On Wed, Dec 07, 2016 at 12:22:32PM -0800, Sergey Karamov wrote: > Currently data journalling is incompatible with encryption: enabling both > at the same time has never been supported by design, and would result in > unpredictable behavior. However, users are not precluded from turning on > both features simultaneously. This change programmatically replaces data > journaling for encrypted regular files with ordered data journaling mode. > > Background: > Journaling encrypted data has not been supported because it operates on > buffer heads of the page in the page cache. Namely, when the commit > happens, which could be up to five seconds after caching, the commit > thread uses the buffer heads attached to the page to copy the contents of > the page to the journal. With encryption, it would have been required to > keep the bounce buffer with ciphertext for up to the aforementioned five > seconds, since the page cache can only hold plaintext and could not be > used for journaling. Alternatively, it would be required to setup the > journal to initiate a callback at the commit time to perform deferred > encryption - in this case, not only would the data have to be written > twice, but it would also have to be encrypted twice. This level of > complexity was not justified for a mode that in practice is very rarely > used because of the overhead from the data journalling. > > Solution: > If data=journaled has been set as a mount option for a filesystem, or if > journaling is enabled on a regular file, do not perform journaling if the > file is also encrypted, instead fall back to the data=ordered mode for the > file. > > Rationale: > The intent is to allow seamless and proper filesystem operation when > journaling and encryption have both been enabled, and have these two > conflicting features gracefully resolved by the filesystem. > > Signed-off-by: Sergey Karamov <skaramov@xxxxxxxxxx> Applied, thanks. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
