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Redundancy file operation library (librefop)
Redundancy file operation library is a another implementation for the backup
manager of AGL base system. It aim to tiny implementation.
File operation algorithm
New data write - case 1..
1-0. Initial state.
--------
| latest |
| file |
--------
1-1. Create new file.
--------
| New |
| file |
--------
--------
| latest |
| file |
--------
1-2. Rename from latest file to backup file.
--------
| New |
| file |
--------
--------
--> | backup |
rename | file |
--------
1-3. Create new data file.
| rename from new to latest
-------- --------
| latest | | backup |
| file | | file |
-------- --------
1-4. Done.
New data write - case 2.
2-0. Initial state.
-------- --------
| latest | | backup |
| file | | file |
-------- --------
2-1. Create new file.
--------
| New |
| file |
--------
-------- --------
| latest | | backup |
| file | | file |
-------- --------
2-2. Remove backup file.
--------
| New |
| file |
--------
--------
| latest | remove
| file | backup file
--------
2-3. Rename from latest file to backup file.
--------
| New |
| file |
--------
--------
--> | backup |
rename | file |
--------
2-4. Create new data file.
| rename from new to latest
-------- --------
| latest | | backup |
| file | | file |
-------- --------
2-5. Remove oldest backup file.
-------- --------
| New | | backup |
| file | | file |
-------- --------
2-6. Done.
Recovery from abnormal conditions.
Note. 'p1,p2' is a file selection priority. [High pri.] p1 > p2 [Low pri.]
ac1. Nodata
Return a no data.
ac2. Latest file only.
--------
| latest |
| file |
--------
p1
Return data from a latest file.
ac3. Backup file only.
--------
| backup |
| file |
--------
p1
Return data from a backup file.
ac4. Have a two file (normal condition).
-------- --------
| latest | | backup |
| file | | file |
-------- --------
p1 p2
Return data from a latest file.
ac5. Latest file and new file.
--------
| New |
| file |
--------
--------
| latest |
| file |
--------
p1
Return data from a new file. Typically new file may not completed write operation.
ac6. Backup file and new file.
--------
| New |
| file |
--------
--------
| backup |
| file |
--------
p1
Return data from a backup file. Typically new file may not completed write operation.
ac7. Latest file and backup file and new file.
--------
| New |
| file |
--------
-------- --------
| latest | | backup |
| file | | file |
-------- --------
p1 p2
Return data from a latest file. Typically new file may not completed write operation.
When the data block of high priority file was broken, this library select next priority file.
|
