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Re: [Nbd] [PATCH] Swap options and option name



On 04/14/2017 07:46 AM, Wouter Verhelst wrote:
> When trying to reply to a client with certain information, it's useful
> if we don't need to read the whole reply but can handle it by reading
> one option, handling it, reading the next one, etc etc. This requires
> that the server is told which export to deal with before getting the
> option names, however.
> 
> As specified, that isn't the case, so this would require the server to
> read in the whole request before it can start processing it.
> 
> Swap options around to make handling the INFO/GO messages easier to do.

I'm so glad my patches for NBD_OPT_GO didn't make it into qemu 2.9 (due
to be released later this month). It's pretty easy for me to fix them to
accommodate this new order, and they should make it into qemu 2.10.

> 
> Signed-off-by: Wouter Verhelst <w@...112...>
> ---
>  doc/proto.md | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/proto.md b/doc/proto.md
> index 92df086..8712626 100644
> --- a/doc/proto.md
> +++ b/doc/proto.md
> @@ -919,11 +919,11 @@ of the newstyle negotiation.
>  
>      Data (both commands):
>  
> -    - 16 bits, number of information requests
> -    - 16 bits x n - list of `NBD_INFO` information requests
>      - 32 bits, length of name (unsigned); MUST be no larger than the
>        option data length - 6
>      - String: name of the export
> +    - 16 bits, number of information requests
> +    - 16 bits x n - list of `NBD_INFO` information requests
>  

I don't see any drawbacks to this change, and your rationale for
covering the block name first makes sense.  ACK.

>      The client MAY list one or more items of specific information it
>      is seeking in the list of information requests, or it MAY specify
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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