Re: fallocate for FFS

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>>> I will try to figure it out, since its not yet implemented the
>>> syscall is a good way to start dev in BSD kernel.
>> I'm not sure about that; many people have started looking at it and
>> not got anywhere.
> It is true that adding a system call is an easy entry point to learn
> about the kernel.  But here the syscall is the easy part, the real
> work is modifying FFS code to suport it, and that is a steep learning
> curve.

Not just a steep learning curve.  Some of the fallocate operations
(mode zero in particular) would be fairly easy.  But, as someone who
knows somewhat of FFS, I would say some of the operations, in
particular anything that involves allocating space after EOF, would be
rather difficult to implement even for someone who's past the learning
curve.  (Some others, while easy, would be tedious and expensive;
FALLOC_FL_COLLAPSE_RANGE is an example.  While it would technically be
possible to make it fast and simple by taking advantage of the
granularity requirement leeway, such an implementation would be too
restrictive to be worth doing.)

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