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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 D2D29C43460 for ; Fri, 21 May 2021 08:51:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3E08613AC for ; Fri, 21 May 2021 08:51:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233956AbhEUIwY (ORCPT ); Fri, 21 May 2021 04:52:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233815AbhEUIwX (ORCPT ); Fri, 21 May 2021 04:52:23 -0400 Received: from mail-vs1-xe36.google.com (mail-vs1-xe36.google.com [IPv6:2607:f8b0:4864:20::e36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BE32DC061763 for ; Fri, 21 May 2021 01:50:45 -0700 (PDT) Received: by mail-vs1-xe36.google.com with SMTP id s15so9980919vsi.4 for ; Fri, 21 May 2021 01:50:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=szeredi.hu; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mFPnGBBo9uPK7q1bx3/OHNBziL1VS1FaR/jW/45G8No=; b=Zk2iAnAYEgvulBteJzqiLG+YcF0Ge6ONYvZ2Cwv9EegLGu04xZ46iosv1yP+M/Cwo1 gDqkELTiUclVGOOcOD5+zDlFcEvVuobHjKQetErpTDXYmOrE9yyPHTnsmet7bty32vgX vD4peK29KWDUju0YLfeYstIJQiIln2ZJvkO0o= 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=mFPnGBBo9uPK7q1bx3/OHNBziL1VS1FaR/jW/45G8No=; b=eT3p6ZuvwyBJ0JOj9UWjd6l3DH6IPM/dikGl1EPx3+BXrBSvm8HJFGxgLOHJ3fODSM HZC7+wHSqUE7rBJoSD19xEer9BccOMOkQp8otPkevJVBksJ6c7n2YFijH+P8H/0Bsikx n0MO4Q8601bRVII0QhufpnnwN0BpGbGBhUj7PrdhRXINLfVT2WGweKlReGp9dUd6p/NS GGhBMnNTD5j+/X4RoLQqwWCi0gwPo4ojKNsvpc7T7s45jgrgSPWj/Ddt89HCwlsYNKFl lSjA9sGvQK8qBu703on40d2m+2BM8xBxLpJByVmEjk2qiM4qL9O+WUwDGTrFalTH8sld sloQ== X-Gm-Message-State: AOAM531E1T3tbkjubmDtkDus9aT10GpKjfuOH7YurCS5e8n/iKNUOQlx Ma5y2q9xf81XB6krBkZcegdLNHq2+6puETSgIf4OGQ== X-Google-Smtp-Source: ABdhPJzP8cEKt6HEzMuSAdCnzlwE1Q7BGhy6FcshRLFe8hP1JWwWgnnZk9hiwMntEVdIPB7+uiVNg8pi50V7JB0yuDw= X-Received: by 2002:a05:6102:3239:: with SMTP id x25mr8079662vsf.47.1621587044884; Fri, 21 May 2021 01:50:44 -0700 (PDT) MIME-Version: 1.0 References: <20210520154654.1791183-1-groug@kaod.org> <20210520154654.1791183-5-groug@kaod.org> <20210521103921.153a243d@bahia.lan> In-Reply-To: <20210521103921.153a243d@bahia.lan> From: Miklos Szeredi Date: Fri, 21 May 2021 10:50:34 +0200 Message-ID: Subject: Re: [PATCH v4 4/5] virtiofs: Skip submounts in sget_fc() To: Greg Kurz Cc: virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, virtio-fs-list , Stefan Hajnoczi , Max Reitz , Vivek Goyal Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, 21 May 2021 at 10:39, Greg Kurz wrote: > > On Fri, 21 May 2021 10:26:27 +0200 > Miklos Szeredi wrote: > > > On Thu, 20 May 2021 at 17:47, Greg Kurz wrote: > > > > > > All submounts share the same virtio-fs device instance as the root > > > mount. If the same virtiofs filesystem is mounted again, sget_fc() > > > is likely to pick up any of these submounts and reuse it instead of > > > the root mount. > > > > > > On the server side: > > > > > > # mkdir ${some_dir} > > > # mkdir ${some_dir}/mnt1 > > > # mount -t tmpfs none ${some_dir}/mnt1 > > > # touch ${some_dir}/mnt1/THIS_IS_MNT1 > > > # mkdir ${some_dir}/mnt2 > > > # mount -t tmpfs none ${some_dir}/mnt2 > > > # touch ${some_dir}/mnt2/THIS_IS_MNT2 > > > > > > On the client side: > > > > > > # mkdir /mnt/virtiofs1 > > > # mount -t virtiofs myfs /mnt/virtiofs1 > > > # ls /mnt/virtiofs1 > > > mnt1 mnt2 > > > # grep virtiofs /proc/mounts > > > myfs /mnt/virtiofs1 virtiofs rw,seclabel,relatime 0 0 > > > none on /mnt/mnt1 type virtiofs (rw,relatime,seclabel) > > > none on /mnt/mnt2 type virtiofs (rw,relatime,seclabel) > > > > > > And now remount it again: > > > > > > # mount -t virtiofs myfs /mnt/virtiofs2 > > > # grep virtiofs /proc/mounts > > > myfs /mnt/virtiofs1 virtiofs rw,seclabel,relatime 0 0 > > > none on /mnt/mnt1 type virtiofs (rw,relatime,seclabel) > > > none on /mnt/mnt2 type virtiofs (rw,relatime,seclabel) > > > myfs /mnt/virtiofs2 virtiofs rw,seclabel,relatime 0 0 > > > # ls /mnt/virtiofs2 > > > THIS_IS_MNT2 > > > > > > Submount mnt2 was picked-up instead of the root mount. > > > > > Why is this a problem? > > > > It seems very weird to mount the same filesystem again > and to end up in one of its submounts. We should have: > > # ls /mnt/virtiofs2 > mnt1 mnt2 Okay, sorry, I understand the problem. The solution is wrong, however: the position of the submount on that list is no indication that it's the right one (it's possible that the root sb will go away and only a sub-sb will remain). Even just setting a flag in the root, indicating that it's the root isn't fully going to solve the problem. Here's issue in full: case 1: no connection for "myfs" exists - need to create fuse_conn, sb case 2: connection for "myfs" exists but only sb for submount - only create sb for root, reuse fuse_conn case 3: connection for "myfs" as well as root sb exists - reuse sb I'll think about how to fix this properly, it's probably going to be rather more involved... Thanks, Miklos