block: Add cache-related options for block devices

Add block_device_cache_set, block_device_cache_direct and
block_device_cache_noflush.
They are cache-related options for block devices that are described in
https://github.com/qemu/qemu/blob/master/qapi/block-core.json.
block_device_cache_direct denotes whether use of O_DIRECT (bypass the host
page cache) is enabled.  block_device_cache_noflush denotes whether flush
requests for the device are ignored.
The json said they are supported since 2.9.
So add block_device_cache_set to control the cache options set to block
devices or not.  It will help to support the old version qemu.

Fixes: #956

Signed-off-by: Hui Zhu <teawater@hyper.sh>

pkg/katautils/config-settings.go

@@ -28,6 +28,9 @@ const defaultBridgesCount uint32 = 1
 const defaultInterNetworkingModel = "macvtap"
 const defaultDisableBlockDeviceUse bool = false
 const defaultBlockDeviceDriver = "virtio-scsi"
+const defaultBlockDeviceCacheSet bool = false
+const defaultBlockDeviceCacheDirect bool = false
+const defaultBlockDeviceCacheNoflush bool = false
 const defaultEnableIOThreads bool = false
 const defaultEnableMemPrealloc bool = false
 const defaultEnableHugePages bool = false

pkg/katautils/config.go

@@ -89,6 +89,9 @@ type hypervisor struct {
 	MachineType             string `toml:"machine_type"`
 	BlockDeviceDriver       string `toml:"block_device_driver"`
 	EntropySource           string `toml:"entropy_source"`
+	BlockDeviceCacheSet     bool   `toml:"block_device_cache_set"`
+	BlockDeviceCacheDirect  bool   `toml:"block_device_cache_direct"`
+	BlockDeviceCacheNoflush bool   `toml:"block_device_cache_noflush"`
 	NumVCPUs                int32  `toml:"default_vcpus"`
 	DefaultMaxVCPUs         uint32 `toml:"default_maxvcpus"`
 	MemorySize              uint32 `toml:"default_memory"`
@@ -437,6 +440,9 @@ func newQemuHypervisorConfig(h hypervisor) (vc.HypervisorConfig, error) {
 		Debug:                   h.Debug,
 		DisableNestingChecks:    h.DisableNestingChecks,
 		BlockDeviceDriver:       blockDriver,
+		BlockDeviceCacheSet:     h.BlockDeviceCacheSet,
+		BlockDeviceCacheDirect:  h.BlockDeviceCacheDirect,
+		BlockDeviceCacheNoflush: h.BlockDeviceCacheNoflush,
 		EnableIOThreads:         h.EnableIOThreads,
 		Msize9p:                 h.msize9p(),
 		UseVSock:                useVSock,
@@ -555,6 +561,9 @@ func initConfig() (config oci.RuntimeConfig, err error) {
 		Debug:                   defaultEnableDebug,
 		DisableNestingChecks:    defaultDisableNestingChecks,
 		BlockDeviceDriver:       defaultBlockDeviceDriver,
+		BlockDeviceCacheSet:     defaultBlockDeviceCacheSet,
+		BlockDeviceCacheDirect:  defaultBlockDeviceCacheDirect,
+		BlockDeviceCacheNoflush: defaultBlockDeviceCacheNoflush,
 		EnableIOThreads:         defaultEnableIOThreads,
 		Msize9p:                 defaultMsize9p,
 		HotplugVFIOOnRootBus:    defaultHotplugVFIOOnRootBus,

virtcontainers/hypervisor.go

@@ -206,6 +206,17 @@ type HypervisorConfig struct {
 	// it will be used for the sandbox's kernel path instead of KernelPath.
 	customAssets map[assetType]*asset
 
+	// BlockDeviceCacheSet specifies cache-related options will be set to block devices or not.
+	BlockDeviceCacheSet bool
+
+	// BlockDeviceCacheDirect specifies cache-related options for block devices.
+	// Denotes whether use of O_DIRECT (bypass the host page cache) is enabled.
+	BlockDeviceCacheDirect bool
+
+	// BlockDeviceCacheNoflush specifies cache-related options for block devices.
+	// Denotes whether flush requests for the device are ignored.
+	BlockDeviceCacheNoflush bool
+
 	// DisableBlockDeviceUse disallows a block device from being used.
 	DisableBlockDeviceUse bool
 

virtcontainers/qemu.go

@@ -736,7 +736,12 @@ func (q *qemu) hotplugBlockDevice(drive *config.BlockDrive, op operation) error
 	devID := "virtio-" + drive.ID
 
 	if op == addDevice {
-		if err := q.qmpMonitorCh.qmp.ExecuteBlockdevAdd(q.qmpMonitorCh.ctx, drive.File, drive.ID); err != nil {
+		if q.config.BlockDeviceCacheSet {
+			err = q.qmpMonitorCh.qmp.ExecuteBlockdevAddWithCache(q.qmpMonitorCh.ctx, drive.File, drive.ID, q.config.BlockDeviceCacheDirect, q.config.BlockDeviceCacheNoflush)
+		} else {
+			err = q.qmpMonitorCh.qmp.ExecuteBlockdevAdd(q.qmpMonitorCh.ctx, drive.File, drive.ID)
+		}
+		if err != nil {
 			return err
 		}