pubfork / f2f

#f2f Library 0.8#

C++ library primarily aimed as file-system-in-file implementation. But it also may be used to provide file system service on different kinds of storage (see f2f::IStorage interface).

##Features##

• Up to petabytes storage size
• No limitation on file size or number
• No limitation on directory size
• Easy to use C++ API

##Requirements##

Library is written on portable C++11 and uses Boost library (>= 1.55). f2f was tested with these compilers:

• Visual Studio 2015
• GCC 4.9 (-std=c++14)

##Storage format##

Small header precedes storage data:

Storage Header	Block storage
struct StorageHeader	...

Block storage is a organized as a tree of occupancy groups. Each occupancy group contains information about free and occupied subgroups. This information is stored as a bitmap - block, in which each bit is 1 if corresponding subgroup is fully occupied and 0 if it has free blocks.

Level i-1 Group 0	Level i Bitmap block	Level i-1 Group 1	...	Level i-1 Group 8095
...	1Kb	...	...

Occupancy groups of level 0 has different format:

Level 0 Bitmap block	Data block 0	Data block 1	...	Data block 8095
1Kb	1Kb	1Kb	...	1Kb

Data blocks are referenced by continuous index numbers throughout library. Bitmap blocks aren't referenced outside the f2f::BlockStorage class.

Only minimal required number of blocks is reserved in storage. Occupancy groups may be truncated after whole data block.

##Files##

Each file is identified by index of its inode block. inode block (see f2f::format::FileInode) contains references to ranges of file data blocks and some metadata. These references may be organized as B+tree scattered on several blocks (see f2f::format::BlockRangesInternalNode and f2f::format::BlockRangesLeafNode for format of tree nodes).

##Directories##

Directory contains references to files and other directories together with their names. Each directory is identified by index of its inode block. inode block (see f2f::format::DirectoryInode) contains records of directory entries (f2f::format::DirectoryTreeLeafItem) or indirect references organized as B+tree with name hash used as key (see f2f::format::DirectoryTreeInternalNode and f2f::format::DirectoryTreeLeaf for format of tree nodes).