I've been following the thread, I hope I haven't missed anything fundamental.
A better long term solution is to have ordered tags work as designed. It's
not broken by design is it, just implementation?
I have a standing offer from at least one engineer to make firmware changes
to the drives if it makes Linux work better. So a reasonable plan is: first
know what's ideal, second ask for it. Coupled with that, we'd need a way of
identifying drives that don't work in the ideal way, and require a fallback.
In my opinion, the only correct behavior is a write barrier that completes
when data is on the platter, and that does this even when write-back is
enabled. Surely this is not rocket science at the disk firmware level. Is
this or is this not the way ordered tags were supposed to work?
> Clearly, there would also have to be a mechanism to flush the cache on
> unmount, so if this were done by ioctl, would you prefer that the filesystem
> be in charge of flushing the cache on barrier writes, or would you like the sd
> device to do it transparently?
The filesystem should just say 'this request is a write barrier' and the
lower layers, whether that's scsi or bio, should do what's necessary to make
it come true.
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