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SubjectRe: hfs support for blocksize != 512
On Tue, 29 Aug 2000, Tony Mantler wrote:

> (Obligitory disclaimer: QNX is an embedded operating system, both it's
> architecture and target market is considerably different from Linux's)
>
> QNX's filesystem interfaces make it so painfully easy to write a filesystem
> that it puts everything else to shame. You can easily write a fully
> functioning, race-free, completely coherent filesystem in less than a week,
> it's that simple.

I'd interject that it's not a very fair comparison between the kernel
complexity of an RTOS and a full fledged traditional OS, but go on....
;-)


> Now, let's say you do an 'ls' on the FOO directory. The FS api would tap
> your filesystem on the shoulder and ask "Hey you, what's in the FOO
> directory?". Your filesystem would reply "BAR and BAZ".

It might also reply with a stat structure, depending on the
implementation, but otherwise, yeah, this is a good model to move towards.


> So what does it all mean? Basically, if you want hugely complex dentries,
> and inodes as big as your head, you can do that. If you don't, more power
> to you. It's all entirely contained inside your specific FS code, the FS
> api doesn't care one bit. It just asks you for files.

Indeed, that's what a VFS layer should do -- abstract away all physical
structure, inodes, etc., leaving only the file abstraction. I've read
that the BSD-derived OSes have vnode interfaces that are remarkably
similar to what you're describing, i.e. the concept isn't restricted to
RTOSes.

Note that I haven't touched the Linux VFS layer since 2.0.xx, so I'm not
in a position to comment on the current state of the code. :-)


Later,
David

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