- /* imsm does not track uuid's so just make sure we never return
- * the same value twice to break uuid matching in Manage_subdevs
- * FIXME what about the use of uuid's with bitmap's?
+ /* The uuid returned here is used for:
+ * uuid to put into bitmap file (Create, Grow)
+ * uuid for backup header when saving critical section (Grow)
+ * comparing uuids when re-adding a device into an array
+ * In these cases the uuid required is that of the data-array,
+ * not the device-set.
+ * uuid to recognise same set when adding a missing device back
+ * to an array. This is a uuid for the device-set.
+ *
+ * For each of these we can make do with a truncated
+ * or hashed uuid rather than the original, as long as
+ * everyone agrees.
+ * In each case the uuid required is that of the data-array,
+ * not the device-set.
+ */
+ /* imsm does not track uuid's so we synthesis one using sha1 on
+ * - The signature (Which is constant for all imsm array, but no matter)
+ * - the family_num of the container
+ * - the index number of the volume
+ * - the 'serial' number of the volume.
+ * Hopefully these are all constant.