Filestore is a basic Chord application that can store and retrieve

files from a Chord ring. It demonstrates how to use DHash to store

blocks, and how to program in the style needed by libasync.

technical details

The file storage format is fairly simple. Files are split up into

16,384-byte "data blocks." They are stored in DHash as content-hash

blocks. "Inode blocks" contain the file's name and length, and a list

of hashes for "indirect blocks." The indirect blocks contain a list of

hashes for the file's data blocks. The file is identified by the hash

of the inode block.

This simple, fixed, three-layer scheme permits files up to

10,815,307,776 bytes. For files smaller than 16,384 bytes, it has an

overhead of one inode block of 280 bytes, and one indirect block of 20

bytes. The users can view the filename and file length before

attempting to retrieve the file, so they can avoid retrieving files

that are larger than they want.

Examples of use:

storing a file:

> ./filestore ../lsd/csock -s some_file

e34cb4fa86a073f390b224f637b90db88f82db06

listing inode info:

> ./filestore ../lsd/csock -l e34cb4fa86a073f390b224f637b90db88f82db06

some_file: 19463682 bytes

fetching a file:

> ./filestore ../lsd/csock -f e34cb4fa86a073f390b224f637b90db88f82db06

todo:

better documentation

throttling of insert/retrieve requests?