On Sat, Sep 14, 2013 at 11:22 AM, Nicolas Pitre <n...@fluxnic.net> wrote:
> The cache is currently updated by the caller.  The caller may ask for a
> copy of 2 entries from a base object, but that base object may itself
> copy those objects from somewhere else in a larger chunk.
> Let's consider this example:
> tree A
> ------
> 0 (0) copy 2 entries from tree B starting at entry 0
> 1 (2) copy 1 entry from tree B starting at entry 3
> tree B
> ------
> 0 (0) copy 6 entries from tree C starting at entry 0
> 1 (6) entry "foo.txt"
> 2 (7) entry "bar.txt"
> Right now, the code calls decode_entries() to decode 2 entries from tree
> B but those entries are part of a copy from tree C.  When that call
> returns, the cache is updated as if tree B entry #2 would start at
> offset 1 but this is wrong because offset 0 in tree B covers 6 entries
> and therefore offset 1 is for entry #6.
> So this needs a rethink.

I've given it some thought and see no simple/efficient way do it when
2+ depth is involved. Ideally tree A should refer to tree C directly
for the first two entries, but in general we can't enforce that a copy
sequence must refer to non-copy sequences only. Caching flattened tree
B up until the 6th entry may help, but then there's no need to cache
offsets anymore because we could just cache tree A..
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