Re: [Qemu-devel] [PATCH v2] doc: Add NBD_CMD_BLOCK_STATUS extension

[Eric Blake <eblake@redhat.com>]

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On 04/13/2016 06:38 AM, Pavel Borzenkov wrote:
>> I'm also starting to think that it is worth FIRST documenting an
>> extension for advertising block sizes, so that we can then couch
>> BLOCK_STATUS in those terms (a server MUST NOT subdivide status into
>> finer granularity than the advertised block sizes).
> 
> Why do you need to operate with blocks instead of list of extents?

It's still a list of extents, just that having a definition of block
sizes means that we can then require that the list of extents will not
be subdivided smaller than a particular block size (so the client
doesn't have to worry about a server overwhelming it with extents
covering 1 byte each).

> What benefits will this approach provide for a client or a server?
> 
> Are you still working on the spec? I can update the patch with
> information about server-side limit/beyond request's length replies and
> post v3, so that things keep moving forward.

You're welcome to post a v3, if you don't want to wait for me to get
around to it.  There's a lot going on in the spec right now, and I'm
hoping to help flush some of the pending patches first.


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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