Make mount type and source optional

These are optional on multiple platforms and should be left up to the
runtime/host system for validation.

Closes opencontainers#470

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

config.md

@@ -57,11 +57,11 @@ For Windows, see links for details about [mountvol](http://ss64.com/nt/mountvol.
   This value MUST be an absolute path.
   * Windows: one mount destination MUST NOT be nested within another mount (e.g., c:\\foo and c:\\foo\\bar).
   * Solaris: corresponds to "dir" of the fs resource in zonecfg(8).
-* **`type`** (string, REQUIRED) The filesystem type of the filesystem to be mounted.
+* **`type`** (string, OPTIONAL) The filesystem type of the filesystem to be mounted.
   * Linux: valid *filesystemtype* supported by the kernel as listed in */proc/filesystems* (e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs", "msdos", "proc", "nfs", "iso9660").
   * Windows: the type of file system on the volume, e.g. "ntfs".
   * Solaris: corresponds to "type" of the fs resource in zonecfg(8).
-* **`source`** (string, REQUIRED) A device name, but can also be a directory name or a dummy.
+* **`source`** (string, OPTIONAL) A device name, but can also be a directory name or a dummy.
   * Windows: the volume name that is the target of the mount point, \\?\Volume\{GUID}\ (on Windows source is called target).
   * Solaris: corresponds to "special" of the fs resource in zonecfg(8).
 * **`options`** (list of strings, OPTIONAL) Mount options of the filesystem to be used.

schema/defs.json

@@ -140,9 +140,7 @@
                 }
             },
             "required": [
-                "destination",
-                "source",
-                "type"
+                "destination"
             ]
         },
         "ociVersion": {

specs-go/config.go

@@ -113,10 +113,10 @@ type Mount struct {
 	// Destination is the path where the mount will be placed relative to the container's root.  The path and child directories MUST exist, a runtime MUST NOT create directories automatically to a mount point.
 	Destination string `json:"destination"`
 	// Type specifies the mount kind.
-	Type string `json:"type"`
+	Type string `json:"type,omitempty"`
 	// Source specifies the source path of the mount.  In the case of bind mounts on
 	// Linux based systems this would be the file on the host.
-	Source string `json:"source"`
+	Source string `json:"source,omitempty"`
 	// Options are fstab style mount options.
 	Options []string `json:"options,omitempty"`
 }