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Re: [PATCH 2/5] pack-bitmap: tag bitmapped packs with their corresponding MIDX

From
Junio C Hamano <gitster@pobox.com>
Date
Aug 28, 2024, 00:14 UTC
Message-ID
<xmqqplpt5wrt.fsf@gitster.g>
In-Reply-To
<1838bbcf7fe6daa58a7db78b81a2d08138fe176e.1724793201.git.me@ttaylorr.com>
Taylor Blau <me@ttaylorr.com> writes:
Show 28 quoted lines
> The next commit will need to use the bitmap's MIDX (if one exists) to
> translate bit positions into pack-relative positions in the source pack.
>
> Ordinarily, we'd use the "midx" field of the bitmap_index struct. But
> since that struct is defined within pack-bitmap.c, and our caller is in
> a separate compilation unit, we do not have access to the MIDX field.
>
> Instead, add a "from_midx" field to the bitmapped_pack structure so that
> we can use that piece of data from outside of pack-bitmap.c. The caller
> that uses this new piece of information will be added in the following
> commit.
>
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  midx.c        | 1 +
>  pack-bitmap.c | 1 +
>  pack-bitmap.h | 1 +
>  3 files changed, 3 insertions(+)
>
> diff --git a/midx.c b/midx.c
> index ca98bfd7c6..67e0d64004 100644
> --- a/midx.c
> +++ b/midx.c
> @@ -496,6 +496,7 @@ int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
>  				 MIDX_CHUNK_BITMAPPED_PACKS_WIDTH * local_pack_int_id +
>  				 sizeof(uint32_t));
>  	bp->pack_int_id = pack_int_id;
> +	bp->from_midx = m;

Do multi_pack_index objects live as long as bitmapped_pack objects that point at them live? If m later goes away without letting the bitmapped_pack know about it, the borrowed pointer in from_midx would become dangling, which is not what we want to see.

"None of these objects are released or relocated while we are running pack-objects, so once the .from_midx member is assigned here, it will always be pointing at a valid multi_pack_index object" is a satisfactory answer, I guess.

Previous: Taylor BlauNext: Taylor Blau
Message 4 of 17 in “pack-objects: brown-paper-bag fixes for multi-pack reuse”
  1. 0/5 pack-objects: brown-paper-bag fixes for multi-pack reuseTaylor Blau, Aug 27, 2024
  2. 1/5 t/t5332-multi-pack-reuse.sh: verify pack generation with --strictTaylor Blau, Aug 27, 2024
  3. 2/5 pack-bitmap: tag bitmapped packs with their corresponding MIDXTaylor Blau, Aug 27, 2024
  4. Junio C HamanoAug 28, 2024
  5. Taylor BlauAug 29, 2024
  6. Jeff KingSep 5, 2024
  7. Taylor BlauSep 17, 2024
  8. 3/5 builtin/pack-objects.c: translate bit positions during pack-reuseTaylor Blau, Aug 27, 2024
  9. Junio C HamanoSep 4, 2024
  10. 4/5 pack-bitmap.c: avoid repeated `pack_pos_to_offset()` during reuseTaylor Blau, Aug 27, 2024
  11. Junio C HamanoSep 4, 2024
  12. Taylor BlauSep 4, 2024
  13. 5/5 builtin/pack-objects.c: do not open-code `MAX_PACK_OBJECT_HEADER`Taylor Blau, Aug 27, 2024
  14. Junio C HamanoSep 4, 2024
  15. Taylor BlauSep 4, 2024
  16. Jeff KingSep 5, 2024
  17. Junio C HamanoSep 5, 2024

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