[PATCH 6/7] qemu: Probe QEMU binary for host CPU

[Jiri Denemark <jdenemar@xxxxxxxxxx>]

Since QEMU and kvm may filter some host CPU features or add efficiently
emulated features, asking QEMU binary for host CPU data provides
better results when we later use the data for building guest CPUs.
---
 src/qemu/qemu_capabilities.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 src/qemu/qemu_capabilities.h |  2 ++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 9440396..d46a059 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -253,6 +253,7 @@ struct _virQEMUCaps {
 
     size_t ncpuDefinitions;
     char **cpuDefinitions;
+    virCPUDefPtr hostCPU;
 
     size_t nmachineTypes;
     char **machineTypes;
@@ -1757,6 +1758,9 @@ virQEMUCapsPtr virQEMUCapsNewCopy(virQEMUCapsPtr qemuCaps)
             goto error;
     }
 
+    if (!(ret->hostCPU = virCPUDefCopy(qemuCaps->hostCPU)))
+        goto error;
+
     if (VIR_ALLOC_N(ret->machineTypes, qemuCaps->nmachineTypes) < 0)
         goto error;
     if (VIR_ALLOC_N(ret->machineAliases, qemuCaps->nmachineTypes) < 0)
@@ -1796,6 +1800,7 @@ void virQEMUCapsDispose(void *obj)
         VIR_FREE(qemuCaps->cpuDefinitions[i]);
     }
     VIR_FREE(qemuCaps->cpuDefinitions);
+    virCPUDefFree(qemuCaps->hostCPU);
 
     virBitmapFree(qemuCaps->flags);
 
@@ -2485,7 +2490,6 @@ virQEMUCapsInitQMPCommandNew(const char *binary,
                                "-no-user-config",
                                "-nodefaults",
                                "-nographic",
-                               "-M", "none",
                                "-qmp", monitor,
                                "-pidfile", pidfile,
                                "-daemonize",
@@ -2617,6 +2621,7 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
 
     cmd = virQEMUCapsInitQMPCommandNew(qemuCaps->binary, monarg, pidfile,
                                        runUid, runGid);
+    virCommandAddArgList(cmd, "-M", "none", NULL);
 
     if ((ret = virQEMUCapsInitQMPCommandRun(cmd, qemuCaps->binary, pidfile,
                                             &config, &mon, &pid)) < 0) {
@@ -2679,6 +2684,37 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
     if (virQEMUCapsProbeQMPCommandLine(qemuCaps, mon) < 0)
         goto cleanup;
 
+    if ((qemuCaps->arch == VIR_ARCH_I686 ||
+         qemuCaps->arch == VIR_ARCH_X86_64) &&
+        (virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM) ||
+         virQEMUCapsGet(qemuCaps, QEMU_CAPS_ENABLE_KVM)) &&
+        virQEMUCapsGet(qemuCaps, QEMU_CAPS_CPU_HOST) &&
+        qemuCaps->nmachineTypes) {
+        virQEMUCapsInitQMPCommandAbort(&cmd, &mon, &pid, pidfile);
+
+        VIR_DEBUG("Checking host CPU data provided by %s", qemuCaps->binary);
+        cmd = virQEMUCapsInitQMPCommandNew(qemuCaps->binary, monarg, pidfile,
+                                           runUid, runGid);
+        virCommandAddArgList(cmd, "-cpu", "host", NULL);
+        /* -cpu host gives the same CPU for all machine types so we just
+         * use the first one when probing
+         */
+        virCommandAddArg(cmd, "-machine");
+        virCommandAddArgFormat(cmd, "%s,accel=kvm",
+                               qemuCaps->machineTypes[0]);
+
+        if (virQEMUCapsInitQMPCommandRun(cmd, qemuCaps->binary, pidfile,
+                                         &config, &mon, &pid) < 0)
+            goto cleanup;
+
+        qemuCaps->hostCPU = qemuMonitorGetCPU(mon, qemuCaps->arch);
+        if (qemuCaps->hostCPU) {
+            char *cpu = virCPUDefFormat(qemuCaps->hostCPU, 0);
+            VIR_DEBUG("Host CPU reported by %s: %s", qemuCaps->binary, cpu);
+            VIR_FREE(cpu);
+        }
+    }
+
     ret = 0;
 
 cleanup:
@@ -2858,3 +2894,9 @@ virQEMUCapsUsedQMP(virQEMUCapsPtr qemuCaps)
 {
     return qemuCaps->usedQMP;
 }
+
+virCPUDefPtr
+virQEMUCapsGetHostCPU(virQEMUCapsPtr qemuCaps)
+{
+    return qemuCaps->hostCPU;
+}
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index f5f685d..e7774a3 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -272,4 +272,6 @@ int virQEMUCapsParseDeviceStr(virQEMUCapsPtr qemuCaps, const char *str);
 VIR_ENUM_DECL(virQEMUCaps);
 
 bool virQEMUCapsUsedQMP(virQEMUCapsPtr qemuCaps);
+virCPUDefPtr virQEMUCapsGetHostCPU(virQEMUCapsPtr qemuCaps);
+
 #endif /* __QEMU_CAPABILITIES_H__*/
-- 
1.8.3.2

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