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kernel-ark/Documentation/filesystems/ext4/orphan.rst

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ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
.. SPDX-License-Identifier: GPL-2.0
Orphan file
-----------
In unix there can inodes that are unlinked from directory hierarchy but that
are still alive because they are open. In case of crash the filesystem has to
clean up these inodes as otherwise they (and the blocks referenced from them)
would leak. Similarly if we truncate or extend the file, we need not be able
to perform the operation in a single journalling transaction. In such case we
track the inode as orphan so that in case of crash extra blocks allocated to
the file get truncated.
Traditionally ext4 tracks orphan inodes in a form of single linked list where
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
superblock contains the inode number of the last orphan inode (s_last_orphan
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
field) and then each inode contains inode number of the previously orphaned
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
inode (we overload i_dtime inode field for this). However this filesystem
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
global single linked list is a scalability bottleneck for workloads that result
in heavy creation of orphan inodes. When orphan file feature
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
(COMPAT_ORPHAN_FILE) is enabled, the filesystem has a special inode
(referenced from the superblock through s_orphan_file_inum) with several
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
blocks. Each of these blocks has a structure:
ext4: docs: switch away from list-table Commit 3a6541e97c03 (Add documentation about the orphan file feature) added a new document on orphan files, which is great. But the use of "list-table" results in documents that are absolutely unreadable in their plain-text form. Switch this file to the regular RST table format instead; the rendered (HTML) output is identical. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-2-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:53 +00:00
============= ================ =============== ===============================
Offset Type Name Description
============= ================ =============== ===============================
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
0x0 Array of Orphan inode Each __le32 entry is either
__le32 entries entries empty (0) or it contains
ext4: docs: switch away from list-table Commit 3a6541e97c03 (Add documentation about the orphan file feature) added a new document on orphan files, which is great. But the use of "list-table" results in documents that are absolutely unreadable in their plain-text form. Switch this file to the regular RST table format instead; the rendered (HTML) output is identical. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-2-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:53 +00:00
inode number of an orphan
inode.
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
blocksize-8 __le32 ob_magic Magic value stored in orphan
ext4: docs: switch away from list-table Commit 3a6541e97c03 (Add documentation about the orphan file feature) added a new document on orphan files, which is great. But the use of "list-table" results in documents that are absolutely unreadable in their plain-text form. Switch this file to the regular RST table format instead; the rendered (HTML) output is identical. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-2-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:53 +00:00
block tail (0x0b10ca04)
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
blocksize-4 __le32 ob_checksum Checksum of the orphan block.
ext4: docs: switch away from list-table Commit 3a6541e97c03 (Add documentation about the orphan file feature) added a new document on orphan files, which is great. But the use of "list-table" results in documents that are absolutely unreadable in their plain-text form. Switch this file to the regular RST table format instead; the rendered (HTML) output is identical. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-2-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:53 +00:00
============= ================ =============== ===============================
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
When a filesystem with orphan file feature is writeably mounted, we set
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
RO_COMPAT_ORPHAN_PRESENT feature in the superblock to indicate there may
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
be valid orphan entries. In case we see this feature when mounting the
filesystem, we read the whole orphan file and process all orphan inodes found
there as usual. When cleanly unmounting the filesystem we remove the
ext4: docs: Take out unneeded escaping The new file Documentation/orphan/ext4.rst escapes underscores ("\_") throughout. However, RST doesn't actually require that, so the escaping only succeeds in making the document less readable. Remove the unneeded escapes. Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210902220854.198850-3-corbet@lwn.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-09-02 22:08:54 +00:00
RO_COMPAT_ORPHAN_PRESENT feature to avoid unnecessary scanning of the orphan
ext4: Orphan file documentation Add documentation about the orphan file feature. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210816095713.16537-4-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2021-08-16 09:57:07 +00:00
file and also make the filesystem fully compatible with older kernels.
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