> 
> > Solaris has a B_ORDERED flag which is a hint specifically for this type
> > of thing.
> > 
> > Basically, metadata writes (and any other writes that need to be ordered)
> > would set B_ORDERED, and this would affect disksort() (for disks which
> > don't supported tagged commands) and the type of tag used (for disks that do).
> > 
> > A B_URGENT (Head-Of-Queue tag) flag might also be useful.
> 
> I don't believe that any queue types other than simple queue are used,
> primarily due to buggy implementations of other tag types in target
> devices.  You must be thinking of some other OS.

Solaris uses FLAG_STAG, yes. Kleiman originally wanted B_ORDERED to be
propagated to the driver so that a FLAG_OTAG would then be used to force
all the previous STAG operations out. I guess this didn't get followed up
on.

Buggy implementations in tag devices? Aw, Ed, come on... Sun always
demands custom f/w for all supported devices. You'd think they could get
the tag stuff right then....