qemu: Add support for iothreads

Add a new capability to ensure the iothreads feature exists for the qemu
emulator being run - requires the "query-iothreads" QMP command. Using the
domain XML add correspoding command argument in order to generate the
threads. The iothreads will use a name space "iothread#" where, the
future patch to add support for using an iothread to a disk definition to
merely define which of the available threads to use.

Add tests to ensure the xml/argv processing is correct.  Note that no
change was made to qemuargv2xmltest.c as processing the -object element
would require knowing more than just iothreads.

src/qemu/qemu_capabilities.c

@@ -268,6 +268,7 @@ VIR_ENUM_IMPL(virQEMUCaps, QEMU_CAPS_LAST,
               "rtc-reset-reinjection",
 
               "splash-timeout", /* 175 */
+              "iothread",
     );
 
 
@@ -1493,6 +1494,7 @@ struct virQEMUCapsStringFlags virQEMUCapsObjectTypes[] = {
     { "memory-backend-ram", QEMU_CAPS_OBJECT_MEMORY_RAM },
     { "memory-backend-file", QEMU_CAPS_OBJECT_MEMORY_FILE },
     { "usb-audio", QEMU_CAPS_OBJECT_USB_AUDIO },
+    { "iothread", QEMU_CAPS_OBJECT_IOTHREAD},
 };
 
 static struct virQEMUCapsStringFlags virQEMUCapsObjectPropsVirtioBlk[] = {

src/qemu/qemu_capabilities.h

@@ -215,6 +215,7 @@ typedef enum {
     QEMU_CAPS_OBJECT_USB_AUDIO   = 173, /* usb-audio device support */
     QEMU_CAPS_RTC_RESET_REINJECTION = 174, /* rtc-reset-reinjection monitor command */
     QEMU_CAPS_SPLASH_TIMEOUT     = 175, /* -boot splash-time */
+    QEMU_CAPS_OBJECT_IOTHREAD    = 176, /* -object iothread */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 } virQEMUCapsFlags;

src/qemu/qemu_command.c

@@ -7543,6 +7543,19 @@ qemuBuildCommandLine(virConnectPtr conn,
     virCommandAddArg(cmd, smp);
     VIR_FREE(smp);
 
+    if (def->iothreads > 0 &&
+        virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_IOTHREAD)) {
+        /* Create named iothread objects starting with 1. These may be used
+         * by a disk definition which will associate to an iothread by
+         * supplying a value of 1 up to the number of iothreads available
+         * (since 0 would indicate to not use the feature).
+         */
+        for (i = 1; i <= def->iothreads; i++) {
+            virCommandAddArg(cmd, "-object");
+            virCommandAddArgFormat(cmd, "iothread,id=iothread%zu", i);
+        }
+    }
+
     if (def->cpu && def->cpu->ncells)
         if (qemuBuildNumaArgStr(cfg, def, cmd, qemuCaps) < 0)
             goto error;

tests/qemuxml2argvdata/qemuxml2argv-iothreads.args

+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M \
+pc -m 214 -smp 2 \
+-object iothread,id=iothread1 \
+-object iothread,id=iothread2 \
+-nographic -monitor \
+unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb -hda \
+/dev/HostVG/QEMUGuest1 -net none -serial none -parallel none

tests/qemuxml2argvdata/qemuxml2argv-iothreads.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>2</vcpu>
+  <iothreads>2</iothreads>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu</emulator>
+    <disk type='block' device='disk'>
+      <driver name='qemu' type='raw'/>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <memballoon model='none'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -1185,6 +1185,8 @@ mymain(void)
 
     DO_TEST("smp", QEMU_CAPS_SMP_TOPOLOGY);
 
+    DO_TEST("iothreads", QEMU_CAPS_OBJECT_IOTHREAD);
+
     DO_TEST("cpu-topology1", QEMU_CAPS_SMP_TOPOLOGY);
     DO_TEST("cpu-topology2", QEMU_CAPS_SMP_TOPOLOGY);
     DO_TEST("cpu-topology3", NONE);

tests/qemuxml2xmltest.c

@@ -301,6 +301,7 @@ mymain(void)
     DO_TEST("cputune-zero-shares");
 
     DO_TEST("smp");
+    DO_TEST("iothreads");
     DO_TEST("lease");
     DO_TEST("event_idx");
     DO_TEST("vhost_queues");