From: "Darrick J. Wong" <djwong@kernel.org>
To: chandanbabu@kernel.org, djwong@kernel.org
Cc: Christoph Hellwig <hch@lst.de>, hch@lst.de, linux-xfs@vger.kernel.org
Subject: [PATCH 1/4] docs: update the parent pointers documentation to the final version
Date: Mon, 15 Apr 2024 16:56:41 -0700 [thread overview]
Message-ID: <171322386129.91896.14510868533818236418.stgit@frogsfrogsfrogs> (raw)
In-Reply-To: <171322386102.91896.17539357886365049977.stgit@frogsfrogsfrogs>
From: Darrick J. Wong <djwong@kernel.org>
Now that we've decided on the ondisk format of parent pointers, update
the documentation to reflect that.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
.../filesystems/xfs/xfs-online-fsck-design.rst | 94 +++++++++++---------
1 file changed, 53 insertions(+), 41 deletions(-)
diff --git a/Documentation/filesystems/xfs/xfs-online-fsck-design.rst b/Documentation/filesystems/xfs/xfs-online-fsck-design.rst
index 74a8e42c74bd..1e3211d12247 100644
--- a/Documentation/filesystems/xfs/xfs-online-fsck-design.rst
+++ b/Documentation/filesystems/xfs/xfs-online-fsck-design.rst
@@ -4465,10 +4465,10 @@ reconstruction of filesystem space metadata.
The parent pointer feature, however, makes total directory reconstruction
possible.
-XFS parent pointers include the dirent name and location of the entry within
-the parent directory.
+XFS parent pointers contain the information needed to identify the
+corresponding directory entry in the parent directory.
In other words, child files use extended attributes to store pointers to
-parents in the form ``(parent_inum, parent_gen, dirent_pos) → (dirent_name)``.
+parents in the form ``(dirent_name) → (parent_inum, parent_gen)``.
The directory checking process can be strengthened to ensure that the target of
each dirent also contains a parent pointer pointing back to the dirent.
Likewise, each parent pointer can be checked by ensuring that the target of
@@ -4476,8 +4476,6 @@ each parent pointer is a directory and that it contains a dirent matching
the parent pointer.
Both online and offline repair can use this strategy.
-**Note**: The ondisk format of parent pointers is not yet finalized.
-
+--------------------------------------------------------------------------+
| **Historical Sidebar**: |
+--------------------------------------------------------------------------+
@@ -4519,8 +4517,58 @@ Both online and offline repair can use this strategy.
| Chandan increased the maximum extent counts of both data and attribute |
| forks, thereby ensuring that the extended attribute structure can grow |
| to handle the maximum hardlink count of any file. |
+| |
+| For this second effort, the ondisk parent pointer format as originally |
+| proposed was ``(parent_inum, parent_gen, dirent_pos) → (dirent_name)``. |
+| The format was changed during development to eliminate the requirement |
+| of repair tools needing to to ensure that the ``dirent_pos`` field |
+| always matched when reconstructing a directory. |
+| |
+| There were a few other ways to have solved that problem: |
+| |
+| 1. The field could be designated advisory, since the other three values |
+| are sufficient to find the entry in the parent. |
+| However, this makes indexed key lookup impossible while repairs are |
+| ongoing. |
+| |
+| 2. We could allow creating directory entries at specified offsets, which |
+| solves the referential integrity problem but runs the risk that |
+| dirent creation will fail due to conflicts with the free space in the |
+| directory. |
+| |
+| These conflicts could be resolved by appending the directory entry |
+| and amending the xattr code to support updating an xattr key and |
+| reindexing the dabtree, though this would have to be performed with |
+| the parent directory still locked. |
+| |
+| 3. Same as above, but remove the old parent pointer entry and add a new |
+| one atomically. |
+| |
+| 4. Change the ondisk xattr format to |
+| ``(parent_inum, name) → (parent_gen)``, which would provide the attr |
+| name uniqueness that we require, without forcing repair code to |
+| update the dirent position. |
+| Unfortunately, this requires changes to the xattr code to support |
+| attr names as long as 263 bytes. |
+| |
+| 5. Change the ondisk xattr format to ``(parent_inum, hash(name)) → |
+| (name, parent_gen)``. |
+| If the hash is sufficiently resistant to collisions (e.g. sha256) |
+| then this should provide the attr name uniqueness that we require. |
+| Names shorter than 247 bytes could be stored directly. |
+| |
+| 6. Change the ondisk xattr format to ``(dirent_name) → (parent_ino, |
+| parent_gen)``. This format doesn't require any of the complicated |
+| nested name hashing of the previous suggestions. However, it was |
+| discovered that multiple hardlinks to the same inode with the same |
+| filename caused performance problems with hashed xattr lookups, so |
+| the parent inumber is now xor'd into the hash index. |
+| |
+| In the end, it was decided that solution #6 was the most compact and the |
+| most performant. A new hash function was designed for parent pointers. |
+--------------------------------------------------------------------------+
+
Case Study: Repairing Directories with Parent Pointers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -4569,42 +4617,6 @@ The proposed patchset is the
<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=pptrs-online-dir-repair>`_
series.
-**Unresolved Question**: How will repair ensure that the ``dirent_pos`` fields
-match in the reconstructed directory?
-
-*Answer*: There are a few ways to solve this problem:
-
-1. The field could be designated advisory, since the other three values are
- sufficient to find the entry in the parent.
- However, this makes indexed key lookup impossible while repairs are ongoing.
-
-2. We could allow creating directory entries at specified offsets, which solves
- the referential integrity problem but runs the risk that dirent creation
- will fail due to conflicts with the free space in the directory.
-
- These conflicts could be resolved by appending the directory entry and
- amending the xattr code to support updating an xattr key and reindexing the
- dabtree, though this would have to be performed with the parent directory
- still locked.
-
-3. Same as above, but remove the old parent pointer entry and add a new one
- atomically.
-
-4. Change the ondisk xattr format to ``(parent_inum, name) → (parent_gen)``,
- which would provide the attr name uniqueness that we require, without
- forcing repair code to update the dirent position.
- Unfortunately, this requires changes to the xattr code to support attr
- names as long as 263 bytes.
-
-5. Change the ondisk xattr format to ``(parent_inum, hash(name)) →
- (name, parent_gen)``.
- If the hash is sufficiently resistant to collisions (e.g. sha256) then
- this should provide the attr name uniqueness that we require.
- Names shorter than 247 bytes could be stored directly.
-
-Discussion is ongoing under the `parent pointers patch deluge
-<https://www.spinics.net/lists/linux-xfs/msg69397.html>`_.
-
Case Study: Repairing Parent Pointers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
next prev parent reply other threads:[~2024-04-15 23:56 UTC|newest]
Thread overview: 103+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 23:28 [PATCHBOMB v30.3] xfs: online repair, part 1 is done Darrick J. Wong
2024-04-15 23:33 ` [PATCHSET v30.3 01/16] xfs: improve log incompat feature handling Darrick J. Wong
2024-04-15 23:37 ` [PATCH 1/5] xfs: pass xfs_buf lookup flags to xfs_*read_agi Darrick J. Wong
2024-04-15 23:38 ` [PATCH 2/5] xfs: fix an AGI lock acquisition ordering problem in xrep_dinode_findmode Darrick J. Wong
2024-04-15 23:38 ` [PATCH 3/5] xfs: fix potential AGI <-> ILOCK ABBA deadlock in xrep_dinode_findmode_walk_directory Darrick J. Wong
2024-04-15 23:38 ` [PATCH 4/5] xfs: fix error bailout in xrep_abt_build_new_trees Darrick J. Wong
2024-04-15 23:38 ` [PATCH 5/5] xfs: only clear log incompat flags at clean unmount Darrick J. Wong
2024-04-15 23:34 ` [PATCHSET v30.3 02/16] xfs: refactorings for atomic file content exchanges Darrick J. Wong
2024-04-15 23:39 ` [PATCH 1/7] xfs: move inode lease breaking functions to xfs_inode.c Darrick J. Wong
2024-04-15 23:39 ` [PATCH 2/7] xfs: move xfs_iops.c declarations out of xfs_inode.h Darrick J. Wong
2024-04-15 23:39 ` [PATCH 3/7] xfs: declare xfs_file.c symbols in xfs_file.h Darrick J. Wong
2024-04-15 23:40 ` [PATCH 4/7] xfs: create a new helper to return a file's allocation unit Darrick J. Wong
2024-04-15 23:40 ` [PATCH 5/7] xfs: hoist multi-fsb allocation unit detection to a helper Darrick J. Wong
2024-04-15 23:40 ` [PATCH 6/7] xfs: refactor non-power-of-two alignment checks Darrick J. Wong
2024-04-15 23:40 ` [PATCH 7/7] xfs: constify xfs_bmap_is_written_extent Darrick J. Wong
2024-04-15 23:34 ` [PATCHSET v30.3 03/16] xfs: atomic file content exchanges Darrick J. Wong
2024-04-15 23:41 ` [PATCH 01/15] vfs: export remap and write check helpers Darrick J. Wong
2024-04-15 23:41 ` [PATCH 02/15] xfs: introduce new file range exchange ioctl Darrick J. Wong
2024-04-15 23:41 ` [PATCH 03/15] xfs: create a incompat flag for atomic file mapping exchanges Darrick J. Wong
2024-04-15 23:41 ` [PATCH 04/15] xfs: introduce a file mapping exchange log intent item Darrick J. Wong
2024-04-15 23:42 ` [PATCH 05/15] xfs: create deferred log items for file mapping exchanges Darrick J. Wong
2024-04-15 23:42 ` [PATCH 06/15] xfs: bind together the front and back ends of the file range exchange code Darrick J. Wong
2024-04-15 23:42 ` [PATCH 07/15] xfs: add error injection to test file mapping exchange recovery Darrick J. Wong
2024-04-15 23:42 ` [PATCH 08/15] xfs: condense extended attributes after a mapping exchange operation Darrick J. Wong
2024-04-15 23:43 ` [PATCH 09/15] xfs: condense directories " Darrick J. Wong
2024-04-15 23:43 ` [PATCH 10/15] xfs: condense symbolic links " Darrick J. Wong
2024-04-15 23:43 ` [PATCH 11/15] xfs: make file range exchange support realtime files Darrick J. Wong
2024-04-15 23:43 ` [PATCH 12/15] xfs: support non-power-of-two rtextsize with exchange-range Darrick J. Wong
2024-04-15 23:44 ` [PATCH 13/15] xfs: capture inode generation numbers in the ondisk exchmaps log item Darrick J. Wong
2024-04-15 23:44 ` [PATCH 14/15] docs: update swapext -> exchmaps language Darrick J. Wong
2024-04-15 23:44 ` [PATCH 15/15] xfs: enable logged file mapping exchange feature Darrick J. Wong
2024-04-15 23:34 ` [PATCHSET v30.3 04/16] xfs: create temporary files for online repair Darrick J. Wong
2024-04-15 23:44 ` [PATCH 1/4] xfs: hide private inodes from bulkstat and handle functions Darrick J. Wong
2024-04-15 23:45 ` [PATCH 2/4] xfs: create temporary files and directories for online repair Darrick J. Wong
2024-04-15 23:45 ` [PATCH 3/4] xfs: refactor live buffer invalidation for repairs Darrick J. Wong
2024-04-15 23:45 ` [PATCH 4/4] xfs: add the ability to reap entire inode forks Darrick J. Wong
2024-04-15 23:34 ` [PATCHSET v30.3 05/16] xfs: online repair of realtime summaries Darrick J. Wong
2024-04-15 23:46 ` [PATCH 1/3] xfs: support preallocating and copying content into temporary files Darrick J. Wong
2024-04-15 23:46 ` [PATCH 2/3] xfs: teach the tempfile to set up atomic file content exchanges Darrick J. Wong
2024-04-15 23:46 ` [PATCH 3/3] xfs: online repair of realtime summaries Darrick J. Wong
2024-04-15 23:35 ` [PATCHSET v30.3 06/16] xfs: set and validate dir/attr block owners Darrick J. Wong
2024-04-15 23:46 ` [PATCH 01/10] xfs: add an explicit owner field to xfs_da_args Darrick J. Wong
2024-04-15 23:47 ` [PATCH 02/10] xfs: use the xfs_da_args owner field to set new dir/attr block owner Darrick J. Wong
2024-04-15 23:47 ` [PATCH 03/10] xfs: reduce indenting in xfs_attr_node_list Darrick J. Wong
2024-04-15 23:47 ` [PATCH 04/10] xfs: validate attr leaf buffer owners Darrick J. Wong
2024-04-15 23:47 ` [PATCH 05/10] xfs: validate attr remote value " Darrick J. Wong
2024-04-15 23:48 ` [PATCH 06/10] xfs: validate dabtree node " Darrick J. Wong
2024-04-15 23:48 ` [PATCH 07/10] xfs: validate directory leaf " Darrick J. Wong
2024-04-15 23:48 ` [PATCH 08/10] xfs: validate explicit directory data " Darrick J. Wong
2024-04-15 23:48 ` [PATCH 09/10] xfs: validate explicit directory block " Darrick J. Wong
2024-04-15 23:49 ` [PATCH 10/10] xfs: validate explicit directory free block owners Darrick J. Wong
2024-04-15 23:35 ` [PATCHSET v30.3 07/16] xfs: online repair of extended attributes Darrick J. Wong
2024-04-15 23:49 ` [PATCH 1/7] xfs: enable discarding of folios backing an xfile Darrick J. Wong
2024-04-15 23:49 ` [PATCH 2/7] xfs: create a blob array data structure Darrick J. Wong
2024-04-15 23:49 ` [PATCH 3/7] xfs: use atomic extent swapping to fix user file fork data Darrick J. Wong
2024-04-15 23:50 ` [PATCH 4/7] xfs: repair extended attributes Darrick J. Wong
2024-04-15 23:50 ` [PATCH 5/7] xfs: scrub should set preen if attr leaf has holes Darrick J. Wong
2024-04-15 23:50 ` [PATCH 6/7] xfs: flag empty xattr leaf blocks for optimization Darrick J. Wong
2024-04-15 23:50 ` [PATCH 7/7] xfs: create an xattr iteration function for scrub Darrick J. Wong
2024-04-15 23:35 ` [PATCHSET v30.3 08/16] xfs: online repair of inode unlinked state Darrick J. Wong
2024-04-15 23:51 ` [PATCH 1/2] xfs: ensure unlinked list state is consistent with nlink during scrub Darrick J. Wong
2024-04-15 23:51 ` [PATCH 2/2] xfs: update the unlinked list when repairing link counts Darrick J. Wong
2024-04-15 23:35 ` [PATCHSET v30.3 09/16] xfs: online repair of directories Darrick J. Wong
2024-04-15 23:51 ` [PATCH 1/5] xfs: inactivate directory data blocks Darrick J. Wong
2024-04-15 23:52 ` [PATCH 2/5] xfs: online repair of directories Darrick J. Wong
2024-04-15 23:52 ` [PATCH 3/5] xfs: scan the filesystem to repair a directory dotdot entry Darrick J. Wong
2024-04-15 23:52 ` [PATCH 4/5] xfs: online repair of parent pointers Darrick J. Wong
2024-04-15 23:52 ` [PATCH 5/5] xfs: ask the dentry cache if it knows the parent of a directory Darrick J. Wong
2024-04-15 23:36 ` [PATCHSET v30.3 10/16] xfs: move orphan files to lost and found Darrick J. Wong
2024-04-15 23:53 ` [PATCH 1/3] xfs: move orphan files to the orphanage Darrick J. Wong
2024-04-15 23:53 ` [PATCH 2/3] xfs: move files to orphanage instead of letting nlinks drop to zero Darrick J. Wong
2024-04-15 23:53 ` [PATCH 3/3] xfs: ensure dentry consistency when the orphanage adopts a file Darrick J. Wong
2024-04-15 23:36 ` [PATCHSET v30.3 11/16] xfs: online repair of symbolic links Darrick J. Wong
2024-04-15 23:53 ` [PATCH 1/3] xfs: expose xfs_bmap_local_to_extents for online repair Darrick J. Wong
2024-04-15 23:54 ` [PATCH 2/3] xfs: pass the owner to xfs_symlink_write_target Darrick J. Wong
2024-04-15 23:54 ` [PATCH 3/3] xfs: online repair of symbolic links Darrick J. Wong
2024-04-15 23:36 ` [PATCHSET v30.3 12/16] xfs: online fsck of iunlink buckets Darrick J. Wong
2024-04-15 23:54 ` [PATCH 1/3] xfs: check AGI unlinked inode buckets Darrick J. Wong
2024-04-15 23:54 ` [PATCH 2/3] xfs: hoist AGI repair context to a heap object Darrick J. Wong
2024-04-15 23:55 ` [PATCH 3/3] xfs: repair AGI unlinked inode bucket lists Darrick J. Wong
2024-04-15 23:36 ` [PATCHSET v30.3 13/16] xfs: inode-related repair fixes Darrick J. Wong
2024-04-15 23:55 ` [PATCH 1/4] xfs: check unused nlink fields in the ondisk inode Darrick J. Wong
2024-04-15 23:55 ` [PATCH 2/4] xfs: try to avoid allocating from sick inode clusters Darrick J. Wong
2024-04-15 23:55 ` [PATCH 3/4] xfs: pin inodes that would otherwise overflow link count Darrick J. Wong
2024-04-15 23:56 ` [PATCH 4/4] xfs: create subordinate scrub contexts for xchk_metadata_inode_subtype Darrick J. Wong
2024-04-15 23:37 ` [PATCHSET v30.3 14/16] xfs: less heavy locks during fstrim Darrick J. Wong
2024-04-15 23:56 ` [PATCH 1/1] xfs: fix performance problems when fstrimming a subset of a fragmented AG Darrick J. Wong
2024-04-15 23:37 ` [PATCHSET v13.2 15/16] xfs: design documentation for online fsck, part 2 Darrick J. Wong
2024-04-15 23:56 ` Darrick J. Wong [this message]
2024-04-15 23:56 ` [PATCH 2/4] docs: update online directory and parent pointer repair sections Darrick J. Wong
2024-04-15 23:57 ` [PATCH 3/4] docs: update offline parent pointer repair strategy Darrick J. Wong
2024-04-15 23:57 ` [PATCH 4/4] docs: describe xfs directory tree online fsck Darrick J. Wong
2024-04-15 23:37 ` [PATCHSET v13.2 16/16] xfs: retain ILOCK during directory updates Darrick J. Wong
2024-04-15 23:57 ` [PATCH 1/7] xfs: Increase XFS_DEFER_OPS_NR_INODES to 5 Darrick J. Wong
2024-04-15 23:57 ` [PATCH 2/7] xfs: Increase XFS_QM_TRANS_MAXDQS " Darrick J. Wong
2024-04-15 23:58 ` [PATCH 3/7] xfs: Hold inode locks in xfs_ialloc Darrick J. Wong
2024-04-15 23:58 ` [PATCH 4/7] xfs: Hold inode locks in xfs_trans_alloc_dir Darrick J. Wong
2024-04-15 23:58 ` [PATCH 5/7] xfs: Hold inode locks in xfs_rename Darrick J. Wong
2024-04-15 23:59 ` [PATCH 6/7] xfs: don't pick up IOLOCK during rmapbt repair scan Darrick J. Wong
2024-04-15 23:59 ` [PATCH 7/7] xfs: unlock new repair tempfiles after creation Darrick J. Wong
-- strict thread matches above, loose matches on Subject: below --
2024-04-10 0:44 [PATCHSET v13.1 1/9] xfs: design documentation for online fsck, part 2 Darrick J. Wong
2024-04-10 0:46 ` [PATCH 1/4] docs: update the parent pointers documentation to the final version Darrick J. Wong
2024-04-10 4:40 ` Christoph Hellwig
2023-12-31 19:32 [PATCHSET v13.0 1/7] xfs: design documentation for online fsck, part 2 Darrick J. Wong
2023-12-31 20:42 ` [PATCH 1/4] docs: update the parent pointers documentation to the final version Darrick J. Wong
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