qemu: make block io tuning smarter

When blkdeviotune was first committed in 0.9.8, we had the limitation
that setting one value reset all others.  But bytes and iops should
be relatively independent.  Furthermore, setting tuning values on
a live domain followed by dumpxml did not output the new settings.

* src/qemu/qemu_driver.c (qemuDiskPathToAlias): Add parameter, and
update callers.
(qemuDomainSetBlockIoTune): Don't lose previous unrelated
settings.  Make live changes reflect to dumpxml output.
* tools/virsh.pod (blkdeviotune): Update documentation.

src/qemu/qemu_driver.c

@@ -11309,7 +11309,7 @@ cleanup:
 }
 
 static char *
-qemuDiskPathToAlias(virDomainObjPtr vm, const char *path)
+qemuDiskPathToAlias(virDomainObjPtr vm, const char *path, int *idx)
 {
     int i;
     char *ret = NULL;
@@ -11320,6 +11320,8 @@ qemuDiskPathToAlias(virDomainObjPtr vm, const char *path)
         goto cleanup;
 
     disk = vm->def->disks[i];
+    if (idx)
+        *idx = i;
 
     if (disk->type != VIR_DOMAIN_DISK_TYPE_BLOCK &&
         disk->type != VIR_DOMAIN_DISK_TYPE_FILE)
@@ -11361,7 +11363,7 @@ qemuDomainBlockJobImpl(virDomainPtr dom, const char *path, const char *base,
         goto cleanup;
     }
 
-    device = qemuDiskPathToAlias(vm, path);
+    device = qemuDiskPathToAlias(vm, path, NULL);
     if (!device) {
         goto cleanup;
     }
@@ -11529,11 +11531,14 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
     qemuDomainObjPrivatePtr priv;
     virDomainDefPtr persistentDef = NULL;
     virDomainBlockIoTuneInfo info;
+    virDomainBlockIoTuneInfo *oldinfo;
     char uuidstr[VIR_UUID_STRING_BUFLEN];
     const char *device = NULL;
     int ret = -1;
     int i;
     int idx = -1;
+    bool set_bytes = false;
+    bool set_iops = false;
 
     virCheckFlags(VIR_DOMAIN_AFFECT_LIVE |
                   VIR_DOMAIN_AFFECT_CONFIG, -1);
@@ -11564,7 +11569,7 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
         goto cleanup;
     }
 
-    device = qemuDiskPathToAlias(vm, disk);
+    device = qemuDiskPathToAlias(vm, disk, &idx);
     if (!device) {
         goto cleanup;
     }
@@ -11581,21 +11586,27 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
 
         if (STREQ(param->field, VIR_DOMAIN_BLOCK_IOTUNE_TOTAL_BYTES_SEC)) {
             info.total_bytes_sec = param->value.ul;
+            set_bytes = true;
         } else if (STREQ(param->field,
                          VIR_DOMAIN_BLOCK_IOTUNE_READ_BYTES_SEC)) {
             info.read_bytes_sec = param->value.ul;
+            set_bytes = true;
         } else if (STREQ(param->field,
                          VIR_DOMAIN_BLOCK_IOTUNE_WRITE_BYTES_SEC)) {
             info.write_bytes_sec = param->value.ul;
+            set_bytes = true;
         } else if (STREQ(param->field,
                          VIR_DOMAIN_BLOCK_IOTUNE_TOTAL_IOPS_SEC)) {
             info.total_iops_sec = param->value.ul;
+            set_iops = true;
         } else if (STREQ(param->field,
                          VIR_DOMAIN_BLOCK_IOTUNE_READ_IOPS_SEC)) {
             info.read_iops_sec = param->value.ul;
+            set_iops = true;
         } else if (STREQ(param->field,
                          VIR_DOMAIN_BLOCK_IOTUNE_WRITE_IOPS_SEC)) {
             info.write_iops_sec = param->value.ul;
+            set_iops = true;
         }
     }
 
@@ -11614,10 +11625,25 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
     }
 
     if (flags & VIR_DOMAIN_AFFECT_LIVE) {
+        /* If the user didn't specify bytes limits, inherit previous
+         * values; likewise if the user didn't specify iops
+         * limits.  */
+        oldinfo = &vm->def->disks[idx]->blkdeviotune;
+        if (!set_bytes) {
+            info.total_bytes_sec = oldinfo->total_bytes_sec;
+            info.read_bytes_sec = oldinfo->read_bytes_sec;
+            info.write_bytes_sec = oldinfo->write_bytes_sec;
+        }
+        if (!set_iops) {
+            info.total_iops_sec = oldinfo->total_iops_sec;
+            info.read_iops_sec = oldinfo->read_iops_sec;
+            info.write_iops_sec = oldinfo->write_iops_sec;
+        }
         priv = vm->privateData;
         qemuDomainObjEnterMonitorWithDriver(driver, vm);
         ret = qemuMonitorSetBlockIoThrottle(priv->mon, device, &info);
         qemuDomainObjExitMonitorWithDriver(driver, vm);
+        vm->def->disks[idx]->blkdeviotune = info;
         if (ret < 0)
             goto endjob;
     }
@@ -11627,6 +11653,17 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
         idx = virDomainDiskIndexByName(persistentDef, disk, true);
         if (idx < 0)
             goto endjob;
+        oldinfo = &persistentDef->disks[idx]->blkdeviotune;
+        if (!set_bytes) {
+            info.total_bytes_sec = oldinfo->total_bytes_sec;
+            info.read_bytes_sec = oldinfo->read_bytes_sec;
+            info.write_bytes_sec = oldinfo->write_bytes_sec;
+        }
+        if (!set_iops) {
+            info.total_iops_sec = oldinfo->total_iops_sec;
+            info.read_iops_sec = oldinfo->read_iops_sec;
+            info.write_iops_sec = oldinfo->write_iops_sec;
+        }
         persistentDef->disks[idx]->blkdeviotune = info;
         ret = virDomainSaveConfig(driver->configDir, persistentDef);
         if (ret < 0) {
@@ -11688,7 +11725,7 @@ qemuDomainGetBlockIoTune(virDomainPtr dom,
         goto cleanup;
     }
 
-    device = qemuDiskPathToAlias(vm, disk);
+    device = qemuDiskPathToAlias(vm, disk, NULL);
 
     if (!device) {
         goto cleanup;

tools/virsh.pod

@@ -604,8 +604,9 @@ I<--total_iops_sec> specifies total I/O operations limit per second.
 I<--read_iops_sec> specifies read I/O operations limit per second.
 I<--write_iops_sec> specifies write I/O operations limit per second.
 
-When setting any value, all remaining values are reset to unlimited,
-an explicit 0 also clears any limit.  A non-zero value for a given total
+Bytes and iops values are independent, but setting only one value (such
+as --read_bytes_sec) resets the other two in that category to unlimited.
+An explicit 0 also clears any limit.  A non-zero value for a given total
 cannot be mixed with non-zero values for read or write.
 
 If I<--live> is specified, affect a running guest.