Files
git/repo-settings.c
Michael Montalbo 42824db113 diff-hunks: add the store format, library, and command
Blame and "git log --stat" recover hunk coordinates by diffing blob
pairs, and recompute them on every run.  Add a cache of those
coordinates at $GIT_DIR/objects/info/diff-hunks, beside the
commit-graph, so a later run can look them up instead of decompressing
the blobs and running xdiff again.

The store is a single chunk-format file (see gitformat-chunk(5)): an
8-byte header, a DHIX index of fixed-size entries sorted by key, a DHDT
segment of hunk records, and a trailing hash checksum.  An entry is
keyed by the two blob object ids and the xdl_opts the pair was diffed
under, so a stored result is served only where that exact key recurs,
independent of path.  A zero-context diff trims unchanged lines from
hunk edges and can pick a different but equally valid set of hunks than
an untrimmed diff, so a recording caller stores a pair only when its
trimmed and untrimmed diffs are identical; such an entry answers any
consumer at any context, and the rare divergent pair is always
computed.  Identical hunk blocks are interned once and shared across
keys.

The library provides a reader (repo_diff_hunks_store and _replay, gated
by core.diffHunks), loaded once and cached on the object database as the
commit-graph is, and a writer that accumulates entries and flushes them
in one atomic pass.  An absent, corrupt, or disabled store reads as all
misses.  A record with no hunks is invalid too: replaying it would claim
the pair equivalent, which the store never asserts, so it reads as a
miss.

Ordinary reads are diagnostic-free.  Loading parses the chunk table
through read_table_of_contents_quiet(), new in chunk-format, which
prints nothing on a malformed table and takes the repository's hash
algorithm rather than the_hash_algo, so the file is bounds-checked under
the algorithm it is keyed by.

The flush closes the repository's mmapped store and forgets that loading
was attempted before committing the lockfile.  A warming run that also
reads may hold the file it is replacing mapped, and the rename must not
land on a live mapping, which Windows refuses; a read after the flush
then observes the committed file.  commit-graph closes its graph before
committing for the same reason.

Writing is off by default, enabled per run by GIT_DIFF_HUNKS_WRITE or
persistently by diffHunks.write, the environment winning.  A writer
seeds from the existing store, so a flush merges rather than replaces.
The seed's checksum is verified first: a corrupt store is discarded, not
rewritten with a fresh checksum verify could no longer catch.  An entry
that fails the shared diff_provider_check_hunk() or names no blob is
dropped with a warning, since it would only ever read as a miss.  A seed
that discarded or dropped anything forces the flush even when the
warming run computed nothing new.  The writer fsyncs through a new
diff-hunks core.fsync component.

"git diff-hunks" inspects and manages the file: "verify" checks the
checksum, chunk table, sort order, entry bounds, and every entry's hunk
sequence against that shared check, so a store whose entries could only
read as misses fails verify; "clear" removes the file.  Later patches
wire the readers and the writer into the diff and blame paths.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2026-08-01 15:09:51 -07:00

221 lines
7.2 KiB
C

#include "git-compat-util.h"
#include "config.h"
#include "repo-settings.h"
#include "repository.h"
#include "midx.h"
#include "pack-objects.h"
#include "setup.h"
static void repo_cfg_bool(struct repository *r, const char *key, int *dest,
int def)
{
if (repo_config_get_bool(r, key, dest))
*dest = def;
}
static void repo_cfg_int(struct repository *r, const char *key, int *dest,
int def)
{
if (repo_config_get_int(r, key, dest))
*dest = def;
}
static void repo_cfg_ulong(struct repository *r, const char *key, unsigned long *dest,
unsigned long def)
{
if (repo_config_get_ulong(r, key, dest))
*dest = def;
}
void prepare_repo_settings(struct repository *r)
{
int experimental;
int value;
const char *strval;
int manyfiles;
int read_changed_paths;
unsigned long ulongval;
if (!r->gitdir)
BUG("Cannot add settings for uninitialized repository");
if (r->settings.initialized)
return;
repo_settings_clear(r);
r->settings.initialized++;
/* Booleans config or default, cascades to other settings */
repo_cfg_bool(r, "feature.manyfiles", &manyfiles, 0);
repo_cfg_bool(r, "feature.experimental", &experimental, 0);
/* Defaults modified by feature.* */
if (experimental) {
r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
r->settings.pack_use_bitmap_boundary_traversal = 1;
r->settings.pack_use_multi_pack_reuse = 1;
r->settings.pack_use_path_walk = 1;
}
if (manyfiles) {
r->settings.index_version = 4;
r->settings.index_skip_hash = 1;
r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
r->settings.pack_use_path_walk = 1;
}
/* Commit graph config or default, does not cascade (simple) */
repo_cfg_bool(r, "core.commitgraph", &r->settings.core_commit_graph, 1);
repo_cfg_int(r, "commitgraph.generationversion", &r->settings.commit_graph_generation_version, 2);
repo_cfg_bool(r, "commitgraph.readchangedpaths", &read_changed_paths, 1);
repo_cfg_int(r, "commitgraph.changedpathsversion",
&r->settings.commit_graph_changed_paths_version,
read_changed_paths ? -1 : 0);
repo_cfg_bool(r, "gc.writecommitgraph", &r->settings.gc_write_commit_graph, 1);
repo_cfg_bool(r, "fetch.writecommitgraph", &r->settings.fetch_write_commit_graph, 0);
/* Boolean config or default, does not cascade (simple) */
repo_cfg_bool(r, "pack.usesparse", &r->settings.pack_use_sparse, 1);
repo_cfg_bool(r, "pack.usepathwalk", &r->settings.pack_use_path_walk, 0);
repo_cfg_bool(r, "core.multipackindex", &r->settings.core_multi_pack_index, 1);
repo_cfg_bool(r, "core.diffhunks", &r->settings.core_diff_hunks, 1);
repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 0);
repo_cfg_bool(r, "index.skiphash", &r->settings.index_skip_hash, r->settings.index_skip_hash);
repo_cfg_bool(r, "pack.readreverseindex", &r->settings.pack_read_reverse_index, 1);
repo_cfg_bool(r, "pack.usebitmapboundarytraversal",
&r->settings.pack_use_bitmap_boundary_traversal,
r->settings.pack_use_bitmap_boundary_traversal);
repo_cfg_bool(r, "core.usereplacerefs", &r->settings.read_replace_refs, 1);
/*
* The GIT_TEST_MULTI_PACK_INDEX variable is special in that
* either it *or* the config sets
* r->settings.core_multi_pack_index if true. We don't take
* the environment variable if it exists (even if false) over
* any config, as in most other cases.
*/
if (git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0))
r->settings.core_multi_pack_index = 1;
/*
* Non-boolean config
*/
if (!repo_config_get_int(r, "index.version", &value))
r->settings.index_version = value;
repo_cfg_int(r, "core.maxtreedepth",
&r->settings.max_allowed_tree_depth,
DEFAULT_MAX_ALLOWED_TREE_DEPTH);
if (!repo_config_get_string_tmp(r, "core.untrackedcache", &strval)) {
int v = git_parse_maybe_bool(strval);
/*
* If it's set to "keep", or some other non-boolean
* value then "v < 0". Then we do nothing and keep it
* at the default of UNTRACKED_CACHE_KEEP.
*/
if (v >= 0)
r->settings.core_untracked_cache = v ?
UNTRACKED_CACHE_WRITE : UNTRACKED_CACHE_REMOVE;
}
if (!repo_config_get_string_tmp(r, "fetch.negotiationalgorithm", &strval)) {
int fetch_default = r->settings.fetch_negotiation_algorithm;
if (!strcasecmp(strval, "skipping"))
r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
else if (!strcasecmp(strval, "noop"))
r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_NOOP;
else if (!strcasecmp(strval, "consecutive"))
r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_CONSECUTIVE;
else if (!strcasecmp(strval, "default"))
r->settings.fetch_negotiation_algorithm = fetch_default;
else
die("unknown fetch negotiation algorithm '%s'", strval);
}
/*
* This setting guards all index reads to require a full index
* over a sparse index. After suitable guards are placed in the
* codebase around uses of the index, this setting will be
* removed.
*/
r->settings.command_requires_full_index = 1;
if (!repo_config_get_ulong(r, "core.deltabasecachelimit", &ulongval))
r->settings.delta_base_cache_limit = ulongval;
if (!repo_config_get_ulong(r, "core.packedgitwindowsize", &ulongval)) {
int pgsz_x2 = getpagesize() * 2;
/* This value must be multiple of (pagesize * 2) */
ulongval /= pgsz_x2;
if (ulongval < 1)
ulongval = 1;
r->settings.packed_git_window_size = ulongval * pgsz_x2;
}
if (!repo_config_get_ulong(r, "core.packedgitlimit", &ulongval))
r->settings.packed_git_limit = ulongval;
}
void repo_settings_clear(struct repository *r)
{
struct repo_settings empty = REPO_SETTINGS_INIT;
FREE_AND_NULL(r->settings.fsmonitor);
FREE_AND_NULL(r->settings.hooks_path);
r->settings = empty;
}
unsigned long repo_settings_get_big_file_threshold(struct repository *repo)
{
if (!repo->settings.big_file_threshold)
repo_cfg_ulong(repo, "core.bigfilethreshold",
&repo->settings.big_file_threshold, 512 * 1024 * 1024);
return repo->settings.big_file_threshold;
}
void repo_settings_set_big_file_threshold(struct repository *repo, unsigned long value)
{
repo->settings.big_file_threshold = value;
}
int repo_settings_get_warn_ambiguous_refs(struct repository *repo)
{
prepare_repo_settings(repo);
if (repo->settings.warn_ambiguous_refs < 0)
repo_cfg_bool(repo, "core.warnambiguousrefs",
&repo->settings.warn_ambiguous_refs, 1);
return repo->settings.warn_ambiguous_refs;
}
const char *repo_settings_get_hooks_path(struct repository *repo)
{
if (!repo->settings.hooks_path)
repo_config_get_pathname(repo, "core.hookspath", &repo->settings.hooks_path);
return repo->settings.hooks_path;
}
int repo_settings_get_shared_repository(struct repository *repo)
{
if (!repo->settings.shared_repository_initialized) {
const char *var = "core.sharedrepository";
const char *value;
if (!repo_config_get_value(repo, var, &value))
repo->settings.shared_repository = git_config_perm(var, value);
else
repo->settings.shared_repository = PERM_UMASK;
repo->settings.shared_repository_initialized = 1;
}
return repo->settings.shared_repository;
}
void repo_settings_set_shared_repository(struct repository *repo, int value)
{
repo->settings.shared_repository = value;
repo->settings.shared_repository_initialized = 1;
}
void repo_settings_reset_shared_repository(struct repository *repo)
{
repo->settings.shared_repository_initialized = 0;
}