We checked old kernels, and old e2fsprogs, and didn't see any cases
where fast (<= 60 chars) symlinks were created using external blocks.
It seems that _something_ did create them, and it would be good to
figure that out so we can determine if it is a widespread problem

I assume it was the original kernel. 

I think e2fsck can fix this quite easily, and there really isn't
an easy way to revert to the old method if the large xattr feature
is enabled.  If you are willing to run a new kernel, you should also
be willing to run a new e2fsck.

It's obviously not enabled on ext3.

We could probably add a fallback to the old mechanism (and print
a one-time warning to upgrade to a newer e2fsck) if an external fast
symlink is found and the large xattr  feature is not enabled, which
would give more time to fix this (hopefully rare in the wild) case.

If the old kernel created it, then likely all the
/lib{,64}/ld-linux.so.2 symlinks have that, which breaks all ELF 
executables. I suspect in these old file systems it's not particularly rare.

So I don't think you can just break them all.

I think it's ok to only handle it when the large xattrs are disabled.

Requiring new e2fsck on old systems is a bad idea.

-Andi