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Add the seventh and final chapter of the online fsck documentation,
where we talk about future functionality that can tie in with the
functionality provided by the online fsck patchset.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Add the sixth chapter of the online fsck design documentation, where
we discuss the details of the data structures and algorithms used by the
driver program xfs_scrub.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Directory tree repairs are the least complete part of online fsck, due
to the lack of directory parent pointers. However, even without that
feature, we can still make some corrections to the directory tree -- we
can salvage as many directory entries as we can from a damaged
directory, and we can reattach orphaned inodes to the lost+found, just
as xfs_repair does now.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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File-based metadata (such as xattrs and directories) can be extremely
large. To reduce the memory requirements and maximize code reuse, it is
very convenient to create a temporary file, use the regular dir/attr
code to store salvaged information, and then atomically swap the extents
between the file being repaired and the temporary file. Record the high
level concepts behind how temporary files and atomic content swapping
should work, and then present some case studies of what the actual
repair functions do.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Certain parts of the online fsck code need to scan every file in the
entire filesystem. It is not acceptable to block the entire filesystem
while this happens, which means that we need to be clever in allowing
scans to coordinate with ongoing filesystem updates. We also need to
hook the filesystem so that regular updates propagate to the staging
records.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Add to the fifth chapter of the online fsck design documentation, where
we discuss the details of the data structures and algorithms used by the
kernel to repair file metadata.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Add a discussion of the btree bulk loading code, which makes it easy to
take an in-memory recordset and write it out to disk in an efficient
manner. This also enables atomic switchover from the old to the new
structure with minimal potential for leaking the old blocks.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Add a discussion of pageable kernel memory, since online fsck needs
quite a bit more memory than most other parts of the filesystem to stage
records and other information.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Writes to an XFS filesystem employ an eventual consistency update model
to break up complex multistep metadata updates into small chained
transactions. This is generally good for performance and scalability
because XFS doesn't need to prepare for enormous transactions, but it
also means that online fsck must be careful not to attempt a fsck action
unless it can be shown that there are no other threads processing a
transaction chain. This part of the design documentation covers the
thinking behind the consistency model and how scrub deals with it.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Begin the fifth chapter of the online fsck design documentation, where
we discuss the details of the data structures and algorithms used by the
kernel to examine filesystem metadata and cross-reference it around the
filesystem.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Start the fourth chapter of the online fsck design documentation, which
discusses the user interface and the background scrubbing service.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Start the third chapter of the online fsck design documentation. This
covers the testing plan to make sure that both online and offline fsck
can detect arbitrary problems and correct them without making things
worse.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Start the second chapter of the online fsck design documentation.
This covers the general theory underlying how online fsck works.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Start the first chapter of the online fsck design documentation.
This covers the motivations for creating this in the first place.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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