qemu: domain: Store and update 'fdsetindex' across libvirtd restarts

While 'add-fd' qmp command gives the possibility to find an unused fdset
ID when hot-adding fdsets, such usage is extremely inconvenient.

This patch allows us to track the used fdset id so that we can avoid the
need to check results and thus employ simpler code flow when hot-adding
devices which use FD passing.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_domain.c

@@ -2372,6 +2372,8 @@ qemuDomainObjPrivateXMLFormat(virBuffer *buf,
     if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV))
         virBufferAsprintf(buf, "<nodename index='%llu'/>\n", priv->nodenameindex);
 
+    virBufferAsprintf(buf, "<fdset index='%u'/>\n", priv->fdsetindex);
+
     if (priv->memPrealloc)
         virBufferAddLit(buf, "<memPrealloc/>\n");
 
@@ -3106,6 +3108,9 @@ qemuDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt,
         return -1;
     }
 
+    if (virXPathUInt("string(./fdset/@index)", ctxt, &priv->fdsetindex) == 0)
+        priv->fdsetindexParsed = true;
+
     priv->memPrealloc = virXPathBoolean("boolean(./memPrealloc)", ctxt) == 1;
 
     if (virXPathULongLong("string(./originalMemlock)",

src/qemu/qemu_domain.h

@@ -204,8 +204,9 @@ struct _qemuDomainObjPrivate {
     /* counter for generating node names for qemu disks */
     unsigned long long nodenameindex;
 
-    /* counter for generating IDs of fdsets - only relevant during startup */
+    /* counter for generating IDs of fdsets */
     unsigned int fdsetindex;
+    bool fdsetindexParsed;
 
     /* qemuProcessStartCPUs stores the reason for starting vCPUs here for the
      * RESUME event handler to use it */

src/qemu/qemu_process.c

@@ -2265,6 +2265,34 @@ qemuRefreshPRManagerState(virQEMUDriver *driver,
 }
 
 
+static int
+qemuProcessRefreshFdsetIndex(virDomainObj *vm)
+{
+    qemuDomainObjPrivate *priv = vm->privateData;
+    g_autoptr(qemuMonitorFdsets) fdsets = NULL;
+    size_t i;
+    int rc;
+
+    /* if the previous index was in the status XML we don't need to update it */
+    if (priv->fdsetindexParsed)
+        return 0;
+
+    qemuDomainObjEnterMonitor(priv->driver, vm);
+    rc = qemuMonitorQueryFdsets(priv->mon, &fdsets);
+    qemuDomainObjExitMonitor(vm);
+
+    if (rc < 0)
+        return -1;
+
+    for (i = 0; i < fdsets->nfdsets; i++) {
+        if (fdsets->fdsets[i].id >= priv->fdsetindex)
+            priv->fdsetindex = fdsets->fdsets[i].id + 1;
+    }
+
+    return 0;
+}
+
+
 static void
 qemuRefreshRTC(virQEMUDriver *driver,
                virDomainObj *vm)
@@ -8928,6 +8956,9 @@ qemuProcessReconnect(void *opaque)
     if (qemuRefreshPRManagerState(driver, obj) < 0)
         goto error;
 
+    if (qemuProcessRefreshFdsetIndex(obj) < 0)
+        goto error;
+
     qemuProcessReconnectCheckMemAliasOrderMismatch(obj);
 
     if (qemuConnectAgent(driver, obj) < 0)

tests/qemustatusxml2xmldata/backup-pull-in.xml

@@ -234,6 +234,7 @@
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
   <nodename index='0'/>
+  <fdset index='0'/>
   <blockjobs active='yes'>
     <blockjob name='backup-vda-libvirt-3-format' type='backup' state='running' jobflags='0x0'>
       <disk dst='vda'/>

tests/qemustatusxml2xmldata/blockjob-blockdev-in.xml

@@ -233,6 +233,7 @@
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
   <nodename index='0'/>
+  <fdset index='0'/>
   <blockjobs active='yes'>
     <blockjob name='broken-test' type='broken' state='ready' brokentype='commit'/>
     <blockjob name='commit-vdc-libvirt-9-format' type='commit' state='running' jobflags='0x0'>

tests/qemustatusxml2xmldata/blockjob-mirror-in.xml

@@ -22,6 +22,7 @@
   <libDir path='/tmp'/>
   <channelTargetDir path='/tmp/channel'/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='yes'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='qemu' id='1'>

tests/qemustatusxml2xmldata/migration-in-params-in.xml

@@ -256,6 +256,7 @@
   <channelTargetDir path='/var/lib/libvirt/qemu/channel/target/domain-1-nest'/>
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='1'>

tests/qemustatusxml2xmldata/migration-out-nbd-bitmaps-in.xml

@@ -343,6 +343,7 @@
   <rememberOwner/>
   <allowReboot value='yes'/>
   <nodename index='3'/>
+  <fdset index='0'/>
   <blockjobs active='yes'>
     <blockjob name='drive-virtio-disk0' type='copy' state='ready' jobflags='0x0'>
       <disk dst='vda'/>

tests/qemustatusxml2xmldata/migration-out-nbd-out.xml

@@ -259,6 +259,7 @@
   <channelTargetDir path='/var/lib/libvirt/qemu/channel/target/domain-4-upstream'/>
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='4'>

tests/qemustatusxml2xmldata/migration-out-nbd-tls-out.xml

@@ -288,6 +288,7 @@
   <channelTargetDir path='/var/lib/libvirt/qemu/channel/target/domain-3-upstream'/>
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='3'>

tests/qemustatusxml2xmldata/migration-out-params-in.xml

@@ -270,6 +270,7 @@
   <channelTargetDir path='/var/lib/libvirt/qemu/channel/target/domain-7-nest'/>
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='7'>

tests/qemustatusxml2xmldata/modern-in.xml

@@ -261,6 +261,7 @@
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
   <nodename index='123'/>
+  <fdset index='321'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='1'>

tests/qemustatusxml2xmldata/upgrade-out.xml

@@ -258,6 +258,7 @@
   <channelTargetDir path='/var/lib/libvirt/qemu/channel/target/domain-1-upstream'/>
   <chardevStdioLogd/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='1'>

tests/qemustatusxml2xmldata/vcpus-multi-in.xml

@@ -308,6 +308,7 @@
   <libDir path='/tmp'/>
   <channelTargetDir path='/tmp/channel'/>
   <allowReboot value='yes'/>
+  <fdset index='0'/>
   <blockjobs active='no'/>
   <agentTimeout>-2</agentTimeout>
   <domain type='kvm' id='1729'>