Re: Exposing FUA as alternative to DIOCCACHESYNC for WAPBL

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> It needs to do this [flush disc cache after committing journal] because 
> it needs to make sure that journal data are saved before we save the 
> journal commit block.
So the point is to force an order (data before commit block).

> Implicitly, the pre-commit flush also makes sure that all asynchronously 
> written metadata updates are written to the media, before the commit makes
> them impossible to replay.
So the point is do force an order (metadata before journal).

> Even SCSI ORDERED tags wouldn't help to avoid the need for cache flushes.
So why that if the point of the cache flushes is to ensure an order?