Support detecting mountpoints correctly (#7288)

Currently windows support was relying on Symlink as
a way to detect a drive, this doesn't work in latest
Windows 2016, fix this to use a proper mechanism by
using win32 APIs.

Additionally also add support for detecting bind mounts
on Linux.

pkg/mountinfo/mountinfo_linux.go

@@ -37,24 +37,30 @@ const (
 )
 
 // IsLikelyMountPoint determines if a directory is a mountpoint.
-// It is fast but not necessarily ALWAYS correct. If the path is in fact
-// a bind mount from one part of a mount to another it will not be detected.
-// mkdir /tmp/a /tmp/b; mount --bin /tmp/a /tmp/b; IsLikelyMountPoint("/tmp/b")
-// will return false. When in fact /tmp/b is a mount point. If this situation
-// if of interest to you, don't use this function...
-func IsLikelyMountPoint(file string) bool {
-	stat, err := os.Stat(file)
+func IsLikelyMountPoint(path string) bool {
+	s1, err := os.Lstat(path)
 	if err != nil {
 		return false
 	}
 
-	rootStat, err := os.Lstat(filepath.Dir(strings.TrimSuffix(file, "/")))
+	// A symlink can never be a mount point
+	if s1.Mode()&os.ModeSymlink != 0 {
+		return false
+	}
+
+	s2, err := os.Lstat(filepath.Dir(strings.TrimSuffix(path, "/")))
 	if err != nil {
 		return false
 	}
 
 	// If the directory has a different device as parent, then it is a mountpoint.
-	return stat.Sys().(*syscall.Stat_t).Dev != rootStat.Sys().(*syscall.Stat_t).Dev
+	if s1.Sys().(*syscall.Stat_t).Dev != s2.Sys().(*syscall.Stat_t).Dev {
+		//  path/.. on a different device as path
+		return true
+	}
+
+	// path/.. is the same i-node as path - this check is for bind mounts.
+	return s1.Sys().(*syscall.Stat_t).Ino == s2.Sys().(*syscall.Stat_t).Ino
 }
 
 // CheckCrossDevice - check if any list of paths has any sub-mounts at /proc/mounts.