journal_incompat_revoke?

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What is the meaning of this ext4 feature?

Can anyone point me to a reference that lays out all possible ext4 features?

matthew.l.merchant@uscg.mil's picture

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Yes, this feature does not seem to be widely known.

Here is how I understand it...

From:

https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout

A revocation block is used to prevent replay of a block in an earlier transaction. This is used to mark blocks that were journalled at one time but are no longer journalled. Typically this happens if a metadata block is freed and re-allocated as a file data block; in this case, a journal replay after the file block was written to disk will cause corruption.

In other words, a revocation block is used to record a list of data blocks in this transaction that supersede any older copies of those data blocks that might still be available in the journal. This can speed up recovery because those older copies do not have to be written out to disk.

Regards,

Dusan Baljevic

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