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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2CAE5CD13D9 for ; Mon, 18 Sep 2023 22:51:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229772AbjIRWvL (ORCPT ); Mon, 18 Sep 2023 18:51:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229450AbjIRWvK (ORCPT ); Mon, 18 Sep 2023 18:51:10 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9CF991 for ; Mon, 18 Sep 2023 15:51:04 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 67CE122313; Mon, 18 Sep 2023 22:51:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1695077463; h=from:from:reply-to:reply-to: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=WZbNskK7JLB0BclP2+lm5vjoHWkke5n1hbWC1m68JDg=; b=DYQVaCLhzVunvGyXAls2UnirckNGFoq9tvChjL79cd0HZyXPGuVs5HHHQ7pAWAEjZZ42W/ ZIFlS0GWNvwc83jl0+6R+p2DqV4Upy5FDxz9rHBOttDqTT+jB9noCQxlLLcN/NHqp18WwO 4DwJ1q6xphaBpZ/H8Mgw+9rGlWVnCYo= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1695077463; h=from:from:reply-to:reply-to: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=WZbNskK7JLB0BclP2+lm5vjoHWkke5n1hbWC1m68JDg=; b=3V/SZdFXBh1E59A8DhPxdUq5TE7MYqHACy/GcBvATO05dzw0FbIAv4ACAUtUvvGU7hAZx/ D0CwRf9YeCpP4XDw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 328E813480; Mon, 18 Sep 2023 22:51:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id UOJ9ClfUCGXWGwAAMHmgww (envelope-from ); Mon, 18 Sep 2023 22:51:03 +0000 Date: Tue, 19 Sep 2023 00:44:27 +0200 From: David Sterba To: Anand Jain Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: reject device with CHANGING_FSID_V2 Message-ID: <20230918224427.GS2747@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <02d59bdd7a8b778deb17e300354558498db59376.1692178060.git.anand.jain@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <02d59bdd7a8b778deb17e300354558498db59376.1692178060.git.anand.jain@oracle.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Wed, Aug 16, 2023 at 08:30:40PM +0800, Anand Jain wrote: > The BTRFS_SUPER_FLAG_CHANGING_FSID_V2 flag indicates a transient state > where the device in the userspace btrfstune -m|-M operation failed to > complete changing the fsid. > > This flag makes the kernel to automatically determine the other > partner devices to which a given device can be associated, based on the > fsid, metadata_uuid and generation values. > > btrfstune -m|M feature is especially useful in virtual cloud setups, where > compute instances (disk images) are quickly copied, fsid changed, and > launched. Given numerous disk images with the same metadata_uuid but > different fsid, there's no clear way a device can be correctly assembled > with the proper partners when the CHANGING_FSID_V2 flag is set. So, the > disk could be assembled incorrectly, as in the example below: > > Before this patch: > > Consider the following two filesystems: > /dev/loop[2-3] are raw copies of /dev/loop[0-1] and the btrsftune -m > operation fails. > > In this scenario, as the /dev/loop0's fsid change is interrupted, and the > CHANGING_FSID_V2 flag is set as shown below. > > $ p="device|devid|^metadata_uuid|^fsid|^incom|^generation|^flags" > > $ btrfs inspect dump-super /dev/loop0 | egrep '$p' > superblock: bytenr=65536, device=/dev/loop0 > flags 0x1000000001 > fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 > metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b > generation 9 > num_devices 2 > incompat_flags 0x741 > dev_item.devid 1 > > $ btrfs inspect dump-super /dev/loop1 | egrep '$p' > superblock: bytenr=65536, device=/dev/loop1 > flags 0x1 > fsid 11d2af4d-1b71-45a9-83f6-f2100766939d > metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b > generation 10 > num_devices 2 > incompat_flags 0x741 > dev_item.devid 2 > > $ btrfs inspect dump-super /dev/loop2 | egrep '$p' > superblock: bytenr=65536, device=/dev/loop2 > flags 0x1 > fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 > metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b > generation 8 > num_devices 2 > incompat_flags 0x741 > dev_item.devid 1 > > $ btrfs inspect dump-super /dev/loop3 | egrep '$p' > superblock: bytenr=65536, device=/dev/loop3 > flags 0x1 > fsid 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 > metadata_uuid bb040a9f-233a-4de2-ad84-49aa5a28059b > generation 8 > num_devices 2 > incompat_flags 0x741 > dev_item.devid 2 > > > It is normal that some devices aren't instantly discovered during > system boot or iSCSI discovery. The controlled scan below demonstrates > this. > > $ btrfs device scan --forget > $ btrfs device scan /dev/loop0 > Scanning for btrfs filesystems on '/dev/loop0' > $ mount /dev/loop3 /btrfs > $ btrfs filesystem show -m > Label: none uuid: 7d4b4b93-2b27-4432-b4e4-4be1fbccbd45 > Total devices 2 FS bytes used 144.00KiB > devid 1 size 300.00MiB used 48.00MiB path /dev/loop0 > devid 2 size 300.00MiB used 40.00MiB path /dev/loop3 > > /dev/loop0 and /dev/loop3 are incorrectly partnered. > > This kernel patch removes functions and code connected to the > CHANGING_FSID_V2 flag. > > With this patch, now devices with the CHANGING_FSID_V2 flag are rejected. > And its partner will fail to mount with the extra -o degraded option. > > Signed-off-by: Anand Jain > --- > Moreover, a btrfs-progs patch (below) has eliminated the use of the > CHANGING_FSID_V2 flag entirely: > > [PATCH RFC] btrfs-progs: btrfstune -m|M remove 2-stage commit > > And we solve the compatability concerns as below: > > New-kernel new-progs - has no CHANGING_FSID_V2 flag. > Old-kernel new-progs - has no CHANGING_FSID_V2 flag, kernel code unused. > Old-kernel old-progs - bug may occur. > New-kernel old-progs - Should use host with the newer btrfs-progs to fix. > > For legacy systems to help fix such a condition in the userspace instead > we have the below patchset which ports of kernel's CHANGING_FSID_V2 code. > > [PATCH 00/16] btrfs-progs: recover from failed metadata_uuid > > And if it couldn't fix in some cases, users can use manually reunite, > with the patchset: > > [PATCH 00/10] btrfs-progs: check and tune: add device and noscan options > > fs/btrfs/disk-io.c | 10 --- > fs/btrfs/volumes.c | 166 ++++----------------------------------------- > fs/btrfs/volumes.h | 1 - > 3 files changed, 13 insertions(+), 164 deletions(-) Please split the kernel patch in two, one rejecting the CHANGING_FSID_V2 bit and then removing the unused code. I think the scanning code still has to recognize the bit and skip the device, I haven't checked if remains like that after this patch.