libct/cg/fs2: set io weight if possible

Per-device weight is supported since kernel v5.4 (kernel commit
795fe54c2a8), so let's set those if supplied.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs2/io.go

@@ -17,6 +17,7 @@ import (
 
 func isIoSet(r *configs.Resources) bool {
 	return r.BlkioWeight != 0 ||
+		len(r.BlkioWeightDevice) > 0 ||
 		len(r.BlkioThrottleReadBpsDevice) > 0 ||
 		len(r.BlkioThrottleWriteBpsDevice) > 0 ||
 		len(r.BlkioThrottleReadIOPSDevice) > 0 ||
@@ -28,9 +29,10 @@ func setIo(dirPath string, r *configs.Resources) error {
 		return nil
 	}
 
+	const bfqWeight = "io.bfq.weight"
+
 	if r.BlkioWeight != 0 {
-		filename := "io.bfq.weight"
-		if err := fscommon.WriteFile(dirPath, filename,
+		if err := fscommon.WriteFile(dirPath, bfqWeight,
 			strconv.FormatUint(uint64(r.BlkioWeight), 10)); err != nil {
 			// if io.bfq.weight does not exist, then bfq module is not loaded.
 			// Fallback to use io.weight with a conversion scheme
@@ -43,6 +45,16 @@ func setIo(dirPath string, r *configs.Resources) error {
 			}
 		}
 	}
+	for _, wd := range r.BlkioWeightDevice {
+		// per-device weight is supported since kernel v5.4, commit 795fe54c2a8.
+		if err := fscommon.WriteFile(dirPath, bfqWeight, wd.WeightString()); err != nil {
+			if os.IsNotExist(err) {
+				// Kernel module bfq is not loaded -- ignore it.
+				break
+			}
+			return err
+		}
+	}
 	for _, td := range r.BlkioThrottleReadBpsDevice {
 		if err := fscommon.WriteFile(dirPath, "io.max", td.StringName("rbps")); err != nil {
 			return err