On 05/02/2016 09:48 PM, Dan Williams wrote:
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quoted

And then it keeps broken the aligned buffered writes, which are still
broken after this set.

...identical to the current situation with a traditional disk.

Not true!! please see what I wrote "aligned buffered writes"
If there are no reads involved then there are no errors returned
to application.

quoted

I have by now read the v2 patches. And I think you guys did not yet try
the proper fix for dax_do_io. I think you need to go deeper into the loops
and selectively call bdev_* when error on a specific page copy. No need to
go through direct_IO path at all.

We still reach a point where the minimum granularity of
bdev_direct_access() is larger than a sector, so you end up still
needing to have the application understand how to send a properly
aligned I/O.  The semantics of how to send a properly aligned
direct-I/O are already well understood, so we simply reuse that path.

You are making a mountain out of a mouse. The simple copy of a file
from start (offset ZERO) to end-of-file which is the most common usage
on earth is perfectly aligned and needs not any O_DIRECT and is what is used
everywhere.

quoted

Do you need that I send you a patch to demonstrate what I mean?

I remain skeptical of what you are proposing, but yes, a patch has a
better chance to move the discussion forward.

Sigh! OK
Boaz