This patch adds --tmpfs as a option for mounting tmpfs on directories

It will Tar up contents of child directory onto tmpfs if mounted over

This patch will use the new PreMount and PostMount hooks to "tar"
up the contents of the base image on top of tmpfs mount points.

Signed-off-by: Dan Walsh <dwalsh@redhat.com>

mount/flags.go

@@ -1,6 +1,7 @@
 package mount
 
 import (
+	"fmt"
 	"strings"
 )
 
@@ -67,3 +68,24 @@ func parseOptions(options string) (int, string) {
 	}
 	return flag, strings.Join(data, ",")
 }
+
+// ParseTmpfsOptions parse fstab type mount options into flags and data
+func ParseTmpfsOptions(options string) (int, string, error) {
+	flags, data := parseOptions(options)
+	validFlags := map[string]bool{
+		"size":      true,
+		"mode":      true,
+		"uid":       true,
+		"gid":       true,
+		"nr_inodes": true,
+		"nr_blocks": true,
+		"mpol":      true,
+	}
+	for _, o := range strings.Split(data, ",") {
+		opt := strings.SplitN(o, "=", 2)
+		if !validFlags[opt[0]] {
+			return 0, "", fmt.Errorf("Invalid tmpfs option %q", opt)
+		}
+	}
+	return flags, data, nil
+}