> FUA is a per-command bit. I haven't gone back and read the
> spec, but I believe you can treat it as a "force write-through
> cache" operation. I'm not sure what the effect on other
> drive queued  (tagged) commands are.
> 
> A FUA bit should probably reflect the (inverse) setting of B_ASYNC.
> Again, *if* you have the drive set to a writeback policy.

Probably regardless of how the drive is set; it sounds like it's a
safe thing to always set for non-async ops (but then, a SCSI gooroo I
am not 8-).

Then there's the whole question of how something like this would
interact with e.g. the 'soft updates' code, which manages buffer
dependencies in the kernel.  I suppose that some of the issues raised
could be dealt with via properly-tagged commands, but it sounds like
additional thought may be needed...


cgd