hack, thereby allowing future extensions to the structure (e.g., for extended
attributes) without rebreaking the ABI. FTSENT now contains a pointer to the
parent stream, which fts_compar() can then take advantage of, avoiding the
undefined behavior previously warned about. As a consequence of this change,
the prototype of the comparison function passed to fts_open() has changed
to reflect the required amount of constness for its use. All callers in the
tree are updated to use the correct prototype.
Comparison functions can now make use of the new parent pointer to access
the new stream-specific private data pointer, which is intended to assist
creation of reentrant library routines which use fts(3) internally.
Not objected to in spirit by: -arch
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