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SubjectRe: hfs support for blocksize != 512
Hi,

> > hfs. For example reading from a file might require a read from a btree
> > file (extent file), with what another file write can be busy with (e.g.
> > reordering the btree nodes).
>
> And?

The point is: the thing I like about Linux is its simple interfaces, it's
the basic idea of unix - keep it simple. That is true for most parts - the
basic idea is simple and the real complexity is hidden behind it. But
that's currently not true for vfs interface, a fs maintainer has to fight
right now with fscking complex vfs interface and with a possible fscking
complex fs implementation. E2fs or affs have a pretty simple structure and
I believe you that it's not that hard to fix, maybe there is also a simple
solution for hfs. But I'd like you to forget about that and think about
the big picture (how Linus nicely states it). What we should aim at with
the vfs interface is simplicity, I want to use a fscking simple semaphore
to protect something like anywhere else, I don't want to juggle with lots
blocks wich have to be updated atomically. Maybe you get once right, but
it will follow you as a nightmare, you add one feature (e.g. quota), you
add another feature (like btrees), you so still damned fscking sure to get
and keeping it right?
So and? What I'd really like to see from you is to be a bit more
supportive for other peoples problems, I really don't expect you to solve
these problems, but if someone approaches a different solution, you're
pretty quick to refuse it.
So lets get back to the vfs interface, fs currently have to do pretty much
all there changes atomically, they have to grab all the buffers they need
and do all changes at once. How can you be sure that this is possible for
every possible fs? How do you make sure you don't create other problems
like livelocks? We currently have problem that things like kswapd require
an asynchronous interface, but fs prefer to synchronize it. Currently you
pushing all the burden of an asynchronous interface into the fs, which
want to rather avoid that. Why don't you think for a moment in the other
direction? Currently I'm playing with the idea of a kernel thread for
asynchronous io (maybe one per fs), that thread takes the io requests e.g.
from kswapd and the io thread can safely sleep on it, while kswapd can
continue its job, but I don't know yet, where to put, whether in the fs
specific part or whether it can be made generic enough to be put into the
generic part. Can we please think for a moment in that direction? At some
point you have to synchronize the io anyway (at latest when it hits the
device), but I would pretty much prefer if a fs would get some help at
some earlier point.
(Anyway, I need some sleep now as well... :) )

bye, Roman

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