Compilation
-----------
$ autoreconf -i
$ ./configure
[ get the fuse_kernel.h you have for defining the FUSE protocol and copy it under include ]
$ make
Testing
-------
Folly ships with one example filesystem, an implementation the classic nullfs concept.
After compilation, on Linux it can be run as
$ FUSE_MOUNTPOINT=<mountpoint> [FOLLY_FNODEOPS=(list|rb|hash)] ./app/nully/nully [-d] [<mirror root>]
"-d" implies it printing debug messages, <mirror root> is the path the dir tree
under which shall be mirrored under <mountpoint> when the mount has taken
place.
ATM it neither daemonizes itself, nor unmounts itself upon termination. On
FOLLY_FNODEOPS, see below.
Design
------
Folly is a minimalist lib, as is it knows just very basic information about the
FUSE protocol. It tries to be independent of its revisions, only structures like
fuse_(in|out)_header are used. It doesn't even include the header file defining
the protocol (ie. fuse_kernel.h), you are free to use any version of it.
A struct named "fvfs" is threaded through its operation, the most
interesting part of which are the members "inbuf" and "outbuf". Folly provides a
service loop, which operates as follows:
- reads request from kernel to inbuf
- calls the appropriate callback, based on the optable the loop is initiated
with
- callbacks uniformly take only an fvfs parameter
- the callback is responsible for parsing the request data in inbuf; it's done
as follows: there are auxiliary inline functions provided by folly, like eg.
fuse_req_body, which returns a pointer to the actual payload, which then
should be casted to the appropriate message structure pointer type
as is defined in fuse_kernel.h
- the callback should place the answer to outbuf
- the loop sends outbuf to kernel
- loop :)
Apart from the service loop, folly provides a pluggable infrastructure for
managing the inode tree ("fnode", in folly parlance). The lib itself provides
three kind of nodeops, one called "list", in which child nodes are simply a
linked list, one called "rb", which organizes nodes into a red-black tree, and
one called "hash", which uses a hashing technique for looking up fnodes (which
hashing is the same as in libfuse hi-lib). Users are free to roll their own
nodeops.
In case of the example fs "nully", the nodeop backend can be specified by the
FOLLY_FNODEOPS environment variable.
History
-------
My primary motivation was to write a FUSE based filesystem interface to
FreeBSD's sysctl facility. I realized that I don't need all that infrastructure
which is provided by libfuse, and taking into account that if I plan to create
something which can be included in FreeBSD sometime in the future, I need to
have it BSD licensed -- which libfuse (and projects relying on it) cannot be --
I decided to write my fs from scratch. At some point I've seen the potential
of making the code more generic, so I switched my perspective, and instead of
just writing one fs, I turned it into a new library for FUSE. (The sysctl fs
has not yet been written though...)
Trivia
------
Folly is named after the Pere Ubu song "Folly of Youth". (Oh cruel world,
they have took it off of Youtube :/ )
Have fun,
Csaba Henk