From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:45297 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751691AbeEVARI (ORCPT ); Mon, 21 May 2018 20:17:08 -0400 Received: by mail-pf0-f194.google.com with SMTP id c10-v6so7840461pfi.12 for ; Mon, 21 May 2018 17:17:08 -0700 (PDT) Date: Mon, 21 May 2018 17:17:06 -0700 From: Omar Sandoval To: linux-btrfs@vger.kernel.org Cc: kernel-team@fb.com, David Sterba , Tomohiro Misono Subject: Re: [PATCH] Btrfs: allow empty subvol= again Message-ID: <20180522001706.GD14774@vader> References: <4daab3c9993c97f3f962b16fcb9b5d578853765d.1526947478.git.osandov@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <4daab3c9993c97f3f962b16fcb9b5d578853765d.1526947478.git.osandov@fb.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, May 21, 2018 at 05:07:19PM -0700, Omar Sandoval wrote: > From: Omar Sandoval > > I got a report that after upgrading to 4.16, someone's filesystems > weren't mounting: > > [ 23.845852] BTRFS info (device loop0): unrecognized mount option 'subvol=' > > Before 4.16, this mounted the default subvolume. It turns out that this > empty "subvol=" is actually an application bug, but it was causing the > application to fail, so it's an ABI break if you squint. > > The generic parsing code we use for mount options (match_token()) > doesn't match an empty string as "%s". Previously, setup_root_args() > removed the "subvol=" string, but the mount path was cleaned up to not > need that. Add a dummy Opt_subvol_empty to fix this. > > Fixes: 312c89fbca06 ("btrfs: cleanup btrfs_mount() using btrfs_mount_root()") > Signed-off-by: Omar Sandoval > --- > Hi, Dave, > > This is silly but IMO it's a regression. If you agree, this should > probably go to 4.17 + stable. I'll submit an xfstests test shortly. > > Thanks! Update, we fixed the userspace bug now so I'd be fine if we dropped this patch. I guess there's still a possibility that there are other users that hit this, so I'll leave it up to you, Dave, whether it's important enough to care.