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Re: [PATCH] packed_ref_store: handle a packed-refs file that is a symlink

From
Jeff King <peff@peff.net>
Date
Jul 27, 2017, 18:28 UTC
Message-ID
<20170727182854.wxjvjs2x746n3x2t@sigill.intra.peff.net>
In-Reply-To
<xmqq8tj9okzv.fsf@gitster.mtv.corp.google.com>
On Thu, Jul 27, 2017 at 10:19:48AM -0700, Junio C Hamano wrote:
Show 16 quoted lines
> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
> > Change `commit_packed_refs()` to use `get_locked_file_path()` to find
> > the path of the file that it should overwrite. Since that path was
> > properly resolved when the lockfile was created, this restores the
> > pre-42dfa7ecef behavior.
> 
> Because when we take a lock hold_lock_file() eventually calls into
> lock_file() which by default takes the lock on the target of the
> symbolic link (which is the sensible default, which is triggered in
> this codepath), so this change to use the name of that file is all
> that is needed.
> 
> Makes sense.  Makes me wonder why we need a separate .new file
> (instead of writing into the .lock instead), but that is a different
> issue.

It comes from 42dfa7ece (commit_packed_refs(): use a staging file separate from the lockfile, 2017-06-23). That commit explains that we want to be able to put the new contents into service before we release the lock. But it doesn't say why that's useful.

I recall from past discussions that this will help close some races, and e5cc7d7d2 (repack_without_refs(): don't lock or unlock the packed refs, 2017-07-01) alludes to this. I think the races in question have to do with holding the packed-refs lock while pruning the just-packed files, but I'm having trouble digging up specifics in the archive.

-Peff
Previous: Junio C HamanoNext: Junio C Hamano
Message 40 of 52 in “Create a reference backend for packed refs”
  1. 00/30 Create a reference backend for packed refsMichael Haggerty, Jul 1, 2017
  2. 01/30 t1408: add a test of stale packed refs covered by loose refsMichael Haggerty, Jul 1, 2017
  3. 03/30 packed_ref_store: new structMichael Haggerty, Jul 1, 2017
  4. 04/30 packed_ref_store: move `packed_refs_path` hereMichael Haggerty, Jul 1, 2017
  5. 02/30 add_packed_ref(): teach function to overwrite existing refsMichael Haggerty, Jul 1, 2017
  6. 06/30 clear_packed_ref_cache(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  7. 05/30 packed_ref_store: move `packed_refs_lock` member hereMichael Haggerty, Jul 1, 2017
  8. 09/30 get_packed_refs(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  9. 07/30 validate_packed_ref_cache(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  10. 12/30 commit_packed_refs(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  11. 08/30 get_packed_ref_cache(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  12. 10/30 add_packed_ref(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  13. 11/30 lock_packed_refs(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  14. 16/30 packed_peel_ref(): new function, extracted from `files_peel_ref()`Michael Haggerty, Jul 1, 2017
  15. 15/30 repack_without_refs(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  16. 14/30 get_packed_ref(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  17. 17/30 packed_ref_store: support iterationMichael Haggerty, Jul 1, 2017
  18. 19/30 packed-backend: new module for handling packed referencesMichael Haggerty, Jul 1, 2017
  19. 18/30 packed_read_raw_ref(): new function, replacing `resolve_packed_ref()`Michael Haggerty, Jul 1, 2017
  20. 22/30 commit_packed_refs(): use a staging file separate from the lockfileMichael Haggerty, Jul 1, 2017
  21. 20/30 packed_ref_store: make class into a subclass of `ref_store`Michael Haggerty, Jul 1, 2017
  22. 13/30 rollback_packed_refs(): take a `packed_ref_store *` parameterMichael Haggerty, Jul 1, 2017
  23. 23/30 packed_refs_lock(): function renamed from lock_packed_refs()Michael Haggerty, Jul 1, 2017
  24. 28/30 repack_without_refs(): don't lock or unlock the packed refsMichael Haggerty, Jul 1, 2017
  25. 29/30 t3210: add some tests of bogus packed-refs file contentsMichael Haggerty, Jul 1, 2017
  26. 26/30 clear_packed_ref_cache(): don't protest if the lock is heldMichael Haggerty, Jul 1, 2017
  27. 30/30 read_packed_refs(): die if `packed-refs` contains bogus dataMichael Haggerty, Jul 1, 2017
  28. 27/30 commit_packed_refs(): remove call to `packed_refs_unlock()`Michael Haggerty, Jul 1, 2017
  29. 21/30 commit_packed_refs(): report errors rather than dyingMichael Haggerty, Jul 1, 2017
  30. 25/30 packed_refs_unlock(), packed_refs_is_locked(): new functionsMichael Haggerty, Jul 1, 2017
  31. 24/30 packed_refs_lock(): report errors via a `struct strbuf *err`Michael Haggerty, Jul 1, 2017
  32. Jeff KingJul 5, 2017
  33. Stefan BellerJul 20, 2017
  34. Jonathan NiederJul 20, 2017
  35. packed_ref_store: handle a packed-refs file that is a symlinkMichael Haggerty, Jul 26, 2017
  36. Stefan BellerJul 27, 2017
  37. Jonathan NiederJul 27, 2017
  38. Michael HaggertyJul 27, 2017
  39. Junio C HamanoJul 27, 2017
  40. Jeff KingJul 27, 2017
  41. Junio C HamanoJul 27, 2017
  42. Michael HaggertyJul 28, 2017
  43. Ævar Arnfjörð BjarmasonMay 31, 2021
  44. Jeff KingJun 3, 2021
  45. t: use portable wrapper for readlink(1)Jeff King, Jun 3, 2021
  46. Ævar Arnfjörð BjarmasonJun 4, 2021
  47. Felipe ContrerasJun 3, 2021
  48. Jeff KingJun 3, 2021
  49. Felipe ContrerasJun 3, 2021
  50. Ævar Arnfjörð BjarmasonJun 4, 2021
  51. Felipe ContrerasJun 5, 2021
  52. Ævar Arnfjörð BjarmasonJun 4, 2021

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