On Sun, 26 Sep 1999 16:42:05 +0200 
 Manuel Bouyer <bouyer@antioche.lip6.fr> wrote:

 > This could also help with tagget command queuing, where tagged commands need
 > to have some ordering information to keep filesystem consistency.

...this is a whole other discussion, but...

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.

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>