Check the validity of the platforms

platforms can still be added but some warning message
will be emitted if the platform cannot pass the validity
check.

Signed-off-by: Dave Chen <dave.chen@arm.com>

cmd/buildkitd/main.go

@@ -310,9 +310,13 @@ func setDefaultConfig(cfg *config.Config) {
 
 	if cfg.Workers.OCI.Platforms == nil {
 		cfg.Workers.OCI.Platforms = binfmt_misc.SupportedPlatforms()
+	} else {
+		binfmt_misc.ValidatePlatforms(cfg.Workers.OCI.Platforms)
 	}
 	if cfg.Workers.Containerd.Platforms == nil {
 		cfg.Workers.Containerd.Platforms = binfmt_misc.SupportedPlatforms()
+	} else {
+		binfmt_misc.ValidatePlatforms(cfg.Workers.Containerd.Platforms)
 	}
 
 	if system.RunningInUserNS() {

cmd/buildkitd/main_containerd_worker.go

@@ -10,6 +10,7 @@ import (
 
 	ctd "github.com/containerd/containerd"
 	"github.com/moby/buildkit/cmd/buildkitd/config"
+	"github.com/moby/buildkit/util/binfmt_misc"
 	"github.com/moby/buildkit/worker"
 	"github.com/moby/buildkit/worker/base"
 	"github.com/moby/buildkit/worker/containerd"
@@ -142,6 +143,7 @@ func applyContainerdFlags(c *cli.Context, cfg *config.Config) error {
 	}
 
 	if platforms := c.GlobalStringSlice("containerd-worker-platform"); len(platforms) != 0 {
+		binfmt_misc.ValidatePlatforms(platforms)
 		cfg.Workers.Containerd.Platforms = platforms
 	}
 

cmd/buildkitd/main_oci_worker.go

@@ -11,6 +11,7 @@ import (
 	"github.com/containerd/containerd/snapshots/overlay"
 	"github.com/moby/buildkit/cmd/buildkitd/config"
 	"github.com/moby/buildkit/executor/oci"
+	"github.com/moby/buildkit/util/binfmt_misc"
 	"github.com/moby/buildkit/worker"
 	"github.com/moby/buildkit/worker/base"
 	"github.com/moby/buildkit/worker/runc"
@@ -142,6 +143,7 @@ func applyOCIFlags(c *cli.Context, cfg *config.Config) error {
 	}
 
 	if platforms := c.GlobalStringSlice("oci-worker-platform"); len(platforms) != 0 {
+		binfmt_misc.ValidatePlatforms(platforms)
 		cfg.Workers.OCI.Platforms = platforms
 	}
 

util/binfmt_misc/amd64_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func amd64Supported() bool {
-	return check(Binaryamd64) == nil
+func amd64Supported() (string, error) {
+	return check(Binaryamd64)
 }

util/binfmt_misc/amd64_check_amd64.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func amd64Supported() bool {
-	return true
+func amd64Supported() (string, error) {
+	return "", nil
 }

util/binfmt_misc/arm64_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func arm64Supported() bool {
-	return check(Binaryarm64) == nil
+func arm64Supported() (string, error) {
+	return check(Binaryarm64)
 }

util/binfmt_misc/arm64_check_arm64.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func arm64Supported() bool {
-	return true
+func arm64Supported() (string, error) {
+	return "", nil
 }

util/binfmt_misc/arm_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func armSupported() bool {
-	return check(Binaryarm) == nil
+func armSupported() (string, error) {
+	return check(Binaryarm)
 }

util/binfmt_misc/arm_check_arm.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func armSupported() bool {
-	return true
+func armSupported() (string, error) {
+	return "", nil
 }

util/binfmt_misc/check.go

@@ -10,30 +10,36 @@ import (
 	"path/filepath"
 )
 
-func check(bin string) error {
+func check(bin string) (string, error) {
 	tmpdir, err := ioutil.TempDir("", "qemu-check")
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer os.RemoveAll(tmpdir)
 	pp := filepath.Join(tmpdir, "check")
 
 	r, err := gzip.NewReader(bytes.NewReader([]byte(bin)))
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer r.Close()
 
 	f, err := os.OpenFile(pp, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0700)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	if _, err := io.Copy(f, r); err != nil {
 		f.Close()
-		return err
+		return "", err
 	}
 	f.Close()
 
-	return exec.Command(pp).Run()
+	output, err := exec.Command(pp).CombinedOutput()
+	if err == nil {
+		cmd := exec.Command("chroot", ".", "/check")
+		cmd.Dir = tmpdir
+		output, err = cmd.CombinedOutput()
+	}
+	return string(output), err
 }

util/binfmt_misc/detect.go

@@ -5,6 +5,7 @@ import (
 	"sync"
 
 	"github.com/containerd/containerd/platforms"
+	"github.com/sirupsen/logrus"
 )
 
 var once sync.Once
@@ -14,19 +15,68 @@ func SupportedPlatforms() []string {
 	once.Do(func() {
 		def := platforms.DefaultString()
 		arr = append(arr, def)
-
-		if p := "linux/amd64"; def != p && amd64Supported() {
-			arr = append(arr, p)
+		if p := "linux/amd64"; def != p {
+			_, err := amd64Supported()
+			if err == nil {
+				arr = append(arr, p)
+			}
 		}
-		if p := "linux/arm64"; def != p && arm64Supported() {
-			arr = append(arr, p)
+		if p := "linux/arm64"; def != p {
+			_, err := arm64Supported()
+			if err == nil {
+				arr = append(arr, p)
+			}
 		}
-		if !strings.HasPrefix(def, "linux/arm/") && armSupported() {
-			arr = append(arr, "linux/arm/v7", "linux/arm/v6")
+		if !strings.HasPrefix(def, "linux/arm/") {
+			_, err := armSupported()
+			if err == nil {
+				arr = append(arr, "linux/arm/v7", "linux/arm/v6")
+			}
 		} else if def == "linux/arm/v7" {
 			arr = append(arr, "linux/arm/v6")
 		}
 	})
-
 	return arr
 }
+
+//Here, the func just validate the platforms and show warning message if there is,
+//the end user could fix the issue based on those warning, and thus no need to drop
+//the platfrom from the candidates.
+func ValidatePlatforms(pfs []string) {
+	def := platforms.DefaultString()
+	for _, p := range pfs {
+		if p != def {
+			if p == "linux/amd64" {
+				output, err := amd64Supported()
+				if err != nil {
+					printErr(p, output, err)
+				}
+			}
+			if p == "linux/arm64" {
+				output, err := arm64Supported()
+				if err != nil {
+					printErr(p, output, err)
+				}
+			}
+			if strings.HasPrefix(p, "linux/arm/v6") || strings.HasPrefix(p, "linux/arm/v7") {
+				output, err := armSupported()
+				if err != nil {
+					printErr(p, output, err)
+				}
+			}
+		}
+	}
+}
+
+//Only show the warning when the platforms are maually specified, show the message for the platforms
+//finding provided by `SupportedPlatforms` is a little annoying, no platform specifed but the warning
+//message is shown might confuse end users.
+func printErr(p string, output string, err error) {
+	if strings.Contains(err.Error(), "exec format error") {
+		logrus.Warnf("platform %s cannot pass the validation, kernel support for miscellaneous bianry may have not enabled.", p)
+	} else if strings.Contains(output, "No such file or director") {
+		logrus.Warnf("platforms %s cannot pass the validation, '-F' flag might have not set for 'binfmt_misc'.", p)
+	} else {
+		logrus.Warnf("platforms %s cannot pass the validation: %s", p, err.Error())
+	}
+}