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commit-graph: prepare for commit-graph chains

To prepare for a chain of commit-graph files, augment the
commit_graph struct to point to a base commit_graph. As we load
commits from the graph, we may actually want to read from a base
file according to the graph position.

The "graph position" of a commit is given by concatenating the
lexicographic commit orders from each of the commit-graph files in
the chain. This means that we must distinguish two values:

 * lexicographic index : the position within the lexicographic
   order in a single commit-graph file.

 * graph position: the position within the concatenated order
   of multiple commit-graph files

Given the lexicographic index of a commit in a graph, we can
compute the graph position by adding the number of commits in
the lower-level graphs. To find the lexicographic index of
a commit, we subtract the number of commits in lower-level graphs.

While here, change insert_parent_or_die() to take a uint32_t
position, as that is the type used by its only caller and that
makes more sense with the limits in the commit-graph format.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
tags/v2.23.0-rc0
Derrick Stolee Junio C Hamano 5 months ago
parent
commit
d4f4d60f6d
2 changed files with 81 additions and 11 deletions
  1. +78
    -11
      commit-graph.c
  2. +3
    -0
      commit-graph.h

+ 78
- 11
commit-graph.c View File

@@ -359,9 +359,18 @@ int generation_numbers_enabled(struct repository *r)
return !!first_generation;
}

static void close_commit_graph_one(struct commit_graph *g)
{
if (!g)
return;

close_commit_graph_one(g->base_graph);
free_commit_graph(g);
}

void close_commit_graph(struct raw_object_store *o)
{
free_commit_graph(o->commit_graph);
close_commit_graph_one(o->commit_graph);
o->commit_graph = NULL;
}

@@ -371,18 +380,38 @@ static int bsearch_graph(struct commit_graph *g, struct object_id *oid, uint32_t
g->chunk_oid_lookup, g->hash_len, pos);
}

static void load_oid_from_graph(struct commit_graph *g,
uint32_t pos,
struct object_id *oid)
{
uint32_t lex_index;

while (g && pos < g->num_commits_in_base)
g = g->base_graph;

if (!g)
BUG("NULL commit-graph");

if (pos >= g->num_commits + g->num_commits_in_base)
die(_("invalid commit position. commit-graph is likely corrupt"));

lex_index = pos - g->num_commits_in_base;

hashcpy(oid->hash, g->chunk_oid_lookup + g->hash_len * lex_index);
}

static struct commit_list **insert_parent_or_die(struct repository *r,
struct commit_graph *g,
uint64_t pos,
uint32_t pos,
struct commit_list **pptr)
{
struct commit *c;
struct object_id oid;

if (pos >= g->num_commits)
die("invalid parent position %"PRIu64, pos);
if (pos >= g->num_commits + g->num_commits_in_base)
die("invalid parent position %"PRIu32, pos);

hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
load_oid_from_graph(g, pos, &oid);
c = lookup_commit(r, &oid);
if (!c)
die(_("could not find commit %s"), oid_to_hex(&oid));
@@ -392,7 +421,14 @@ static struct commit_list **insert_parent_or_die(struct repository *r,

static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
{
const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
const unsigned char *commit_data;
uint32_t lex_index;

while (pos < g->num_commits_in_base)
g = g->base_graph;

lex_index = pos - g->num_commits_in_base;
commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;
item->graph_pos = pos;
item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
}
@@ -405,10 +441,25 @@ static int fill_commit_in_graph(struct repository *r,
uint32_t *parent_data_ptr;
uint64_t date_low, date_high;
struct commit_list **pptr;
const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
const unsigned char *commit_data;
uint32_t lex_index;

item->object.parsed = 1;
while (pos < g->num_commits_in_base)
g = g->base_graph;

if (pos >= g->num_commits + g->num_commits_in_base)
die(_("invalid commit position. commit-graph is likely corrupt"));

/*
* Store the "full" position, but then use the
* "local" position for the rest of the calculation.
*/
item->graph_pos = pos;
lex_index = pos - g->num_commits_in_base;

commit_data = g->chunk_commit_data + (g->hash_len + 16) * lex_index;

item->object.parsed = 1;

item->maybe_tree = NULL;

@@ -452,7 +503,18 @@ static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uin
*pos = item->graph_pos;
return 1;
} else {
return bsearch_graph(g, &(item->object.oid), pos);
struct commit_graph *cur_g = g;
uint32_t lex_index;

while (cur_g && !bsearch_graph(cur_g, &(item->object.oid), &lex_index))
cur_g = cur_g->base_graph;

if (cur_g) {
*pos = lex_index + cur_g->num_commits_in_base;
return 1;
}

return 0;
}
}

@@ -492,8 +554,13 @@ static struct tree *load_tree_for_commit(struct repository *r,
struct commit *c)
{
struct object_id oid;
const unsigned char *commit_data = g->chunk_commit_data +
GRAPH_DATA_WIDTH * (c->graph_pos);
const unsigned char *commit_data;

while (c->graph_pos < g->num_commits_in_base)
g = g->base_graph;

commit_data = g->chunk_commit_data +
GRAPH_DATA_WIDTH * (c->graph_pos - g->num_commits_in_base);

hashcpy(oid.hash, commit_data);
c->maybe_tree = lookup_tree(r, &oid);


+ 3
- 0
commit-graph.h View File

@@ -48,6 +48,9 @@ struct commit_graph {
uint32_t num_commits;
struct object_id oid;

uint32_t num_commits_in_base;
struct commit_graph *base_graph;

const uint32_t *chunk_oid_fanout;
const unsigned char *chunk_oid_lookup;
const unsigned char *chunk_commit_data;


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