linux-kernel - Re: [RFC] B+Tree library

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Date:	Fri, 31 Oct 2008 16:35:40 +0100
From:	Jörn Engel <joern@...fs.org>
To:	Tim Gardner <tcanonical@....com>
Cc:	Johannes Berg <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] B+Tree library

On Fri, 31 October 2008 09:18:06 -0600, Tim Gardner wrote:
> Johannes Berg wrote:
> >> +static inline size_t btree_visitorl(struct btree_headl *head, long opaque,
> >> +		visitorl_t func2)
> >> +{
> >> +	return btree_visitor(&head->h, &btree_geo32, opaque, visitorl, func2);
> >> +}
> > 
> > Incidentally, do you think it would be possible to implement a kind of 
> > 
> > btree_for_each_entry(e, ...) {
> > 	do something with e
> > }
> > 
> > macro or function/macro combination? You seem to be doing a recursive
> > walk across the tree, would it be useful to have a linked list at the
> > lowest level of nodes to be able to iterate more easily?
> 
> What would you expect to be the behavior if you remove 'e' ? That might
> cause the tree to get re-ordered. Do you restart the list traversal?

BUG(), if you're lucky.  Silent data corruption, if you're not so lucky.

The btree_grim_visitor() exists to remove all element after being handed
to the visitor.  btree_visitor() removes none.  Either function requires
the caller to do proper locking.  Calling two functions from two threads
in parallel or calling a function from the visitor callback will give
you undefined results - with the exception of parallel lookups, which
are obviously fine.

Jörn

-- 
Beware of bugs in the above code; I have only proved it correct, but
not tried it.
-- Donald Knuth
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