This is an initial implementation of ChunkFS technique, briefly discussedat: http://lwn.net/Articles/190222 and http://cis.ksu.edu/~gud/docs/chunkfs-hotdep-val-arjan-gud-zach.pdf
This implementation is done within ext2 driver. Every chunk is an independent ext2 file system. The knowledge about chunks is kept within ext2 and 'continuation inodes', which are used to allow files and directories span across multiple chunks, are managed within ext2.
At mount time, super blocks for all the chunks are created and linked with the global super_blocks list maintained by VFS. This allows independent behavior or individual chunks and also helps writebacks to happen seamlessly.
Apart from this, chunkfs code in ext2 effectively only provides knowledge of:- what inode's which block number to look for, for a given file's logical block number
- in which chunk to allocate next inode / block - number of inodes to scan when a directory is being readTo maintain the ext2's inode number uniqueness property, 8 msb bits of inode number are used to indicate the chunk number in which it resides.
As said, this is a preliminary implementation and lots of changes are expected before this code is even sanely usable. Some known issues and obvious optimizations are listed in the TODO file in the chunkfs patch.
http://cis.ksu.edu/~gud/patches/chunkfs-v0.0.8.patch - one big patch - applies to 2.6.18 Attached - ext2-chunkfs-diff.patch.gz - since the code is a spin-off of ext2, this patch explains better what has changed from the ext2. git://cislinux.cis.ksu.edu/chunkfs-tools - mkfs, and fsck for chunkfs. http://cis.ksu.edu/~gud/patches/config-chunkfs-2.6.18-uml - config file used; tested mostly on UML with loopback file systems.NOTE: No xattrs and xips yet, CONFIG_EXT2_FS_XATTR and CONFIG_EXT2_FS_XIP should be "no" for clean compile.
Please comment, suggest, criticize. Patches most welcome. Best, AG -- May the source be with you. http://www.cis.ksu.edu/~gud
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