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Re: [libvirt] [PATCH] qemu: support qmp on RHEL/CentOS qemu



On 01/25/2012 11:36 PM, Eric Blake wrote:
I'm getting tired of remembering to backport RHEL-specific
patches when building upstream libvirt on RHEL 6.x or CentOS.
All the affected versions of RHEL qemu-kvm have backported
enough patches to a) make JSON useful, and b) modify the
-help text to mention libvirt as the preferred interface;


Eww. That's almost as hackish as ... well ... as using help output to .... Oh, never mind :-)

(seriously, this seems just as reliable as any of the other stuff - I seriously doubt anyone is going to just stick the string "libvirt" into the help of an old version of qemu just for the fun of it)


Assuming that make check passed (and since it's coming from you, I'm sure it did :-), ACK.

which means this string in the help output is a reliable
indicator that we can outsmart a strict version check,
even when upstream qemu 0.12 lacked the needed features.

* src/qemu/qemu_capabilities.c (qemuCapsComputeCmdFlags):
Recognize particular help string present when enough features were
backported to be worth using JSON.
* tests/qemuhelptest.c (mymain): Update tests accordingly.
---
  src/qemu/qemu_capabilities.c |   17 +++++++++++++----
  tests/qemuhelptest.c         |    6 ++++++
  2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 54757fc..c4bad6f 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1104,7 +1104,8 @@ qemuCapsComputeCmdFlags(const char *help,
      if (strstr(help, "-netdev")) {
          /* Disable -netdev on 0.12 since although it exists,
           * the corresponding netdev_add/remove monitor commands
-         * do not, and we need them to be able todo hotplug */
+         * do not, and we need them to be able to do hotplug.
+         * But see below about RHEL build. */
          if (version>= 13000)
              qemuCapsSet(flags, QEMU_CAPS_NETDEV);
      }
@@ -1169,12 +1170,20 @@ qemuCapsComputeCmdFlags(const char *help,
      /* While JSON mode was available in 0.12.0, it was too
       * incomplete to contemplate using. The 0.13.0 release
       * is good enough to use, even though it lacks one or
-     * two features. The benefits of JSON mode now outweigh
-     * the downside.
+     * two features. This is also true of versions of qemu
+     * built for RHEL, labeled 0.12.1, but with extra text
+     * in the help output that mentions that features were
+     * backported for libvirt. The benefits of JSON mode now
+     * outweigh the downside.
       */
  #if HAVE_YAJL
-     if (version>= 13000)
+    if (version>= 13000) {
          qemuCapsSet(flags, QEMU_CAPS_MONITOR_JSON);
+    } else if (version>= 12000&&
+               strstr(help, "libvirt")) {
+        qemuCapsSet(flags, QEMU_CAPS_MONITOR_JSON);
+        qemuCapsSet(flags, QEMU_CAPS_NETDEV);
+    }
  #endif

      if (version>= 13000)
diff --git a/tests/qemuhelptest.c b/tests/qemuhelptest.c
index 8802271..5ad55bc 100644
--- a/tests/qemuhelptest.c
+++ b/tests/qemuhelptest.c
@@ -354,9 +354,11 @@ mymain(void)
              QEMU_CAPS_MIGRATE_QEMU_UNIX,
              QEMU_CAPS_CHARDEV,
              QEMU_CAPS_ENABLE_KVM,
+            QEMU_CAPS_MONITOR_JSON,
              QEMU_CAPS_BALLOON,
              QEMU_CAPS_DEVICE,
              QEMU_CAPS_SMP_TOPOLOGY,
+            QEMU_CAPS_NETDEV,
              QEMU_CAPS_RTC,
              QEMU_CAPS_VHOST_NET,
              QEMU_CAPS_NO_KVM_PIT,
@@ -503,9 +505,11 @@ mymain(void)
              QEMU_CAPS_MIGRATE_QEMU_UNIX,
              QEMU_CAPS_CHARDEV,
              QEMU_CAPS_ENABLE_KVM,
+            QEMU_CAPS_MONITOR_JSON,
              QEMU_CAPS_BALLOON,
              QEMU_CAPS_DEVICE,
              QEMU_CAPS_SMP_TOPOLOGY,
+            QEMU_CAPS_NETDEV,
              QEMU_CAPS_RTC,
              QEMU_CAPS_VHOST_NET,
              QEMU_CAPS_NO_KVM_PIT,
@@ -559,8 +563,10 @@ mymain(void)
              QEMU_CAPS_CHARDEV,
              QEMU_CAPS_ENABLE_KVM,
              QEMU_CAPS_BALLOON,
+            QEMU_CAPS_MONITOR_JSON,
              QEMU_CAPS_DEVICE,
              QEMU_CAPS_SMP_TOPOLOGY,
+            QEMU_CAPS_NETDEV,
              QEMU_CAPS_RTC,
              QEMU_CAPS_VHOST_NET,
              QEMU_CAPS_NO_KVM_PIT,


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