Btree directories (Re: Status of HFS+ support)

[flar at allandria.com]

Alexander Viro wrote:
> Shrinking/growing the same directory is not going to happen while you
> are in ->readdir(). You have ->i_zombie on it, so...

That's a bit of a help. The 2.2 docs rarely mentioned what was locked
when, and finding all the various locks in the code wasn't easy.

> 	Urgh. Could you show me your code? I think that a variation of the
> scheme used for fatfs may work here. Basically, you can keep hash of

You can find some of my code at http://devel.linuxppc.org/pub/users/flar/
which is in the form of patches to a slightly old 2.2 kernel. However,
since the patches hardly touch any existing files, it will likely apply
cleanly to any 2.2 kernel. I have some minor changes that aren't there
yet, but nothing that changes the basic outline or actually makes it
work properly. I didn't look much at fatfs because I didn't think it
would be relevant, but I'll take a look now that I have some idea what
I should look for there. My code is based on a mix of code stolen from
ext2 and hfs and a few ideas I thought of on my own.

> directory entries and do (find; unhash; copy; rehash) whenever you move
> one. inodes would keep references to such entries, ditto for readdir
> having a "cursor" entry. Rebalancing would go under rw-semaphore (writer)
> and all tree lookups/scans under the same semaphore (reader). That way you
> can get rid of the tree search in ->write_inode(), BTW.

I'm currently ignoring locking almost entirely, because my support is
read only, but I did have a few ideas on where I would need locking.
Hopefully my code isn't completely wrong, but I'd be happy to accept
any advice on where I really do need to worry about locking. I still
haven't read the latest documentation that I've been told got put
into 2.4 but I also haven't started porting my code to 2.4 for lack
of time.

	Brad Boyer
	flar at pants.nu


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