Re: [Qemu-devel] [PATCH 0/3] block: block-backup live backup command

[Paolo Bonzini]

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Il 23/04/2013 18:49, Eric Blake ha scritto:
> Based on today's phone call, it sounds like this would mean adding 
> optional parameters to the QMP command.  We already did that for 
> drive-mirror (1.4 has more parameters than 1.3), but without a way
> to introspect when those parameters are available, the new
> parameters aren't quite as useful.  So we don't repeat that
> mistake, we need to decide whether this should still go into 1.5
> with a plan of adding parameters for 1.6, or whether we should add
> a counterpart query-* command that makes it easy to determine how
> much of block-backup is supported, or [your suggestion here]....

... libvirt can omit the optional parameters if they match the default
and just try executing the command.  If it gets an error, it just
reports it.

That is, instead of

     dictionary = json_object_new()
     if (has_capability)
         add argument to JSON dictionary
     else if (argument != default)
         return error

     send JSON dictionary via QMP

do this

     dictionary = json_object_new()
     if (argument != default)
         add argument to JSON dictionary
     send JSON dictionary via QMP

Paolo
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