Implement overlay fs snapshot driver

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

mount.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"syscall"
 )
 
 // Mount is the lingua franca of the containerkit. A mount represents a
@@ -48,3 +49,67 @@ func MountAll(mounts ...Mount) error {
 
 	return nil
 }
+
+func MountFS(mounts []Mount, target string) error {
+	for _, m := range mounts {
+		flags, data := parseMountOptions(m.Options)
+		if err := syscall.Mount(m.Source, target, m.Type, uintptr(flags), data); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// parseMountOptions takes fstab style mount options and parses them for
+// use with a standard mount() syscall
+func parseMountOptions(options []string) (int, string) {
+	var (
+		flag int
+		data []string
+	)
+	flags := map[string]struct {
+		clear bool
+		flag  int
+	}{
+		"async":         {true, syscall.MS_SYNCHRONOUS},
+		"atime":         {true, syscall.MS_NOATIME},
+		"bind":          {false, syscall.MS_BIND},
+		"defaults":      {false, 0},
+		"dev":           {true, syscall.MS_NODEV},
+		"diratime":      {true, syscall.MS_NODIRATIME},
+		"dirsync":       {false, syscall.MS_DIRSYNC},
+		"exec":          {true, syscall.MS_NOEXEC},
+		"mand":          {false, syscall.MS_MANDLOCK},
+		"noatime":       {false, syscall.MS_NOATIME},
+		"nodev":         {false, syscall.MS_NODEV},
+		"nodiratime":    {false, syscall.MS_NODIRATIME},
+		"noexec":        {false, syscall.MS_NOEXEC},
+		"nomand":        {true, syscall.MS_MANDLOCK},
+		"norelatime":    {true, syscall.MS_RELATIME},
+		"nostrictatime": {true, syscall.MS_STRICTATIME},
+		"nosuid":        {false, syscall.MS_NOSUID},
+		"rbind":         {false, syscall.MS_BIND | syscall.MS_REC},
+		"relatime":      {false, syscall.MS_RELATIME},
+		"remount":       {false, syscall.MS_REMOUNT},
+		"ro":            {false, syscall.MS_RDONLY},
+		"rw":            {true, syscall.MS_RDONLY},
+		"strictatime":   {false, syscall.MS_STRICTATIME},
+		"suid":          {true, syscall.MS_NOSUID},
+		"sync":          {false, syscall.MS_SYNCHRONOUS},
+	}
+	for _, o := range options {
+		// If the option does not exist in the flags table or the flag
+		// is not supported on the platform,
+		// then it is a data value for a specific fs type
+		if f, exists := flags[o]; exists && f.flag != 0 {
+			if f.clear {
+				flag &= ^f.flag
+			} else {
+				flag |= f.flag
+			}
+		} else {
+			data = append(data, o)
+		}
+	}
+	return flag, strings.Join(data, ",")
+}