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authorGirish Shilamkar <girish@clusterfs.com>2008-01-28 23:58:27 -0500
committerTheodore Ts'o <tytso@mit.edu>2008-01-28 23:58:27 -0500
commit818d276ceb83aa9fdebb5e0a53188290312de987 (patch)
treede3fb4ffadd72caea2876c5232ce76cd14b3646e /Documentation/filesystems
parent8e85fb3f305b24b79c6d9cb7a56d22b062335ad3 (diff)
ext4: Add the journal checksum feature
The journal checksum feature adds two new flags i.e JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT and JBD2_FEATURE_COMPAT_CHECKSUM. JBD2_FEATURE_CHECKSUM flag indicates that the commit block contains the checksum for the blocks described by the descriptor blocks. Due to checksums, writing of the commit record no longer needs to be synchronous. Now commit record can be sent to disk without waiting for descriptor blocks to be written to disk. This behavior is controlled using JBD2_FEATURE_ASYNC_COMMIT flag. Older kernels/e2fsck should not be able to recover the journal with _ASYNC_COMMIT hence it is made incompat. The commit header has been extended to hold the checksum along with the type of the checksum. For recovery in pass scan checksums are verified to ensure the sanity and completeness(in case of _ASYNC_COMMIT) of every transaction. Signed-off-by: Andreas Dilger <adilger@clusterfs.com> Signed-off-by: Girish Shilamkar <girish@clusterfs.com> Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/ext4.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6a4adcae9f9..4f329afe20e 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -89,6 +89,16 @@ When mounting an ext4 filesystem, the following option are accepted:
extents ext4 will use extents to address file data. The
file system will no longer be mountable by ext3.
+journal_checksum Enable checksumming of the journal transactions.
+ This will allow the recovery code in e2fsck and the
+ kernel to detect corruption in the kernel. It is a
+ compatible change and will be ignored by older kernels.
+
+journal_async_commit Commit block can be written to disk without waiting
+ for descriptor blocks. If enabled older kernels cannot
+ mount the device. This will enable 'journal_checksum'
+ internally.
+
journal=update Update the ext4 file system's journal to the current
format.