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+RBD Incremental Backup
+======================
+
+This is a simple streaming file format for representing a diff between
+two snapshots (or a snapshot and the head) of an RBD image.
+
+Header
+~~~~~~
+
+"rbd diff v1\\n"
+
+Metadata records
+~~~~~~~~~~~~~~~~
+
+Every record has a one byte "tag" that identifies the record type,
+followed by some other data.
+
+Metadata records come in the first part of the image.  Order is not
+important, as long as all the metadata records come before the data
+records.
+
+From snap
+---------
+
+- u8: 'f'
+- le32: snap name length
+- snap name
+
+To snap
+-------
+
+- u8: 't'
+- le32: snap name length
+- snap name
+
+Size
+----
+
+- u8: 's'
+- le64: (ending) image size
+
+Data Records
+~~~~~~~~~~~~
+
+These records come in the second part of the sequence.
+
+Updated data
+------------
+
+- u8: 'w'
+- le64: offset
+- le64: length
+- length bytes of actual data
+
+Zero data
+---------
+
+- u8: 'z'
+- le64: offset
+- le64: length
+
+
+Final Record
+~~~~~~~~~~~~
+
+End
+---
+
+- u8: 'e'
+
+
+Header
+~~~~~~
+
+"rbd diff v2\\n"
+
+Metadata records
+~~~~~~~~~~~~~~~~
+
+Every record has a one byte "tag" that identifies the record type,
+followed by length of data, and then some other data.
+
+Metadata records come in the first part of the image.  Order is not
+important, as long as all the metadata records come before the data
+records.
+
+In v2, we have the following metadata in each section:
+(1 Bytes) tag.
+(8 Bytes) length.
+(n Bytes) data.
+
+In this way, we can skip the unrecognized tag.
+
+From snap
+---------
+
+- u8: 'f'
+- le64: length of appending data (4 + length)
+- le32: snap name length
+- snap name
+
+To snap
+-------
+
+- u8: 't'
+- le64: length of appending data (4 + length)
+- le32: snap name length
+- snap name
+
+Size
+----
+
+- u8: 's'
+- le64: length of appending data (8)
+- le64: (ending) image size
+
+Data Records
+~~~~~~~~~~~~
+
+These records come in the second part of the sequence.
+
+Updated data
+------------
+
+- u8: 'w'
+- le64: length of appending data (8 + 8 + length)
+- le64: offset
+- le64: length
+- length bytes of actual data
+
+Zero data
+---------
+
+- u8: 'z'
+- le64: length of appending data (8 + 8)
+- le64: offset
+- le64: length
+
+
+Final Record
+~~~~~~~~~~~~
+
+End
+---
+
+- u8: 'e'