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[Xen-devel] RING_FULL() equivalent for responses?


during review of my qemu pvusb backend patch Anthony raised the
question why my backend doesn't check for the ring being full before

I've checked several existing backends and none of them is doing this
test. To be precise: There is no macro to test this condition as
RING_FULL() is doing this kind of test for the request ring only.

A frontend generating lots of requests might be slow dequeueing the
responses so I guess it could happen that the response ring will
become full while some requests are still active. I know that at
least most of the frontends won't issue another request as long as
RING_SIZE() responses are outstanding, but I'm not aware of any
specification making this behavior mandatory.

As the result of ignoring a full response ring will affect the domU
running the frontend only, I don't think this is a security issue, but
"only" one of correctness.



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