Re: [Qemu-devel] [PATCH 10/19] Add a query-machines command to QMP

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

On Mon, Jun 07, 2010 at 12:07:56PM -0500, Anthony Liguori wrote:
> On 06/07/2010 11:44 AM, Daniel P. Berrange wrote:
> >On Mon, Jun 07, 2010 at 10:13:27AM -0500, Anthony Liguori wrote:
> >   
> >>On 06/07/2010 09:42 AM, Daniel P. Berrange wrote:
> >>     
> >>>Add a new QMP monitor command 'query-machines' to discover what
> >>>machines are defined in the QEMU binary. This is an easily
> >>>parsable replacement for 'qemu -M ?'
> >>>
> >>>     [
> >>>         {
> >>>             "name": "pc-0.13",
> >>>             "description": "Standard PC",
> >>>             "default": 0
> >>>         },
> >>>         {
> >>>             "name": "pc",
> >>>             "description": "Standard PC",
> >>>             "canonical": "pc-0.13",
> >>>             "default": 1
> >>>         },
> >>>         {
> >>>             "name": "pc-0.12",
> >>>             "description": "Standard PC",
> >>>             "default": 0
> >>>         },
> >>>         ....
> >>>     ]
> >>>
> >>>No legacy readline monitor output is provided.
> >>>
> >>>In the future it would be desirable for each machine's QDict to
> >>>also include details of any qdev devices that are included by
> >>>default in the machine type.
> >>>
> >>>Signed-off-by: Daniel P. Berrange<berrange@redhat.com>
> >>>---
> >>>  hw/boards.h |    1 +
> >>>  monitor.c   |    9 +++++++
> >>>  vl.c        |   70
> >>>  +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>>  3 files changed, 80 insertions(+), 0 deletions(-)
> >>>
> >>>diff --git a/hw/boards.h b/hw/boards.h
> >>>index 6f0f0d7..2f6003d 100644
> >>>--- a/hw/boards.h
> >>>+++ b/hw/boards.h
> >>>@@ -32,6 +32,7 @@ typedef struct QEMUMachine {
> >>>  } QEMUMachine;
> >>>
> >>>  int qemu_register_machine(QEMUMachine *m);
> >>>+void do_info_machines(Monitor *mon, QObject **data);
> >>>
> >>>  extern QEMUMachine *current_machine;
> >>>
> >>>diff --git a/monitor.c b/monitor.c
> >>>index f0406e8..b6aa2b4 100644
> >>>--- a/monitor.c
> >>>+++ b/monitor.c
> >>>@@ -55,6 +55,7 @@
> >>>  #include "json-streamer.h"
> >>>  #include "json-parser.h"
> >>>  #include "osdep.h"
> >>>+#include "hw/boards.h"
> >>>
> >>>  //#define DEBUG
> >>>  //#define DEBUG_COMPLETION
> >>>@@ -2449,6 +2450,14 @@ static const mon_cmd_t info_cmds[] = {
> >>>          .mhandler.info_new = do_info_version,
> >>>      },
> >>>      {
> >>>+        .name       = "machines",
> >>>+        .args_type  = "",
> >>>+        .params     = "",
> >>>+        .help       = "show the machine boards",
> >>>+        .user_print = monitor_user_noop,
> >>>+        .mhandler.info_new = do_info_machines,
> >>>+    },
> >>>+    {
> >>>          .name       = "commands",
> >>>          .args_type  = "",
> >>>          .params     = "",
> >>>diff --git a/vl.c b/vl.c
> >>>index 0b38d62..8043fac 100644
> >>>--- a/vl.c
> >>>+++ b/vl.c
> >>>@@ -1537,6 +1537,76 @@ static QEMUMachine *find_default_machine(void)
> >>>      return NULL;
> >>>  }
> >>>
> >>>+
> >>>+/**
> >>>+ * do_info_machines(): Show machine boards
> >>>+ *
> >>>+ * Returns a QList object listing all machine boards
> >>>+ * available with this QEMU target. Each element in
> >>>+ * the list is a QDict object containing the following
> >>>+ * keys
> >>>+ *
> >>>+ *  - "name": short name for the machine board
> >>>+ *  - "description": long description of the board
> >>>+ *  - "alias": name of an alias
> >>>+ *
> >>>+ * Example:
> >>>+ *
> >>>+ *  [
> >>>+ *     {
> >>>+ *       "name": "pc-0.13",
> >>>+ *        "description": "Standard PC",
> >>>+ *        "default": 0
> >>>+ *     },
> >>>+ *     {
> >>>+ *       "name": "pc",
> >>>+ *       "description": "Standard PC",
> >>>+ *       "canonical": "pc-0.13",
> >>>+ *       "default": 1
> >>>+ *     },
> >>>+ *     {
> >>>+ *       "name": "pc-0.12",
> >>>+ *       "description": "Standard PC",
> >>>+ *       "default": 0
> >>>+ *     },
> >>>+ *     ....
> >>>+ *  ]
> >>>+ *
> >>>+ */
> >>>
> >>>       
> >>My only suggestion would be to:
> >>
> >>{ 'default-machine': 'pc',
> >>    'machines': [{
> >>      'name': 'pc',
> >>      'description': 'Standard PC',
> >>    },...]
> >>}
> >>
> >>I'd drop 'canonical' too.  Aliasing is an implementation detail and
> >>should not be exposed via the ABI.
> >>     
> >The alias/canonical mapping is something that libvirt needs to know in
> >order guarentee stable guest ABI for all configs it has.
> >
> >What happens is that an app using libvirt will request a guest config
> >with machine type 'pc',
> 
> Does the guest config encode the machine type?  Does that mean that I 
> can't specify pc-0.12 or pc-0.13?

Yes, the XML lets you specify an explicit machine type yourself.

> Since most guests don't specify an explicit machine, can't libvirt just 
> use pc-<version> and be done with it?

If we make sure the 'default-machine' pointed to the latest version
machine type ('pc-0.13' and not 'pc') we could just hardcode to use
the default machine type whenever we see 'pc' in libvirt. Currently
the 'default-machine' and 'pc' canonicalization are separately varied
in QEMU.

Regards,
Daniel
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