libct/cg/sd/v2: warn about old systemd

1. Add a check to unifiedResToSystemdProps that systemd is recent enough
   to support AllowedCPUs/AllowedMemoryNodes unit properties, and skip
   setting the property if it is not supported.

   Note that this is not an error as the setting is still applied to
   the underlying cgroupfs -- it's just systemd unit property that is
   being skipped.

2. In all the places we skip an unsupported property, warn about it.

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

libcontainer/cgroups/systemd/common.go

@@ -409,6 +409,9 @@ func addCpuQuota(conn *systemdDbus.Conn, properties *[]systemdDbus.Property, quo
 		if sdVer >= 242 {
 			*properties = append(*properties,
 				newProp("CPUQuotaPeriodUSec", period))
+		} else {
+			logrus.Warnf("systemd v%d is too old to support CPUQuotaPeriodSec "+
+				" (setting will still be applied to cgroupfs)", sdVer)
 		}
 	}
 	if quota != 0 || period != 0 {
@@ -441,6 +444,8 @@ func addCpuset(conn *systemdDbus.Conn, props *[]systemdDbus.Property, cpus, mems
 	// systemd only supports AllowedCPUs/AllowedMemoryNodes since v244
 	sdVer := systemdVersion(conn)
 	if sdVer < 244 {
+		logrus.Warnf("systemd v%d is too old to support AllowedCPUs/AllowedMemoryNodes"+
+			" (settings will still be applied to cgroupfs)", sdVer)
 		return nil
 	}
 

libcontainer/cgroups/systemd/v2.go

@@ -102,8 +102,16 @@ func unifiedResToSystemdProps(conn *systemdDbus.Conn, res map[string]string) (pr
 				"cpuset.cpus": "AllowedCPUs",
 				"cpuset.mems": "AllowedMemoryNodes",
 			}
-			props = append(props,
-				newProp(m[k], bits))
+			// systemd only supports these properties since v244
+			sdVer := systemdVersion(conn)
+			if sdVer >= 244 {
+				props = append(props,
+					newProp(m[k], bits))
+			} else {
+				logrus.Warnf("systemd v%d is too old to support %s"+
+					" (setting will still be applied to cgroupfs)",
+					sdVer, m[k])
+			}
 
 		case "memory.high", "memory.low", "memory.min", "memory.max", "memory.swap.max":
 			num := uint64(math.MaxUint64)