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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'