Re: [PATCH v4] doc: Add alternate trim/zero limits
On 05/03/2018 10:55 AM, Eric Blake wrote:
for BLOCK_STATUS, when we use it in some copying process, it's good to
query large region, to be able to use fast path in case of zero area
(I don't remember, did we finally allowed last chunk of BLOCK_STATUS
to exceed requested region?)
We talked about that. It is NOT currently worded in the spec that way,
but I think the qemu implementation (which is the only known
implementation of BLOCK_STATUS right now) will tolerate it, so now would
be a good time to wordsmith that addition into the standard.
Clarification: the qemu client implementation will tolerate a server
that does that, although qemu as the server does not currently do that.
The idea is that if we want to allow servers to do that, then portable
clients need to be prepared for it to happen, and the longer we go
without documenting that a server may send an overlarge final extent,
the more likely that a client will be implemented that chokes on such a
server, making it harder to add to the spec at a later date.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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