Il 19/12/2013 16:40, Michael S. Tsirkin ha scritto: > On Thu, Dec 19, 2013 at 04:31:41PM +0100, Paolo Bonzini wrote: >> Il 19/12/2013 15:40, Michael S. Tsirkin ha scritto: >>> 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? >> >> Because all properties are associated to a name. In the case of a >> memory device, the name could be "size" or "id". When requesting the >> id, QEMU will use visit_type_str. When requesting the size, QEMU will >> use visit_type_size. Different functions are called, and the different >> functions accept different input. > > QEMU can do this, but if you want a frontend with QMP as backend, > it won't. > So you end up re-implementing this logic in all frontends: > instead of just passing on properties they need to know > where 1G is a number and where it's a name.
You have schema introspection that lets you know if a property is an int or a size. OptsVisitor chose to accept 1G, but this absolutely need not be universal. Human interfaces must not be designed according to QEMU's own whims. Another front-end may want to differentiate 1GB from 1GiB, a graphical front-end may want to present different widgets; they can do it because they see "size" in the schema but in any case the "final" communication to QEMU via QMP will be an int. Paolo
