I believe the point I was making is that our only current expectation is
simple tag, which is unordered.
> aybe the generator of tags (block layer, user process through sg, etc)
> should also set the tag attribute of the task, as per SAM-3. Most
> often (as currently implicitly) this would be a Simple task attribute.
> Why not the block layer borrow the idea from SAM-3, I see IDE only
> coming closer to SCSI...
> This way there'd be no need for explicit barriers. They can be
> implemented through Ordered and Head of Queue Tasks, everything else
> is Simple attribute task (IO scheduler can play with those as it
> This would provide for a more general basis the whole game (IO
> scheduling, TCQ, IO barriers, etc).
That would be rather the wrong approach. As the layers move up from the
physical hardware, the level of abstraction becomes greater, so the current
proposal is (descending the abstractions):
journal transaction->REQ_BARRIER->cache synchronise (ide) or ordered tag (scsi)
Most of the implementation is in ll_rw_blk.c if you want to take a look
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