Add support for bind-mounts on Darwin

Signed-off-by: Marat Radchenko <[email protected]>

core/mount/mount.go

@@ -27,7 +27,7 @@ import (
 )
 
 // HasBindMounts This is a flag to conditionally disable code that relies on working bind-mount support, so such code is easier to find across codebase.
-const HasBindMounts = runtime.GOOS != "darwin" && runtime.GOOS != "openbsd"
+const HasBindMounts = runtime.GOOS != "openbsd"
 
 // Mount is the lingua franca of containerd. A mount represents a
 // serialized mount syscall. Components either emit or consume mounts.

core/mount/mount_darwin.go

@@ -16,9 +16,39 @@
 
 package mount
 
-import "github.com/containerd/errdefs"
+import (
+	"fmt"
+	"os/exec"
+)
 
 // Mount to the provided target.
 func (m *Mount) mount(target string) error {
-	return errdefs.ErrNotImplemented
+	var commandName string
+	if m.Type == "bind" {
+		// macOS doesn't natively support bindfs/nullfs
+		// The way to emulate it is via FUSE fs named "bindfs"
+		commandName = "bindfs"
+	} else {
+		commandName = fmt.Sprintf("mount_%s", m.Type)
+	}
+
+	var args []string
+	for _, option := range m.Options {
+		if option == "rbind" {
+			// On one side, rbind is not supported by macOS mounting tools
+			// On the other, bindfs works as if rbind is enabled anyway
+			continue
+		}
+
+		args = append(args, "-o", option)
+	}
+	args = append(args, m.Source, target)
+
+	cmd := exec.Command(commandName, args...)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("%s [%v] failed: %q: %w", commandName, args, string(output), err)
+	}
+
+	return nil
 }