Documentation/device-mapper/dm-bow.txt

23 that sector 0 is used to keep a log of the latest changes, both to indicate that
27 State 2: The transition to state 2 triggers replacing the special sector 0 with
28 the normal sector 0, and the freeing of all state information. dm_bow then
48 dm_bow maintains a type for all sectors. A sector can be any of:
57 SECTOR0 is the first sector on the device, and is used to hold the log of
60 SECTOR0_CURRENT is a sector picked from the FREE sectors, and is where reads and
61 writes from the true sector zero are redirected to. Note that like any backup
62 sector, if the sector is written to directly, it must be moved again.
64 UNCHANGED means that the sector has not been changed since we entered state 1.
67 FREE means that the sector was trimmed in state 0 and has not yet been written
68 to or used for backup. On being written to, a FREE sector is changed to CHANGED.
70 CHANGED means that the sector has been modified, and can be further modified
73 BACKUP means that this is a free sector being used as a backup. On being written
76 All backup operations are logged to the first sector. The log sector has the
89 When SECTOR0 is full, the log sector is backed up and another empty log sector
92 sector. Note that sequence is not strictly needed, but is a useful sanity check
97 sector 0 are copied there. The sector 0 is backed up, which triggers the first