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Re: [IGNORETHIS/PATCH] Choosing the sha1 prefix of your commits

From
Junio C Hamano <gitster@pobox.com>
Date
Oct 20, 2011, 06:57 UTC
Message-ID
<7vr5289mlu.fsf@alter.siamese.dyndns.org>
In-Reply-To
<20111020043448.GA7628@sigill.intra.peff.net>
Jeff King <peff@peff.net> writes:
> Agreed. Having hidden cruft makes birthday collision attacks easier (or
> it will, if sha1 ever gets broken to that point).  Unfortunately, there
> is a _ton_ of code which assumes that commit messages are
> NUL-terminated, as they always have been since e871b64 (2005-05-25).

I think that commit is irrelevant, as long as read_sha1_file() returns the contents as <ptr,len> pair, which has been the case forever. It's just the matter of propagating the length back up the callchain.

A naïve implementation to add "len" member to struct commit would increase the size of the in-core commit object by sizeof(unsigned long), which we may want to avoid. Traversals that care nothing but the topology of the history would have to waste that memory and these things tend to add up (8-byte ulong * 250k commits = 2MB).

Perhaps change the type of "buf" member in struct commit to a pointer to a <ptr,len> pair, or something? Or perhaps a few megabytes wasted between friends we do not care much about?

Previous: Jeff KingNext: Jeff King
Message 12 of 24 in “Choosing the sha1 prefix of your commits”
  1. Choosing the sha1 prefix of your commitsÆvar Arnfjörð Bjarmason, Oct 19, 2011
  2. Jeff KingOct 19, 2011
  3. Jeff KingOct 19, 2011
  4. Jeff KingOct 20, 2011
  5. Kyle MoffettOct 20, 2011
  6. Jeff KingOct 20, 2011
  7. Junio C HamanoOct 20, 2011
  8. Kyle MoffettOct 20, 2011
  9. Jeff KingOct 24, 2011
  10. Junio C HamanoOct 20, 2011
  11. Jeff KingOct 20, 2011
  12. Junio C HamanoOct 20, 2011
  13. Jeff KingOct 20, 2011
  14. Ted Ts'oOct 20, 2011
  15. Jeff KingOct 20, 2011
  16. Drew NorthupOct 25, 2011
  17. Re* [IGNORETHIS/PATCH] Choosing the sha1 prefix of your commitsJunio C Hamano, Oct 20, 2011
  18. Jeff KingOct 20, 2011
  19. Nguyen Thai Ngoc DuyOct 20, 2011
  20. Nguyen Thai Ngoc DuyOct 20, 2011
  21. Jeff KingOct 20, 2011
  22. Mikael MagnussonOct 20, 2011
  23. Elijah NewrenOct 20, 2011
  24. Jonathan NiederOct 19, 2011

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