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On Dec 16, 2004, at 10:35 AM, Steven M. Bellovin wrote:

> But under what conditions should higher layers set this flag?

Consider the case of a journaling file system.

Writes to the journal itself would be issued with FUA set.

As buffers described by the journal are flushed to disk, the journal 
might decide it's time to advance the journal's "producer" pointer 
(journal replay being the "consumer").  Before it does that, it would 
issue a synchronize-cache command to the disk to ensure that all of 
that data is, in fact, on disk.  Then it would update the producer 
pointer.

Those are a couple of examples, anyway.

         -- Jason R. Thorpe <thorpej@shagadelic.org>


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