portallocator: log instead of discard port-range failures

Both getDynamicPortRange() and sanitizePortRange() could produce
and error, and the error message was currently discarded, silently
falling back to using the default port range.

This patch:

- Moves the fallback message from getDynamicPortRange() to getDefaultPortRange(),
  which is where the actual fallback occurs.
- Logs the fallback message and the error that causes the fallback.

The message/error is currently printed at the INFO level, but could be raised
to a WARN, depending on what kind of situations can cause the error.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/portallocator/portallocator.go

@@ -110,6 +110,7 @@ func getDefaultPortRange() (int, int) {
 		start, end, err = sanitizePortRange(start, end)
 	}
 	if err != nil {
+		logrus.WithError(err).Infof("falling back to default port range %d-%d", defaultPortRangeStart, defaultPortRangeEnd)
 		start, end = defaultPortRangeStart, defaultPortRangeEnd
 	}
 	return start, end

libnetwork/portallocator/portallocator_freebsd.go

@@ -8,20 +8,19 @@ import (
 
 func getDynamicPortRange() (start int, end int, err error) {
 	portRangeKernelSysctl := []string{"net.inet.ip.portrange.hifirst", "net.ip.portrange.hilast"}
-	portRangeFallback := fmt.Sprintf("using fallback port range %d-%d", defaultPortRangeStart, defaultPortRangeEnd)
 	portRangeLowCmd := exec.Command("/sbin/sysctl", portRangeKernelSysctl[0])
 	var portRangeLowOut bytes.Buffer
 	portRangeLowCmd.Stdout = &portRangeLowOut
 	cmdErr := portRangeLowCmd.Run()
 	if cmdErr != nil {
-		return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hifirst failed - %s: %v", portRangeFallback, err)
+		return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hifirst failed: %v", err)
 	}
 	n, err := fmt.Sscanf(portRangeLowOut.String(), "%d", &start)
 	if n != 1 || err != nil {
 		if err == nil {
 			err = fmt.Errorf("unexpected count of parsed numbers (%d)", n)
 		}
-		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range start from %s - %s: %v", portRangeLowOut.String(), portRangeFallback, err)
+		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range start from %s: %v", portRangeLowOut.String(), err)
 	}
 
 	portRangeHighCmd := exec.Command("/sbin/sysctl", portRangeKernelSysctl[1])
@@ -29,14 +28,14 @@ func getDynamicPortRange() (start int, end int, err error) {
 	portRangeHighCmd.Stdout = &portRangeHighOut
 	cmdErr = portRangeHighCmd.Run()
 	if cmdErr != nil {
-		return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hilast failed - %s: %v", portRangeFallback, err)
+		return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hilast failed: %v", err)
 	}
 	n, err = fmt.Sscanf(portRangeHighOut.String(), "%d", &end)
 	if n != 1 || err != nil {
 		if err == nil {
 			err = fmt.Errorf("unexpected count of parsed numbers (%d)", n)
 		}
-		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range end from %s - %s: %v", portRangeHighOut.String(), portRangeFallback, err)
+		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range end from %s: %v", portRangeHighOut.String(), err)
 	}
 	return start, end, nil
 }

libnetwork/portallocator/portallocator_linux.go

@@ -8,12 +8,10 @@ import (
 
 func getDynamicPortRange() (start int, end int, err error) {
 	const portRangeKernelParam = "/proc/sys/net/ipv4/ip_local_port_range"
-	portRangeFallback := fmt.Sprintf("using fallback port range %d-%d", defaultPortRangeStart, defaultPortRangeEnd)
 	file, err := os.Open(portRangeKernelParam)
 	if err != nil {
-		return 0, 0, fmt.Errorf("port allocator - %s due to error: %v", portRangeFallback, err)
+		return 0, 0, err
 	}
-
 	defer file.Close()
 
 	n, err := fmt.Fscanf(bufio.NewReader(file), "%d\t%d", &start, &end)
@@ -21,7 +19,7 @@ func getDynamicPortRange() (start int, end int, err error) {
 		if err == nil {
 			err = fmt.Errorf("unexpected count of parsed numbers (%d)", n)
 		}
-		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range from %s - %s: %v", portRangeKernelParam, portRangeFallback, err)
+		return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range from %s: %v", portRangeKernelParam, err)
 	}
 	return start, end, nil
 }