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

[Eric Blake]

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.

> 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).

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

signature.asc
Description: OpenPGP digital signature