58:06 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:56213) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kcYqC-00038o-6d for qemu-devel@nongnu.org; Tue, 10 Nov 2020 13:58:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605034683; 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=aa+RUdUNxJOTALfCtpEy9ZGiraJLA2yP/vNjt7f55+g=; b=GMibUU0N1mtp8Mjp1IyqfEdZ5RVF1NzMV0To/+ixU8QMaSZ1bVl//pxq1bBf4VjEDSJ6ZI eDGrS8PlRI8ye7d2D6kYNSMsOqTD38ZFhZeMccTvBA40WWZUDzw1z2OVd1mHVVA8p07/h5 VAjKJFuXgVFTeXiEedmTr6XpSd55PIk= 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-135-_D3ndhLMPHuEiLFps01USg-1; Tue, 10 Nov 2020 13:58:00 -0500 X-MC-Unique: _D3ndhLMPHuEiLFps01USg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2713910866AD for ; Tue, 10 Nov 2020 18:57:59 +0000 (UTC) Received: from work-vm (ovpn-115-49.ams2.redhat.com [10.36.115.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D31BA6EF43; Tue, 10 Nov 2020 18:57:51 +0000 (UTC) Date: Tue, 10 Nov 2020 18:57:49 +0000 From: "Dr. David Alan Gilbert" To: Max Reitz Subject: Re: [PATCH for-5.2] virtiofsd: Announce submounts even without statx() Message-ID: <20201110185749.GH3108@work-vm> References: <20201103164135.169325-1-mreitz@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201103164135.169325-1-mreitz@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@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=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/10 02:00:53 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: virtio-fs@redhat.com, Miklos Szeredi , qemu-devel@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Max Reitz (mreitz@redhat.com) wrote: > Contrary to what the check (and warning) in lo_init() claims, we can > announce submounts just fine even without statx() -- the check is based > on comparing both the mount ID and st_dev of parent and child. Without > statx(), we will not have the mount ID; but we always have st_dev. > > The only problems we have (without statx() and its mount ID) are: > > (1) Mounting the same device twice may lead to both trees being treated > as exactly the same tree by virtiofsd. But that is a problem that > is completely independent of mirroring host submounts in the guest. > Both submount roots will still show the FUSE_SUBMOUNT flag, because > their st_dev still differs from their respective parent. > > (2) There is only one exception to (1), and that is if you mount a > device inside a mount of itself: Then, its st_dev will be the same > as that of its parent, and so without a mount ID, virtiofsd will not > be able to recognize the nested mount's root as a submount. > However, thanks to virtiofsd then treating both trees as exactly the > same tree, it will be caught up in a loop when the guest tries to > examine the nested submount, so the guest will always see nothing > but an ELOOP there. Therefore, this case is just fully broken > without statx(), whether we check for submounts (based on st_dev) or > not. > > All in all, checking for submounts works well even without comparing the > mount ID (i.e., without statx()). The only concern is an edge case > that, without statx() mount IDs, is utterly broken anyway. > > Thus, drop said check in lo_init(). > > Reported-by: Miklos Szeredi > Signed-off-by: Max Reitz OK, that seems to have been the outcome of the discussion here: https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg00500.html so Reviewed-by: Dr. David Alan Gilbert > --- > tools/virtiofsd/passthrough_ll.c | 8 -------- > 1 file changed, 8 deletions(-) > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index ec1008bceb..6c64b03f1a 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -610,14 +610,6 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) > "does not support it\n"); > lo->announce_submounts = false; > } > - > -#ifndef CONFIG_STATX > - if (lo->announce_submounts) { > - fuse_log(FUSE_LOG_WARNING, "lo_init: Cannot announce submounts, there " > - "is no statx()\n"); > - lo->announce_submounts = false; > - } > -#endif > } > > static void lo_getattr(fuse_req_t req, fuse_ino_t ino, > -- > 2.26.2 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK