On Mon, 2005-10-10 at 22:35 +0100, Nick wrote:
> Hi
> 
> I note from emails last May (with Coudene Nicolas) you developed unionsfs
> not from a union.fist file but from a base0fs.fist generated base which was
> then hand crafted. You suggested that any similar venture might take the
> same route and use the unionfs sources as a learning reference. 
> 
> On this matter, is there any more documentation to help us to interpret the
> source code in particular an overall strategy? 11,000 lines of C makes
> fairly dry reading! To get a scale of the task, have you any idea of how
> much work unionfs represents. It looks considerable as the credits for
> main.c covers 2003-05 with 7 names.
Yes it was a considerable effort to get it to work, then to get it to
work properly, to plug races incompletely, stabilize it to some degree,
learn about corner cases, etc.  Those seven names don't actually reflect
all the effort that has gone into the code: in recent months may people
have helped us by finding bugs, testcases, and posting patches.

And of course, the effort continues.

That being said, not all 7 people worked on the code at any one time.
Two of them worked on it for a while, then added two more, then dropped
the original two, then added one more, and another more.  And Dr. Zadok
wrote the original templates, but for Unionfs (mostly) didn't work on
the code, but rather higher level design and "spiritual guidance."

As far as understanding the operation of Unionfs, the best place to
start is our TOS Journal article available from:
http://www.fsl.cs.sunysb.edu/project-unionfs.html

If you wanted to start over, you would have to ask yourself what set of
features do you want to implement.   Some important things that will
determine that are:
1. Do you want to handle rw+ro branches, or just rw (or just ro, or a
single rw and many ro)?
2. How much copy-on-write do you want to do?
3. Should the branch configuration be mutable (i.e., do you decide it on
mount or can you dynamically add/remove branches)?

Charles

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