There has been great hue and cry over the recently found "URL exploits" in Mac OS X. I briefly looked at this issue today. While it's certainly a worrisome situation, in my opinion there seems to be more confusion than necessary (which amounts to a very normal situation in such cases!)
I have a few things to add to what has already been discussed to death in countless places.
I am making a version of hfsdebug available for Jaguar. Note this is only for the possible benefit of those who *must* try this out on Jaguar. Please do not send me any bug/problem reports about this version, even if it does not work at all.
hfsdebug can go through the volume allocation bitmap and calculate a list of free extents, along with their sizes, on a volume. Thus, you could determine the size(s) of the largest free space chunk(s) on your volume. A popular name for this appears to be "free space fragmentation".
Although hsfdebug could quantify free space fragmentation earlier, I did not add an option to print this list out. The newest version of hfsdebug supports the -0 option for this purpose. Please refer to Fragmentation in HFS Plus Volumes (updated) for more details.
I had been wondering for a while as to how well the combination of Panther and HFS+ stands up to fragmentation. According to Apple, there should be so little fragmentation in a typical use-case scenario that you don't even need to worry about it. I have seen several discussions on this topic in the Mac Universe, with many poeple questioning if things were really so good. My seat-of-the-pants opinion coincided with Apple's claims, but I wanted to quantify these things for myself (and for the benefit of others).
Fragmentation in HFS Plus Volumes is a brief analytical look at this issue. The HFS+ volumes that I sampled actually fared somewhat better than what I was expecting.
In this process, I created a tool to peek inside HFS+ -- a filesystem debugger of sorts, which I am calling hfsdebug. I am making hfsdebug available for download in binary form, with a source release due at some point in the future.