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

["Denis V. Lunev" <den@openvz.org>]

On 04/04/2016 10:58 PM, Alex Bligh wrote:
> Eric,
>
>> Nothing requires the two uses to report at the same granularity.  THe
>> NBD_REPLY_TYPE_BLOCK_STATUS allows the server to divide into descriptors
>> as it sees fit (so it could report holes at a 4k granularity, but
>> dirtiness only at a 64k granularity) - all that matters is that when all
>> the descriptors have been sent, they total up to the length of the
>> original client request.  So by itself, granularity does not require
>> another command.
> Sure, but given you can't report dirtiness without also reporting
> allocation, if they are are at different blocksize I'd rather they
> were in different commands, because otherwise the code to report
> block size needs to work at two different granularities.
>
'dirty' could come after the data was 'trimmed' from the region!
thus we could have dirty unallocated data.

>> At this point, I was just trying to rebase the proposal as originally
>> made by Denis and Pavel; perhaps they will have more insight on how they
>> envisioned using the command, or on whether we should try harder to make
>> this more of a two-way protocol (where the client can tell the server
>> when to mark something as clean, or when to start tracking whether
>> something is dirty).
> I'm not sure it needs to be a two way protocol (see my strawman) but
> I'd like to know it's at least possibly useful.
>
> --
> Alex Bligh
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