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[libvirt] [PATCH] qemu: allow blkstat/blkinfo calls during migration



Originally most of libvirt domain-specific calls were blocking
during a migration.
A new mechanism to allow specific calls (blkstat/blkinfo) to be
executed in such condition has been implemented.
In the long term it'd be desirable to get a more general
solution to mark further APIs as migration safe, without needing
special case code.

 * src/qemu/qemu_migration.c: add some additional job signal
   flags for doing blkstat/blkinfo during a migration
 * src/qemu/qemu_domain.c: add a condition variable that can be
   used to efficiently wait for the migration code to clear the
   signal flag
 * src/qemu/qemu_driver.c: execute blkstat/blkinfo using the
   job signal flags during migration
---
 src/qemu/qemu_domain.c    |    6 +++
 src/qemu/qemu_domain.h    |    9 ++++
 src/qemu/qemu_driver.c    |  103 ++++++++++++++++++++++++++++++++-------------
 src/qemu/qemu_migration.c |   35 +++++++++++++++
 4 files changed, 123 insertions(+), 30 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index c61f9bf..570d65e 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -110,6 +110,11 @@ static void *qemuDomainObjPrivateAlloc(void)
     if (VIR_ALLOC(priv) < 0)
         return NULL;
 
+    if (virCondInit(&priv->signalCond) < 0) {
+        VIR_FREE(priv);
+        return NULL;
+    }
+
     return priv;
 }
 
@@ -122,6 +127,7 @@ static void qemuDomainObjPrivateFree(void *data)
     qemuDomainPCIAddressSetFree(priv->pciaddrs);
     virDomainChrSourceDefFree(priv->monConfig);
     VIR_FREE(priv->vcpupids);
+    ignore_value(virCondDestroy(&priv->signalCond));
 
     /* This should never be non-NULL if we get here, but just in case... */
     if (priv->mon) {
diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index 6d24f53..af513e7 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -47,11 +47,19 @@ enum qemuDomainJobSignals {
     QEMU_JOB_SIGNAL_SUSPEND = 1 << 1, /* Request VM suspend to finish live migration offline */
     QEMU_JOB_SIGNAL_MIGRATE_DOWNTIME = 1 << 2, /* Request migration downtime change */
     QEMU_JOB_SIGNAL_MIGRATE_SPEED = 1 << 3, /* Request migration speed change */
+    QEMU_JOB_SIGNAL_BLKSTAT = 1 << 4, /* Request blkstat during migration */
+    QEMU_JOB_SIGNAL_BLKINFO = 1 << 5, /* Request blkinfo during migration */
 };
 
 struct qemuDomainJobSignalsData {
     unsigned long long migrateDowntime; /* Data for QEMU_JOB_SIGNAL_MIGRATE_DOWNTIME */
     unsigned long migrateBandwidth; /* Data for QEMU_JOB_SIGNAL_MIGRATE_SPEED */
+    char *statDevName; /* Device name used by blkstat calls */
+    virDomainBlockStatsPtr blockStat; /* Block statistics for QEMU_JOB_SIGNAL_BLKSTAT */
+    int statRetCode; /* Return code for the blkstat calls */
+    char *infoDevName; /* Device name used by blkinfo calls */
+    virDomainBlockInfoPtr blockInfo; /* Block information for QEMU_JOB_SIGNAL_BLKINFO */
+    int infoRetCode; /* Return code for the blkinfo calls */
 };
 
 typedef struct _qemuDomainPCIAddressSet qemuDomainPCIAddressSet;
@@ -61,6 +69,7 @@ typedef struct _qemuDomainObjPrivate qemuDomainObjPrivate;
 typedef qemuDomainObjPrivate *qemuDomainObjPrivatePtr;
 struct _qemuDomainObjPrivate {
     virCond jobCond; /* Use in conjunction with main virDomainObjPtr lock */
+    virCond signalCond; /* Use to coordinate the safe queries during migration */
     enum qemuDomainJob jobActive;   /* Currently running job */
     unsigned int jobSignals;        /* Signals for running job */
     struct qemuDomainJobSignalsData jobSignalsData; /* Signal specific data */
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 4f288d3..f7b2cb4 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -5082,15 +5082,6 @@ qemudDomainBlockStats (virDomainPtr dom,
         goto cleanup;
     }
 
-    if (qemuDomainObjBeginJob(vm) < 0)
-        goto cleanup;
-
-    if (!virDomainObjIsActive(vm)) {
-        qemuReportError(VIR_ERR_OPERATION_INVALID,
-                        "%s", _("domain is not running"));
-        goto endjob;
-    }
-
     for (i = 0 ; i < vm->def->ndisks ; i++) {
         if (STREQ(path, vm->def->disks[i]->dst)) {
             disk = vm->def->disks[i];
@@ -5101,29 +5092,57 @@ qemudDomainBlockStats (virDomainPtr dom,
     if (!disk) {
         qemuReportError(VIR_ERR_INVALID_ARG,
                         _("invalid path: %s"), path);
-        goto endjob;
+        goto cleanup;
     }
 
     if (!disk->info.alias) {
         qemuReportError(VIR_ERR_INTERNAL_ERROR,
                         _("missing disk device alias name for %s"), disk->dst);
-        goto endjob;
+        goto cleanup;
     }
 
     priv = vm->privateData;
-    qemuDomainObjEnterMonitor(vm);
-    ret = qemuMonitorGetBlockStatsInfo(priv->mon,
-                                       disk->info.alias,
-                                       &stats->rd_req,
-                                       &stats->rd_bytes,
-                                       &stats->wr_req,
-                                       &stats->wr_bytes,
-                                       &stats->errs);
-    qemuDomainObjExitMonitor(vm);
+    if ((priv->jobActive == QEMU_JOB_MIGRATION_OUT)
+        || (priv->jobActive == QEMU_JOB_SAVE)) {
+        virDomainObjRef(vm);
+        while (priv->jobSignals & QEMU_JOB_SIGNAL_BLKSTAT)
+            ignore_value(virCondWait(&priv->signalCond, &vm->lock));
+
+        priv->jobSignals |= QEMU_JOB_SIGNAL_BLKSTAT;
+        priv->jobSignalsData.statDevName = disk->info.alias;
+        priv->jobSignalsData.blockStat = stats;
+        priv->jobSignalsData.statRetCode = -1;
+
+        while (priv->jobSignals & QEMU_JOB_SIGNAL_BLKSTAT)
+            ignore_value(virCondWait(&priv->signalCond, &vm->lock));
+
+        ret = priv->jobSignalsData.statRetCode;
+        if (virDomainObjUnref(vm) == 0)
+            vm = NULL;
+    } else {
+        if (qemuDomainObjBeginJob(vm) < 0)
+            goto cleanup;
+
+        if (!virDomainObjIsActive(vm)) {
+            qemuReportError(VIR_ERR_OPERATION_INVALID,
+                            "%s", _("domain is not running"));
+            goto endjob;
+        }
+
+        qemuDomainObjEnterMonitor(vm);
+        ret = qemuMonitorGetBlockStatsInfo(priv->mon,
+                                           disk->info.alias,
+                                           &stats->rd_req,
+                                           &stats->rd_bytes,
+                                           &stats->wr_req,
+                                           &stats->wr_bytes,
+                                           &stats->errs);
+        qemuDomainObjExitMonitor(vm);
 
 endjob:
-    if (qemuDomainObjEndJob(vm) == 0)
-        vm = NULL;
+        if (qemuDomainObjEndJob(vm) == 0)
+            vm = NULL;
+    }
 
 cleanup:
     if (vm)
@@ -5527,20 +5546,44 @@ static int qemuDomainGetBlockInfo(virDomainPtr dom,
         format != VIR_STORAGE_FILE_RAW &&
         S_ISBLK(sb.st_mode)) {
         qemuDomainObjPrivatePtr priv = vm->privateData;
-        if (qemuDomainObjBeginJob(vm) < 0)
-            goto cleanup;
-        if (!virDomainObjIsActive(vm))
-            ret = 0;
-        else {
+
+        if ((priv->jobActive == QEMU_JOB_MIGRATION_OUT)
+            || (priv->jobActive == QEMU_JOB_SAVE)) {
+            virDomainObjRef(vm);
+            while (priv->jobSignals & QEMU_JOB_SIGNAL_BLKINFO)
+                ignore_value(virCondWait(&priv->signalCond, &vm->lock));
+
+            priv->jobSignals |= QEMU_JOB_SIGNAL_BLKINFO;
+            priv->jobSignalsData.infoDevName = disk->info.alias;
+            priv->jobSignalsData.blockInfo = info;
+            priv->jobSignalsData.infoRetCode = -1;
+
+            while (priv->jobSignals & QEMU_JOB_SIGNAL_BLKINFO)
+                ignore_value(virCondWait(&priv->signalCond, &vm->lock));
+
+            ret = priv->jobSignalsData.infoRetCode;
+            if (virDomainObjUnref(vm) == 0)
+                vm = NULL;
+        } else {
+            if (qemuDomainObjBeginJob(vm) < 0)
+                goto cleanup;
+
+            if (!virDomainObjIsActive(vm)) {
+                qemuReportError(VIR_ERR_OPERATION_INVALID,
+                                "%s", _("domain is not running"));
+                goto endjob;
+            }
+
             qemuDomainObjEnterMonitor(vm);
             ret = qemuMonitorGetBlockExtent(priv->mon,
                                             disk->info.alias,
                                             &info->allocation);
             qemuDomainObjExitMonitor(vm);
-        }
 
-        if (qemuDomainObjEndJob(vm) == 0)
-            vm = NULL;
+endjob:
+            if (qemuDomainObjEndJob(vm) == 0)
+                vm = NULL;
+        }
     } else {
         ret = 0;
     }
diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index 6738a53..21fdb4c 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -158,6 +158,38 @@ qemuMigrationWaitForCompletion(struct qemud_driver *driver, virDomainObjPtr vm)
                 VIR_WARN0("Unable to set migration speed");
         }
 
+        if (priv->jobSignals & QEMU_JOB_SIGNAL_BLKSTAT) {
+            qemuDomainObjEnterMonitorWithDriver(driver, vm);
+            rc = qemuMonitorGetBlockStatsInfo(priv->mon,
+                                  priv->jobSignalsData.statDevName,
+                                  &priv->jobSignalsData.blockStat->rd_req,
+                                  &priv->jobSignalsData.blockStat->rd_bytes,
+                                  &priv->jobSignalsData.blockStat->wr_req,
+                                  &priv->jobSignalsData.blockStat->wr_bytes,
+                                  &priv->jobSignalsData.blockStat->errs);
+            qemuDomainObjExitMonitorWithDriver(driver, vm);
+
+            priv->jobSignalsData.statRetCode = rc;
+            priv->jobSignals ^= QEMU_JOB_SIGNAL_BLKSTAT;
+
+            if (rc < 0)
+                VIR_WARN0("Unable to get block statistics");
+        }
+
+        if (priv->jobSignals & QEMU_JOB_SIGNAL_BLKINFO) {
+            qemuDomainObjEnterMonitorWithDriver(driver, vm);
+            rc = qemuMonitorGetBlockExtent(priv->mon,
+                               priv->jobSignalsData.infoDevName,
+                               &priv->jobSignalsData.blockInfo->allocation);
+            qemuDomainObjExitMonitorWithDriver(driver, vm);
+
+            priv->jobSignalsData.infoRetCode = rc;
+            priv->jobSignals ^= QEMU_JOB_SIGNAL_BLKINFO;
+
+            if (rc < 0)
+                VIR_WARN0("Unable to get block information");
+        }
+
         /* Repeat check because the job signals might have caused
          * guest to die
          */
@@ -223,6 +255,8 @@ qemuMigrationWaitForCompletion(struct qemud_driver *driver, virDomainObjPtr vm)
             break;
         }
 
+        virCondSignal(&priv->signalCond);
+
         virDomainObjUnlock(vm);
         qemuDriverUnlock(driver);
 
@@ -233,6 +267,7 @@ qemuMigrationWaitForCompletion(struct qemud_driver *driver, virDomainObjPtr vm)
     }
 
 cleanup:
+    virCondBroadcast(&priv->signalCond);
     return ret;
 }
 
-- 
1.7.1


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