Re: [Qemu-devel] [PATCH] qapi: add 'query-target' command to return target arch/bit size

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Aug 20, 2012 at 04:48:24PM -0500, Anthony Liguori wrote:
> "Daniel P. Berrange" <berrange@redhat.com> writes:
> 
> > From: "Daniel P. Berrange" <berrange@redhat.com>
> >
> > Add a 'query-target' QAPI command to allow management applications
> > to determine what target architecture a QEMU binary is emulating
> > without having to parse the binary name or -help output
> >
> >   $ qmp-shell -p /tmp/qemu
> >   (QEMU) query-target
> >   {   u'return': {   u'arch': u'x86_64', u'bits': 64}}
> 
> "bits" is really ambiguous.  What it means in QEMU (specifically the
> value you are returning) is probably not what you expect it to mean.

My intent was to indicate the pointer word size for the architecture.
eg 64 for x86_64, ppc64, etc, and 32 and i686, ppc, etc. Probably
should have called it 'wordsize' or something like that

> We're going to most likely fix TARGET_PHYS_ADDR_BITS to 64 real soon.

Hmm, when I looked at the header in my checkout it already
*is* 64 or 32 as I'd expect for the architecture in question.

$ grep PHYS_ADDR_BITS */config-target.mak
alpha-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
arm-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
cris-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
i386-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
lm32-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
m68k-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
microblazeel-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
microblaze-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
mips64el-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
mips64-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
mipsel-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
mips-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
ppc64-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
ppcemb-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
ppc-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
s390x-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
sh4eb-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
sh4-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
sparc64-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
sparc-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
x86_64-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=64
xtensaeb-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32
xtensa-softmmu/config-target.mak:TARGET_PHYS_ADDR_BITS=32

> Why did you include this field?  What information are you looking to get
> from QEMU and what decisions do you plan to make with it?

When libvirt reports the host capabilities it includes the
architecture name and wordsize, amongst other things:

  # virsh capabilities
  ....snip...
  <guest>
    <os_type>hvm</os_type>
    <arch name='arm'>
      <wordsize>32</wordsize>
      <emulator>/bin/qemu-system-arm</emulator>
  ...

Currently we just have a table of arch name -> wordsize mapping
data in libvirt. I figured if I was adding a 'query-target' command
to QEMU, we might as well include this info too. It is not critical
though if you'd rather we omitted it though.

Regards,
Daniel
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