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Re: [PATCH 07/23] expire_reflog(): use a lock_file for rewriting the reflog file

From
Jeff King <peff@peff.net>
Date
Dec 9, 2014, 18:54 UTC
Message-ID
<20141209185433.GB31158@peff.net>
In-Reply-To
<xmqqfvcomzib.fsf@gitster.dls.corp.google.com>
On Tue, Dec 09, 2014 at 10:47:24AM -0800, Junio C Hamano wrote:
Show 18 quoted lines
> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
> > This isn't documented very well. I thought I saw a comment somewhere in
> > the code that stated it explicitly, but I can't find it now. In any
> > case, my understanding of the locking protocol for reflogs is:
> >
> >     The reflog for "$refname", which is stored at
> >     "$GIT_DIR/logs/$refname", is locked by holding
> >     "$GIT_DIR/refs/$refname.lock", *even if the corresponding
> >     reference is packed*.
> >
> > This implies that readers, who don't pay attention to locks, have to be
> > prepared for the possibility that the reflog is in the middle of an
> > update and that the last line is incomplete. This is handled by
> > show_one_reflog_ent(), which discards incomplete lines.
> 
> Interesting, as I think I saw Peff did something around that area
> recently.

Yeah, and I had no idea about the truncated-line race which Michael described at the time. It makes me glad that I took the time to do the more careful thing[1] (fixing the reverse-reflog parser to properly include the newline when present) and not the quick-and-easy thing[2] (teaching show_one_reflog_ent to accept entries without newlines).

What you have queued in jk/for-each-reflog-ent-reverse should be fine, even in light of what Michael said.

-Peff
[1] http://article.gmane.org/gmane.comp.version-control.git/260849
[2] http://article.gmane.org/gmane.comp.version-control.git/260807
Previous: Junio C HamanoNext: Stefan Beller
Message 20 of 63 in “Add reflog_expire() to the references API”
  1. 00/23 Add reflog_expire() to the references APIMichael Haggerty, Dec 4, 2014
  2. 01/23 refs.c: make ref_transaction_create a wrapper for ref_transaction_updateMichael Haggerty, Dec 4, 2014
  3. 02/23 refs.c: make ref_transaction_delete a wrapper for ref_transaction_updateMichael Haggerty, Dec 4, 2014
  4. 03/23 refs.c: add a function to append a reflog entry to a fdMichael Haggerty, Dec 4, 2014
  5. 04/23 expire_reflog(): remove unused parameterMichael Haggerty, Dec 4, 2014
  6. Jonathan NiederDec 4, 2014
  7. Jonathan NiederDec 4, 2014
  8. Michael HaggertyDec 5, 2014
  9. 05/23 expire_reflog(): rename "ref" parameter to "refname"Michael Haggerty, Dec 4, 2014
  10. Jonathan NiederDec 4, 2014
  11. 06/23 expire_reflog(): exit early if the reference has no reflogMichael Haggerty, Dec 4, 2014
  12. Jonathan NiederDec 4, 2014
  13. Jonathan NiederDec 4, 2014
  14. Michael HaggertyDec 5, 2014
  15. 07/23 expire_reflog(): use a lock_file for rewriting the reflog fileMichael Haggerty, Dec 4, 2014
  16. Jonathan NiederDec 5, 2014
  17. Stefan BellerDec 5, 2014
  18. Michael HaggertyDec 8, 2014
  19. Junio C HamanoDec 9, 2014
  20. Jeff KingDec 9, 2014
  21. Stefan BellerDec 5, 2014
  22. Junio C HamanoDec 5, 2014
  23. Stefan BellerDec 5, 2014
  24. Junio C HamanoDec 5, 2014
  25. Michael HaggertyDec 8, 2014
  26. ronnie sahlbergDec 5, 2014
  27. Michael HaggertyDec 8, 2014
  28. 08/23 Extract function should_expire_reflog_ent()Michael Haggerty, Dec 4, 2014
  29. Stefan BellerDec 8, 2014
  30. 09/23 expire_reflog(): extract two policy-related functionsMichael Haggerty, Dec 4, 2014
  31. Stefan BellerDec 5, 2014
  32. 10/23 expire_reflog(): add a "flags" argumentMichael Haggerty, Dec 4, 2014
  33. Stefan BellerDec 8, 2014
  34. 11/23 expire_reflog(): move dry_run to flags argumentMichael Haggerty, Dec 4, 2014
  35. Stefan BellerDec 8, 2014
  36. 12/23 expire_reflog(): move updateref to flags argumentMichael Haggerty, Dec 4, 2014
  37. Stefan BellerDec 8, 2014
  38. 13/23 Rename expire_reflog_cb to expire_reflog_policy_cbMichael Haggerty, Dec 4, 2014
  39. Stefan BellerDec 8, 2014
  40. 14/23 struct expire_reflog_cb: a new callback data typeMichael Haggerty, Dec 4, 2014
  41. Stefan BellerDec 8, 2014
  42. 15/23 expire_reflog(): pass flags through to expire_reflog_ent()Michael Haggerty, Dec 4, 2014
  43. Stefan BellerDec 8, 2014
  44. 16/23 expire_reflog(): move verbose to flags argumentMichael Haggerty, Dec 4, 2014
  45. Stefan BellerDec 8, 2014
  46. 17/23 expire_reflog(): move rewrite to flags argumentMichael Haggerty, Dec 4, 2014
  47. Stefan BellerDec 8, 2014
  48. 18/23 Move newlog and last_kept_sha1 to "struct expire_reflog_cb"Michael Haggerty, Dec 4, 2014
  49. Stefan BellerDec 8, 2014
  50. 19/23 expire_reflog(): treat the policy callback data as opaqueMichael Haggerty, Dec 4, 2014
  51. Stefan BellerDec 8, 2014
  52. 20/23 reflog_expire(): new function in the reference APIMichael Haggerty, Dec 4, 2014
  53. Stefan BellerDec 8, 2014
  54. Michael HaggertyDec 12, 2014
  55. Jeff KingDec 12, 2014
  56. Junio C HamanoDec 12, 2014
  57. 21/23 refs.c: remove unlock_ref/close_ref/commit_ref from the refs apiMichael Haggerty, Dec 4, 2014
  58. 22/23 lock_any_ref_for_update(): inline functionMichael Haggerty, Dec 4, 2014
  59. Stefan BellerDec 8, 2014
  60. Michael HaggertyDec 11, 2014
  61. 23/23 refs.c: don't expose the internal struct ref_lock in the header fileMichael Haggerty, Dec 4, 2014
  62. Junio C HamanoDec 4, 2014
  63. Stefan BellerDec 5, 2014

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