Back in 32f3c541e3 (multi-pack-index: write pack names in chunk, 2018-07-12)
the MIDX's "Packfile Names" (or "PNAM", for short) chunk was described
as containing an array of string entries. e0d1bcf825 notes that this is
the only chunk in the MIDX format's specification that is not guaranteed
to be 4-byte aligned, and so should be placed last.
This isn't quite accurate: the entries within the PNAM chunk are not
guaranteed to be aligned since they are arbitrary strings, but the
chunk itself is aligned since the ending is padded with NUL bytes.
That external padding has always been there since 32f3c541e3 via
midx.c::write_midx_pack_names(), which ended with:
i = MIDX_CHUNK_ALIGNMENT - (written % MIDX_CHUNK_ALIGNMENT)
if (i < MIDX_CHUNK_ALIGNMENT) {
unsigned char padding[MIDX_CHUNK_ALIGNMENT];
memset(padding, 0, sizeof(padding))
hashwrite(f, padding, i);
written += i;
}
In fact, 32f3c541e3's log message itself describes the chunk in its
first paragraph with:
Since filenames are not well structured, add padding to keep good
alignment in later chunks.
So these have always been externally aligned. Correct the corresponding
part of our documentation to reflect that.
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
Documentation/gitformat-pack.txt | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/Documentation/gitformat-pack.txt b/Documentation/gitformat-pack.txt
index d7153962d4..54000c9412 100644
--- a/Documentation/gitformat-pack.txt
+++ b/Documentation/gitformat-pack.txt
@@ -392,8 +392,9 @@ CHUNK DATA:
Packfile Names (ID: {'P', 'N', 'A', 'M'})
Stores the packfile names as concatenated, NUL-terminated strings.
Packfiles must be listed in lexicographic order for fast lookups by
- name. This is the only chunk not guaranteed to be a multiple of four
- bytes in length, so should be the last chunk for alignment reasons.
+ name. Individual entries in this chunk are not guarenteed to be
+ aligned. The chunk is externally padded with zeros to align
+ remaining chunks.
OID Fanout (ID: {'O', 'I', 'D', 'F'})
The ith entry, F[i], stores the number of OIDs with first
--
2.42.0.349.gf0c1128f8b.dirty
