Historically, it made deletion rather difficult with some problematic edge-cases. You could unlink a directory and create an orphan cycle that would never be deleted. Combine that with race conditions on a multi-user systems, plus the indeterminate cost of cycle-detection, and it turns out to be a rather complex problem to solve properly, and banning hard-links is a very simple way to keep the problem tractable, and result in fast, robust and reliable filesystem operations.
True, I missed that. I suppose with symlinks you have the reverse problem: you can point to deleted filenames and then have broken links. The cycle detection is still an issue though--it has indeterminate complexity and the graph can be modified as you are traversing it!
Historically, it made deletion rather difficult with some problematic edge-cases. You could unlink a directory and create an orphan cycle that would never be deleted. Combine that with race conditions on a multi-user systems, plus the indeterminate cost of cycle-detection, and it turns out to be a rather complex problem to solve properly, and banning hard-links is a very simple way to keep the problem tractable, and result in fast, robust and reliable filesystem operations.
GP was talking about symlink cycles though, which can't produce orphans during deletion.
True, I missed that. I suppose with symlinks you have the reverse problem: you can point to deleted filenames and then have broken links. The cycle detection is still an issue though--it has indeterminate complexity and the graph can be modified as you are traversing it!
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