add d_type warning to docker info, and optimize output

The overlay(2) drivers were moved up in the list of storage drivers,
and are known to have problems if the backing filesystem does not
support d_type.

Commit 2e20e63da2a8a0ffbbb3f2146f87559e17f43046 added a warning,
which is logged in the daemon logs, however, many users do not
check those logs, and may overlook this warning.

This patch adds the same warning to the output of `docker info`
so that the warning is more easily found.

In addition, the output of warnings printed by `docker info` is
optimized, by;

- moving all warnings to the _end_ of the output, instead of
  mixing them with the regular output
- wrapping the storage-driver warnings, so that they are more
  easily readable

Example output with this patch applied
============================================

devicemapper using loopback devices:

    ...
    Insecure Registries:
     127.0.0.0/8
    Live Restore Enabled: false

    WARNING: devicemapper: usage of loopback devices is strongly discouraged for production use.
             Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.
    WARNING: bridge-nf-call-iptables is disabled
    WARNING: bridge-nf-call-ip6tables is disabled

overlay2 on xfs without d_type support;

    ...
    Insecure Registries:
     127.0.0.0/8
    Live Restore Enabled: false

    WARNING: overlay2: the backing xfs filesystem is formatted without d_type support, which leads to incorrect behavior.
             Reformat the filesystem with ftype=1 to enable d_type support.
             Running without d_type support will not be supported in future releases.
    WARNING: bridge-nf-call-iptables is disabled

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

command/system/info.go

@@ -6,8 +6,6 @@ import (
 	"strings"
 	"time"
 
-	"golang.org/x/net/context"
-
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/swarm"
 	"github.com/docker/docker/cli"
@@ -17,6 +15,7 @@ import (
 	"github.com/docker/docker/pkg/templates"
 	"github.com/docker/go-units"
 	"github.com/spf13/cobra"
+	"golang.org/x/net/context"
 )
 
 type infoOptions struct {
@@ -66,11 +65,6 @@ func prettyPrintInfo(dockerCli *command.DockerCli, info types.Info) error {
 	if info.DriverStatus != nil {
 		for _, pair := range info.DriverStatus {
 			fmt.Fprintf(dockerCli.Out(), " %s: %s\n", pair[0], pair[1])
-
-			// print a warning if devicemapper is using a loopback file
-			if pair[0] == "Data loop file" {
-				fmt.Fprintln(dockerCli.Err(), " WARNING: Usage of loopback devices is strongly discouraged for production use. Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.")
-			}
 		}
 
 	}
@@ -228,43 +222,6 @@ func prettyPrintInfo(dockerCli *command.DockerCli, info types.Info) error {
 		fmt.Fprintf(dockerCli.Out(), "Registry: %v\n", info.IndexServerAddress)
 	}
 
-	// Only output these warnings if the server does not support these features
-	if info.OSType != "windows" {
-		if !info.MemoryLimit {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No memory limit support")
-		}
-		if !info.SwapLimit {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No swap limit support")
-		}
-		if !info.KernelMemory {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No kernel memory limit support")
-		}
-		if !info.OomKillDisable {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No oom kill disable support")
-		}
-		if !info.CPUCfsQuota {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu cfs quota support")
-		}
-		if !info.CPUCfsPeriod {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu cfs period support")
-		}
-		if !info.CPUShares {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu shares support")
-		}
-		if !info.CPUSet {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpuset support")
-		}
-		if !info.IPv4Forwarding {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: IPv4 forwarding is disabled")
-		}
-		if !info.BridgeNfIptables {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: bridge-nf-call-iptables is disabled")
-		}
-		if !info.BridgeNfIP6tables {
-			fmt.Fprintln(dockerCli.Err(), "WARNING: bridge-nf-call-ip6tables is disabled")
-		}
-	}
-
 	if info.Labels != nil {
 		fmt.Fprintln(dockerCli.Out(), "Labels:")
 		for _, attribute := range info.Labels {
@@ -317,11 +274,85 @@ func prettyPrintInfo(dockerCli *command.DockerCli, info types.Info) error {
 		}
 	}
 
-	fmt.Fprintf(dockerCli.Out(), "Live Restore Enabled: %v\n", info.LiveRestoreEnabled)
+	fmt.Fprintf(dockerCli.Out(), "Live Restore Enabled: %v\n\n", info.LiveRestoreEnabled)
+
+	// Only output these warnings if the server does not support these features
+	if info.OSType != "windows" {
+		printStorageDriverWarnings(dockerCli, info)
+
+		if !info.MemoryLimit {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No memory limit support")
+		}
+		if !info.SwapLimit {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No swap limit support")
+		}
+		if !info.KernelMemory {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No kernel memory limit support")
+		}
+		if !info.OomKillDisable {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No oom kill disable support")
+		}
+		if !info.CPUCfsQuota {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu cfs quota support")
+		}
+		if !info.CPUCfsPeriod {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu cfs period support")
+		}
+		if !info.CPUShares {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpu shares support")
+		}
+		if !info.CPUSet {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: No cpuset support")
+		}
+		if !info.IPv4Forwarding {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: IPv4 forwarding is disabled")
+		}
+		if !info.BridgeNfIptables {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: bridge-nf-call-iptables is disabled")
+		}
+		if !info.BridgeNfIP6tables {
+			fmt.Fprintln(dockerCli.Err(), "WARNING: bridge-nf-call-ip6tables is disabled")
+		}
+	}
 
 	return nil
 }
 
+func printStorageDriverWarnings(dockerCli *command.DockerCli, info types.Info) {
+	if info.DriverStatus == nil {
+		return
+	}
+
+	for _, pair := range info.DriverStatus {
+		if pair[0] == "Data loop file" {
+			fmt.Fprintf(dockerCli.Err(), "WARNING: %s: usage of loopback devices is strongly discouraged for production use.\n         Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.\n", info.Driver)
+		}
+		if pair[0] == "Supports d_type" && pair[1] == "false" {
+			backingFs := getBackingFs(info)
+
+			msg := fmt.Sprintf("WARNING: %s: the backing %s filesystem is formatted without d_type support, which leads to incorrect behavior.\n", info.Driver, backingFs)
+			if backingFs == "xfs" {
+				msg += "         Reformat the filesystem with ftype=1 to enable d_type support.\n"
+			}
+			msg += "         Running without d_type support will not be supported in future releases."
+			fmt.Fprintln(dockerCli.Err(), msg)
+		}
+	}
+}
+
+func getBackingFs(info types.Info) string {
+	if info.DriverStatus == nil {
+		return ""
+	}
+
+	for _, pair := range info.DriverStatus {
+		if pair[0] == "Backing Filesystem" {
+			return pair[1]
+		}
+	}
+	return ""
+}
+
 func formatInfo(dockerCli *command.DockerCli, info types.Info, format string) error {
 	tmpl, err := templates.Parse(format)
 	if err != nil {