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Re: [libvirt] [PATCHv2 1/2] Optimize machine option to set more options with it.

On 2013年03月27日 23:08, Martin Kletzander wrote:
On 03/15/2013 10:19 AM, Li Zhang wrote:
From: Li Zhang <zhlcindy linux vnet ibm com>

  Currently, -machine option is used only when dump-guest-core is set.

  To use options defined in machine option for newer version of QEMU,
  it needs to use -machine xxx, and to be compatible with older version
  -M, this patch addes QEMU_CAPS_MACHINE_OPT capability for newer version,
  say 1.2.0.

Signed-off-by: Li Zhang <zhlcindy linux vnet ibm com>
  v2 -> v1:
   * Split the patch to 2 parts suggested by Daniel P.Berrange
   * Remove version 1.1 assertion for QEMU_CAPS_MACHINE_OPT

  src/qemu/qemu_capabilities.c |    6 +++++-
  src/qemu/qemu_capabilities.h |    1 +
  src/qemu/qemu_command.c      |   30 +++++++++++++++++++-----------
  tests/qemuxml2argvtest.c     |    6 +++---
  4 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 519d2c5..778e825 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -210,7 +210,8 @@ VIR_ENUM_IMPL(virQEMUCaps, QEMU_CAPS_LAST,
"rng-random", /* 130 */
-              "virtio-ccw"
+              "virtio-ccw",
+              "machine-opt"
struct _virQEMUCaps {
@@ -2442,6 +2443,9 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
virQEMUCapsInitQMPBasic(qemuCaps); + /* machine option is supported for newer version */
+    virQEMUCapsSet(qemuCaps, QEMU_CAPS_MACHINE_OPT);
But this is also supported when we don't probe by QMP.

Ah, okay, it should be set when using help string.

      if (!(archstr = qemuMonitorGetTargetArch(mon)))
          goto cleanup;
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index da06e27..66df556 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -172,6 +172,7 @@ enum virQEMUCapsFlags {
                                             virtio rng */
      QEMU_CAPS_OBJECT_RNG_EGD     = 131, /* EGD protocol daemon for rng */
      QEMU_CAPS_VIRTIO_CCW         = 132, /* -device virtio-*-ccw */
+    QEMU_CAPS_MACHINE_OPT        = 133, /* -machine xxxx*/
QEMU_CAPS_LAST, /* this must always be the last item */
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index dc49d44..c39faf0 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -4941,6 +4941,8 @@ qemuBuildMachineArgStr(virCommandPtr cmd,
                         const virDomainDefPtr def,
                         virQEMUCapsPtr qemuCaps)
+    virBuffer buf = VIR_BUFFER_INITIALIZER;
      /* This should *never* be NULL, since we always provide
       * a machine in the capabilities data for QEMU. So this
       * check is just here as a safety in case the unexpected
@@ -4948,27 +4950,33 @@ qemuBuildMachineArgStr(virCommandPtr cmd,
      if (!def->os.machine)
          return 0;
- if (!def->mem.dump_core) {
+    if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_MACHINE_OPT)) {
This was intentionally done the way you see.  I tried to avoid using
'-machine' for various other qemu implementations (I couldn't find
anywhere that '-machine' is guaranteed on all sorts of implementations).
  This is why the following comment is in place, which you obsoleted, but
haven't removed, so it doesn't make much sense now.
I see. You are right, the comment should be removed.

Also this won't work with implementations where we don't probe by QMP,
but '-machine dump-core=xx' is supported.

Currently, it assumes that 1.2.0 supports QMP and -machine.
As you mentioned, I will add this capability when using help string.
Is it okay to support -machine with 1.1.0 onwards ?

          /* if no parameter to the machine type is needed, we still use
           * '-M' to keep the most of the compatibility with older versions.
          virCommandAddArgList(cmd, "-M", def->os.machine, NULL);
      } else {
-        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_DUMP_GUEST_CORE)) {
-            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                           "%s", _("dump-guest-core is not available "
-                                   " with this QEMU binary"));
-            return -1;
-        }
/* However, in case there is a parameter to be added, we need to
           * use the "-machine" parameter because qemu is not parsing the
           * "-M" correctly */
          virCommandAddArg(cmd, "-machine");
-        virCommandAddArgFormat(cmd,
-                               "%s,dump-guest-core=%s",
-                               def->os.machine,
-                               virDomainMemDumpTypeToString(def->mem.dump_core));
+        virBufferAsprintf(&buf, "%s", def->os.machine);
+        if (def->mem.dump_core) {
+            if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_DUMP_GUEST_CORE)) {
There is also on pre-existing bug in my code which I see now.  When
probing by QMP, we don't set QEMU_CAPS_DUMP_GUEST_CORE flag and hence
report this as unsupported even when the qemu knows this option :(
So it needs to add this capability when using QMP.

However, I believe we have to do some more investigation and rely on
version-specific capabilities only as a last resort.  But because there
is no way to get information about ',usb=off' and more of these are
already in the code and coming, we will probably need to switch to
'-machine' anyway.
Yes, you are right.
Replying to your [2/2] here as well, with what kind of configuration do
you experience such problems?  I see no problems with upstream git QEMU
(reporting itself as version 1.4.50), nor 1.4.0.
Ah, this is a problem on PowerPC.
To compare with PowerPC, X86 doesn't create USB controller in
X86 machine init code in QEMU is as the following:
if (pci_enabled && usb_enabled(false)) {
pci_create_simple(pci_bus, piix3_devfn + 2, "piix3-usb-uhci");

But PowerPC init code in QEMU is as the following:
if (usb_enabled(spapr->has_graphics)) {
pci_create_simple(phb->bus, -1, "pci-ohci");
if (spapr->has_graphics) {

When spapr->has_graphics is true, it will create one USB controller implicitly. But in libvirt, it also creates one USB controller implicitly if no USB controller specified.
So this will cause errors.

I think you can also get errors by hacking X86 QEMU code with usb_enabled(true)

If with ,usb=off, it will get false with (usb_enabled(spapr->has_graphics)).
Then libvirt can use its own controller created implicitly.



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