[KVM] Enable IOURING only when it is available on the host (#6399) * [KVM] Disable IOURING by default on agents * Refactor * Remove agent property for iouring * Restore property * Refactor suse check and enable on ubuntu by default * Refactor irrespective of guest OS * Improvement * Logs and new path * Refactor condition to enable iouring * Improve condition * Refactor property check * Improvement * Doc comment * Extend comment * Move method * Add log (cherry picked from commit dc975dff958520234624bf025df5ac7a5072c88d) Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

diff --git a/agent/conf/agent.properties b/agent/conf/agent.properties
index 519b875..e4468a1 100644
--- a/agent/conf/agent.properties
+++ b/agent/conf/agent.properties

@@ -286,5 +286,5 @@
 # Enable manually setting CPU's topology on KVM's VM.
 # enable.manually.setting.cpu.topology.on.kvm.vm=true
 
-# Enable/disable IO driver for Qemu / It's enabled by default on KVM agents
+# Enable/disable IO driver for Qemu (in case it is not set CloudStack can also detect if its supported by qemu)
 # enable.io.uring=true

diff --git a/agent/src/main/java/com/cloud/agent/properties/AgentProperties.java b/agent/src/main/java/com/cloud/agent/properties/AgentProperties.java
index 980c9b0..657876c 100644
--- a/agent/src/main/java/com/cloud/agent/properties/AgentProperties.java
+++ b/agent/src/main/java/com/cloud/agent/properties/AgentProperties.java

@@ -54,13 +54,6 @@
      */
     public static final Property<Boolean> ENABLE_MANUALLY_SETTING_CPU_TOPOLOGY_ON_KVM_VM = new Property<Boolean>("enable.manually.setting.cpu.topology.on.kvm.vm", true);
 
-    /**
-     * Enable manually IO driver on KVM's VM. <br>
-     * Data type: boolean.<br>
-     * Default value: true.
-     */
-    public static final Property<Boolean> ENABLE_IO_URING = new Property<Boolean>("enable.io.uring", true);
-
     public static class Property <T>{
         private final String name;
         private final T defaultValue;

diff --git a/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java b/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java
index 76bc590..02d0dde 100644
--- a/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java
+++ b/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java

@@ -313,6 +313,8 @@
 
     public final static String HOST_CACHE_PATH_PARAMETER = "host.cache.location";
     public final static String CONFIG_DIR = "config";
+    private boolean enableIoUring;
+    private final static String ENABLE_IO_URING_PROPERTY = "enable.io.uring";
 
     public static final String BASH_SCRIPT_PATH = "/bin/bash";
 
@@ -1132,6 +1134,12 @@
             s_logger.trace("Ignoring libvirt error.", e);
         }
 
+        // Enable/disable IO driver for Qemu (in case it is not set CloudStack can also detect if its supported by qemu)
+        // Do not remove - switching it to AgentProperties.Property may require accepting null values for the properties default value
+        String enableIoUringConfig = (String) params.get(ENABLE_IO_URING_PROPERTY);
+        enableIoUring = isIoUringEnabled(enableIoUringConfig);
+        s_logger.info("IO uring driver for Qemu: " + (enableIoUring ? "enabled" : "disabled"));
+
         final String cpuArchOverride = (String)params.get("guest.cpu.arch");
         if (!Strings.isNullOrEmpty(cpuArchOverride)) {
             _guestCpuArch = cpuArchOverride;
@@ -2950,19 +2958,67 @@
     }
 
     /**
+     * Check if IO_URING is supported by qemu
+     */
+    protected boolean isIoUringSupportedByQemu() {
+        s_logger.debug("Checking if iouring is supported");
+        String command = getIoUringCheckCommand();
+        if (org.apache.commons.lang3.StringUtils.isBlank(command)) {
+            s_logger.debug("Could not check iouring support, disabling it");
+            return false;
+        }
+        int exitValue = executeBashScriptAndRetrieveExitValue(command);
+        return exitValue == 0;
+    }
+
+    protected String getIoUringCheckCommand() {
+        String[] qemuPaths = { "/usr/bin/qemu-system-x86_64", "/usr/libexec/qemu-kvm", "/usr/bin/qemu-kvm" };
+        for (String qemuPath : qemuPaths) {
+            File file = new File(qemuPath);
+            if (file.exists()) {
+                String cmd = String.format("ldd %s | grep -Eqe '[[:space:]]liburing\\.so'", qemuPath);
+                s_logger.debug("Using the check command: " + cmd);
+                return cmd;
+            }
+        }
+        return null;
+    }
+
+    /**
      * Set Disk IO Driver, if supported by the Libvirt/Qemu version.
      * IO Driver works for:
      * (i) Qemu >= 5.0;
      * (ii) Libvirt >= 6.3.0
      */
     protected void setDiskIoDriver(DiskDef disk) {
-        if (getHypervisorLibvirtVersion() >= HYPERVISOR_LIBVIRT_VERSION_SUPPORTS_IO_URING
-                && getHypervisorQemuVersion() >= HYPERVISOR_QEMU_VERSION_SUPPORTS_IO_URING
-                && AgentPropertiesFileHandler.getPropertyValue(AgentProperties.ENABLE_IO_URING)) {
+        if (enableIoUring) {
             disk.setIoDriver(DiskDef.IoDriver.IOURING);
         }
     }
 
+    /**
+     * IO_URING supported if the property 'enable.io.uring' is set to true OR it is supported by qemu
+     */
+    private boolean isIoUringEnabled(String enableIoUringConfig) {
+        boolean meetRequirements = getHypervisorLibvirtVersion() >= HYPERVISOR_LIBVIRT_VERSION_SUPPORTS_IO_URING
+                && getHypervisorQemuVersion() >= HYPERVISOR_QEMU_VERSION_SUPPORTS_IO_URING;
+        if (!meetRequirements) {
+            return false;
+        }
+        return enableIoUringConfig != null ?
+                Boolean.parseBoolean(enableIoUringConfig):
+                (isBaseOsUbuntu() || isIoUringSupportedByQemu());
+    }
+
+    private boolean isBaseOsUbuntu() {
+        Map<String, String> versionString = getVersionStrings();
+        String hostKey = "Host.OS";
+        if (MapUtils.isEmpty(versionString) || !versionString.containsKey(hostKey) || versionString.get(hostKey) == null) {
+            return false;
+        }
+        return versionString.get(hostKey).equalsIgnoreCase("ubuntu");
+    }
+
     private KVMPhysicalDisk getPhysicalDiskFromNfsStore(String dataStoreUrl, DataTO data) {
         final String volPath = dataStoreUrl + File.separator + data.getPath();
         final int index = volPath.lastIndexOf("/");
@@ -3826,10 +3882,20 @@
     }
 
     private String executeBashScript(final String script) {
+        return createScript(script).execute();
+    }
+
+    private Script createScript(final String script) {
         final Script command = new Script("/bin/bash", _timeout, s_logger);
         command.add("-c");
         command.add(script);
-        return command.execute();
+        return command;
+    }
+
+    private int executeBashScriptAndRetrieveExitValue(final String script) {
+        Script command = createScript(script);
+        command.execute();
+        return command.getExitValue();
     }
 
     public List<VmNetworkStatsEntry> getVmNetworkStat(Connect conn, String vmName) throws LibvirtException {