Re: [Qemu-devel] [PATCH 05/27] qapi: add SIZE type parser to string_input_visitor

[Michael S. Tsirkin]

On Mon, Nov 25, 2013 at 09:43:48AM -0700, Eric Blake wrote:
> On 11/25/2013 09:32 AM, Paolo Bonzini wrote:
> 
> >> Yes please. Firing up a calculator to figure out how much is 1G is not
> >> friendly, neither is firing it up to figure out what did management do
> >> with QMP. It should be a text based interface not a binary one.
> 
> Right now, QMP takes an 'int', which does not allow a suffix.  Libvirt
> prefers passing a value in 'bytes', rather than risking confusion on
> whether a value in G was rounded (up, down? to nearest power of 10 or
> power of 2?).  Unfortunately, yes, that means you need a calculator when
> parsing QMP logs to see whether the 1073741824 passed by libvirt is the
> 1G you had in mind.
> 
> HMP, qtest, and any other decent shell around raw QMP is more than
> welcome to provide human-usable wrappers that takes "1G" as a string and
> turns it into the raw int used by the underlying QMP.  In fact, I
> encourage it.

How will it know 1G is not e.g. an ID?

We can invent rules like "IDs should not start with a number", but these
rules are better enforced in a single place for consistency, and it's
likely too late to enforce that in HMP.

> > This is unfortunately a counter-example to the rule that HMP commands
> > should always be implemented in terms of their QMP counterparts.  I do
> > not believe this is really a problem.  It can be fixed later; for now, I
> > think "perfect is the enemy of good" applies.
> 
> Hey - I just realized that now that we have anonymous unions, we could
> theoretically extend QMP to allow a union between 'int' and 'string' -
> if an 'int' is passed, it is in bytes; if a 'string' is passed, then
> parse it the way HMP would (so the string "1G" would be equivalent to
> the raw int 1073741824).  But I don't know if it will help you (libvirt
> will still prefer to use raw ints in any QMP log you read off of libvirt
> interactions).

Yes, I think that would address the issue.

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