Re: Merging relayfs?

[Karim Yaghmour <karim@opersys.com>]

Tom Zanussi wrote:
> In userspace, the sub-buffer reading loop looks at the commit value in
> the sub-buffer, and if it matches (sub-buffer size - padding), the
> buffer has been completely written and can be saved, otherwise it's
> not yet complete and is checked again the next time around.  This way,
> there's no need for a deliver() callback, the relay_commit() is
> replaced with the increment of the reserved commit value, the arrays
> aren't needed and you get the same result in the end in a much simpler
> way, IMHO.

Actually this has a much greater potential of loosing buffers because
we have to poll the buffer for completion. Seen another way, the kernel-
side has got to wait until the user-side has "figured out" that it needs
to commit content to disk. As it was originally, it was relatively
straightforward to dertermine why data was lost: ok, we've signaled it
from kernel space, but the daemon never flushed it out. Without commit/
deliver, things are much less clear, and I still miss what gain we
are making by removing them.

I would very much like to see the commit/deliver functionality back.
Such mechanisms are required for any sane producer-consumer model.

Karim
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