From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f45.google.com ([209.85.215.45]:36612 "EHLO mail-lf0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752743AbcFURXi (ORCPT ); Tue, 21 Jun 2016 13:23:38 -0400 Received: by mail-lf0-f45.google.com with SMTP id q132so33928706lfe.3 for ; Tue, 21 Jun 2016 10:23:36 -0700 (PDT) Received: from intelfx-laptop.local ([77.41.63.43]) by smtp.gmail.com with ESMTPSA id dw5sm1773825lbc.26.2016.06.21.10.23.34 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 21 Jun 2016 10:23:34 -0700 (PDT) Message-ID: <1466529808.27445.14.camel@intelfx.name> Subject: Rescue a single-device btrfs instance with zeroed tree root From: Ivan Shapovalov Reply-To: intelfx@intelfx.name To: linux-btrfs@vger.kernel.org Date: Tue, 21 Jun 2016 20:23:28 +0300 Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-dZenbF97IXtiqnbShwnW" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-dZenbF97IXtiqnbShwnW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello, So this is another case of "I lost my partition and do not have backups". More precisely, _this_ is the backup and it turned out to be damaged. (The backup was made by partclone.btrfs. Together with a zeroed out tree root, this asks for a bug in partclone...) So: the tree root is zeroes, backup roots are zeroes too, btrfs-find-root only reports blocks of level 0 (needed is 1). Is there something that can be done? Maybe it is possible to reconstruct the root from its children? Operations log following. Please Cc: me in replies as I'm not subscribed to the list. 1. regular mount # mount /dev/loop0p3 /mnt/temp =3D=3D=3D dmesg =3D=3D=3D [106737.299592] BTRFS info (device loop0p3): disk space caching is enabled [106737.299604] BTRFS: has skinny extents [106737.299884] BTRFS error (device loop0p3): bad tree block start 0 162633= 449472 [106737.299888] BTRFS: failed to read tree root on loop0p3 [106737.314359] BTRFS: open_ctree failed =3D=3D=3D end dmesg =3D=3D=3D 2. mount with -o recovery # mount -o recovery /dev/loop0p3 /mnt/temp =3D=3D=3D dmesg =3D=3D=3D [106742.305720] BTRFS warning (device loop0p3): 'recovery' is deprecated, u= se 'usebackuproot' instead [106742.305722] BTRFS info (device loop0p3): trying to use backup root at m= ount time [106742.305724] BTRFS info (device loop0p3): disk space caching is enabled [106742.305725] BTRFS: has skinny extents [106742.306056] BTRFS error (device loop0p3): bad tree block start 0 162633= 449472 [106742.306060] BTRFS: failed to read tree root on loop0p3 [106742.306069] BTRFS error (device loop0p3): bad tree block start 0 162633= 449472 [106742.306071] BTRFS: failed to read tree root on loop0p3 [106742.306084] BTRFS error (device loop0p3): bad tree block start 0 162632= 237056 [106742.306086] BTRFS: failed to read tree root on loop0p3 [106742.306097] BTRFS error (device loop0p3): bad tree block start 0 162626= 682880 [106742.306100] BTRFS: failed to read tree root on loop0p3 [106742.306111] BTRFS error (device loop0p3): bad tree block start 0 162609= 168384 [106742.306114] BTRFS: failed to read tree root on loop0p3 [106742.327272] BTRFS: open_ctree failed =3D=3D=3D end dmesg =3D=3D=3D 3. btrfs-find-root # btrfs-find-root /dev/loop0p3 Couldn't read tree root Superblock thinks the generation is 22332 Superblock thinks the level is 1 Well block 162633646080(gen: 22332 level: 0) seems good, but generation/lev= el doesn't match, want gen: 22332 level: 1 Well block 162633596928(gen: 22332 level: 0) seems good, but generation/lev= el doesn't match, want gen: 22332 level: 1 Well block 162633515008(gen: 22332 level: 0) seems good, but generation/lev= el doesn't match, want gen: 22332 level: 1 Thanks, --=20 Ivan Shapovalov / intelfx / --=-dZenbF97IXtiqnbShwnW Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAABCgAGBQJXaXgQAAoJEHveF8jk4w6dV6wQAKzZjXR+7ifq29RGTXcEZEq2 xG0Yp54FCRu0cAKq69WDbkC1VIUrt4/ZXIplUpwDBsSVYTbcUbjB2Fydl5S9cagX x9Nf3Td5IZV1rdzjkIj6pw4H7+6SMj2UKHmjVDwjzDJ5Uo1i6Rq1yMAbi8TqYd31 ARa0LJ2cQnOmwa/Xy3B0phNiahjSTbRcsksZ8g6YHeIvEWz4sPbz/Y5orQ2+s3o8 ZBYz3sWh020wSLILKdTvyxAxmWWv5Xv9kxCcfVQBfKiVO/Anj/EZS8FPIohUZavR GMBKSjc63um2e4eEHBYGnH102WWxZruHnrlArKRy63UEb3U9R1Ii2CGg4LMzV3kV Y8344fDi0a0/+UAs5XWt4LUmgbg5sF6cDWOSkmINZFgsdmsjXQns3wsaFM/qQeJg mXtTxfuTHNx7f/MwOo7RSyp3zbj9uzefz2L7HU0XuPAqC39eMZxP8fi9mIUaylWy loymFuUvV9ep1rMmG0K9zkYikMZhv1hih2qBdN6DbgwKnat0Ml/yNqQHzTR/k0Zr nst7gK3tB7BncZwHS3VtyAUHcvRsQuEwncxVJ2QyZUSxQCFsrF33ZB4l2YMKtKWd cEZ4aX/vkE8kuMJS3hJIjuWrQFZmMp8sMfFDc0sX5Xlzdv7gtmTMM+SwJI6e9dh5 dkmOyh5T7PCnYxojv4LG =cm9U -----END PGP SIGNATURE----- --=-dZenbF97IXtiqnbShwnW--