Table of Contents

(BAD) NEWS

I haven't got time to work on frfs any longer.
I focus mainly on my house and my girlfriend, then crosstool-NG and the Toshiba e800 Linux port.

frfs was my first attempt to work with FUSE, and it proved quite easy to create a simple file system. All the complexity does not lie within FUSE, but really within the file system you implement. That was very instructive, and I learnt quite a big deal.
I may resume work on frfs later, though. Should this happen, I hope I will have a better design before I start.




Sorry for those of you who had hope in frfs.


Latest version

Latest frfs version is frfs-0.0.3.

Introduction

With Linux, creating RAM-backed file system is easy: su to root, mount a tmpfs some place, come back to plain user.

Ah, but you've got to become root! I abhor being root when that can be avoided.

The solution is to use the FUSE library and pseudo- file system and let the casual user mount the file system.

frfs is just that: a FUSE-based, in-RAM File System (and no, it does not stand for FRench FileSystem, though I happen to be French).

In its current state, frfs does work quite nicely. It supports most of the usefull features of a Linux file system:

  • files and directories
  • symlinks
  • hard links
  • unlink open files, free on last close()
  • most file operations:
    • open(2)
    • read(2)
    • write(2)
    • close(2)
    • opendir(2)
    • readdir(2)
    • truncate(2)
    • and so on…

But it lacks some functionality: some interesting operations are not yet implemented (but should be easy):

  • statfs(2)
  • flush(2)
  • and so on…
  • extended attributes

Also it is not thread-safe yet. Some infrastructure is there, but code is missing.

Usage

make

  • mount:

./frfs /some/place/frfs

  • use:

cd /some/place/frfs
tar xjf /my/files/linux-2.6.22.3.tar.bz2
cd linux-2.6.22.3
make defconfig
make
cd

  • umount:

fusermount -u /some/place/frfs

WARNING!!!

Versions prior to 0.0.3 are not thread-safe, and don't force single-threaded mode in FUSE. You have to specify the -s option when running frfs, as:

./frfs -s /some/place/frfs

0.0.3 (and above) do not need you specify -s, as they do force it internally.

Prospective work

Here is a list of somewhat ordered TODOs:

  • Make it thread-safe.
  • Make it build on 32-bit archs with debug messages (without debug msg, it's OK).
  • Make the opened file handles table dynamic (how many open file can there be at any one time in a UNIX system?)
  • Unfortunately, it is quite slow. Internal structures are based on chained lists, which is really slow when it comes to big trees (say, a Linux kernel!). There is much work in this area. Some idea come to mind:
    • a cache for recently searched dentries
    • hash-tables (there is a CRC-8-based lookup table in place now)
    • B-trees or red-black-trees
    • use a garbage collector (I don't yet know what for, but I like garbage collectors! :-P )
  • frfs is an in-RAM file system, which means that all data is lost on umount. It could be interesting to have the data written to disk in a compact form (compressed, for example) before actual umount, so it could be retrieved on the next mount. Snapshots would then be easy to implement:
    • send a signal to the file system so it dumps its internal structures onto disk
    • periodic dumps
    • use extended attributes to mark data (not) to be saved on dumps
  • Distribute the file system across a cluster of nodes (Oh yes, I know: I'm dreaming :-) ):
    • centralised model
      • access the same data from whatever machine in the cluster
      • similar to what NFS, samba et al. provide
    • distributed model
      • migrate data between machines, live
        • migrate to the most demanding machine
        • migrate with nodes coming and going
        • migrate for fast access when behind a slow link
      • replicate data in more than one machine, live
        • no loss (or reduced risk of loss) of data
        • replicate for fast access when behind a slow link
        • use extended attributes to mark (un)important or (un)shareable data
projects/frfs.txt · Last modified: 20090914.002147 by ymorin
 
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