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docs: update online directory and parent pointer repair sections

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Update the case studies of online directory and parent pointer
reconstruction to reflect what they actually do in the final version.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Darrick J. Wong
2024-04-15 14:55:08 -07:00
parent d85fe250f2
commit 5220727ce8
1 changed files with 29 additions and 26 deletions
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55
Documentation/filesystems/xfs/xfs-online-fsck-design.rst
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@ -4576,8 +4576,9 @@ Directory rebuilding uses a :ref:`coordinated inode scan <iscan>` and
a :ref:`directory entry live update hook <liveupdate>` as follows: a :ref:`directory entry live update hook <liveupdate>` as follows:
1. Set up a temporary directory for generating the new directory structure, 1. Set up a temporary directory for generating the new directory structure,
an xfblob for storing entry names, and an xfarray for stashing directory an xfblob for storing entry names, and an xfarray for stashing the fixed
updates. size fields involved in a directory update: ``(child inumber, add vs.
remove, name cookie, ftype)``.
2. Set up an inode scanner and hook into the directory entry code to receive 2. Set up an inode scanner and hook into the directory entry code to receive
updates on directory operations. updates on directory operations.
@ -4586,35 +4587,34 @@ a :ref:`directory entry live update hook <liveupdate>` as follows:
pointer references the directory of interest. pointer references the directory of interest.
If so: If so:
a. Stash an addname entry for this dirent in the xfarray for later. a. Stash the parent pointer name and an addname entry for this dirent in the
xfblob and xfarray, respectively.
b. When finished scanning that file, flush the stashed updates to the b. When finished scanning that file or the kernel memory consumption exceeds
temporary directory. a threshold, flush the stashed updates to the temporary directory.
4. For each live directory update received via the hook, decide if the child 4. For each live directory update received via the hook, decide if the child
has already been scanned. has already been scanned.
If so: If so:
a. Stash an addname or removename entry for this dirent update in the a. Stash the parent pointer name an addname or removename entry for this
xfarray for later. dirent update in the xfblob and xfarray for later.
We cannot write directly to the temporary directory because hook We cannot write directly to the temporary directory because hook
functions are not allowed to modify filesystem metadata. functions are not allowed to modify filesystem metadata.
Instead, we stash updates in the xfarray and rely on the scanner thread Instead, we stash updates in the xfarray and rely on the scanner thread
to apply the stashed updates to the temporary directory. to apply the stashed updates to the temporary directory.
5. When the scan is complete, atomically exchange the contents of the temporary 5. When the scan is complete, replay any stashed entries in the xfarray.
6. When the scan is complete, atomically exchange the contents of the temporary
directory and the directory being repaired. directory and the directory being repaired.
The temporary directory now contains the damaged directory structure. The temporary directory now contains the damaged directory structure.
6. Reap the temporary directory. 7. Reap the temporary directory.
7. Update the dirent position field of parent pointers as necessary.
This may require the queuing of a substantial number of xattr log intent
items.
The proposed patchset is the The proposed patchset is the
`parent pointers directory repair `parent pointers directory repair
<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=pptrs-online-dir-repair>`_ <https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=pptrs-fsck>`_
series. series.
Case Study: Repairing Parent Pointers Case Study: Repairing Parent Pointers
@ -4624,8 +4624,9 @@ Online reconstruction of a file's parent pointer information works similarly to
directory reconstruction: directory reconstruction:
1. Set up a temporary file for generating a new extended attribute structure, 1. Set up a temporary file for generating a new extended attribute structure,
an `xfblob<xfblob>` for storing parent pointer names, and an xfarray for an xfblob for storing parent pointer names, and an xfarray for stashing the
stashing parent pointer updates. fixed size fields involved in a parent pointer update: ``(parent inumber,
parent generation, add vs. remove, name cookie)``.
2. Set up an inode scanner and hook into the directory entry code to receive 2. Set up an inode scanner and hook into the directory entry code to receive
updates on directory operations. updates on directory operations.
@ -4634,34 +4635,36 @@ directory reconstruction:
dirent references the file of interest. dirent references the file of interest.
If so: If so:
a. Stash an addpptr entry for this parent pointer in the xfblob and xfarray a. Stash the dirent name and an addpptr entry for this parent pointer in the
for later. xfblob and xfarray, respectively.
b. When finished scanning the directory, flush the stashed updates to the b. When finished scanning the directory or the kernel memory consumption
temporary directory. exceeds a threshold, flush the stashed updates to the temporary file.
4. For each live directory update received via the hook, decide if the parent 4. For each live directory update received via the hook, decide if the parent
has already been scanned. has already been scanned.
If so: If so:
a. Stash an addpptr or removepptr entry for this dirent update in the a. Stash the dirent name and an addpptr or removepptr entry for this dirent
xfarray for later. update in the xfblob and xfarray for later.
We cannot write parent pointers directly to the temporary file because We cannot write parent pointers directly to the temporary file because
hook functions are not allowed to modify filesystem metadata. hook functions are not allowed to modify filesystem metadata.
Instead, we stash updates in the xfarray and rely on the scanner thread Instead, we stash updates in the xfarray and rely on the scanner thread
to apply the stashed parent pointer updates to the temporary file. to apply the stashed parent pointer updates to the temporary file.
5. Copy all non-parent pointer extended attributes to the temporary file. 5. When the scan is complete, replay any stashed entries in the xfarray.
6. When the scan is complete, atomically exchange the mappings of the attribute 6. Copy all non-parent pointer extended attributes to the temporary file.
7. When the scan is complete, atomically exchange the mappings of the attribute
forks of the temporary file and the file being repaired. forks of the temporary file and the file being repaired.
The temporary file now contains the damaged extended attribute structure. The temporary file now contains the damaged extended attribute structure.
7. Reap the temporary file. 8. Reap the temporary file.
The proposed patchset is the The proposed patchset is the
`parent pointers repair `parent pointers repair
<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=pptrs-online-parent-repair>`_ <https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=pptrs-fsck>`_
series. series.
Digression: Offline Checking of Parent Pointers Digression: Offline Checking of Parent Pointers