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git/object.c
Jeff King c868d8e91f parse_object(): allow skipping hash check
The parse_object() function checks the object hash of any object it
parses. This is a nice feature, as it means we may catch bit corruption
during normal use, rather than waiting for specific fsck operations.

But it also can be slow. It's particularly noticeable for blobs, where
except for the hash check, we could return without loading the object
contents at all. Now one may wonder what is the point of calling
parse_object() on a blob in the first place then, but usually it's not
intentional: we were fed an oid from somewhere, don't know the type, and
want an object struct. For commits and trees, the parsing is usually
helpful; we're about to look at the contents anyway. But this is less
true for blobs, where we may be collecting them as part of a
reachability traversal, etc, and don't actually care what's in them. And
blobs, of course, tend to be larger.

We don't want to just throw out the hash-checks for blobs, though. We do
depend on them in some circumstances (e.g., rev-list --verify-objects
uses parse_object() to check them). It's only the callers that know
how they're going to use the result. And so we can help them by
providing a special flag to skip the hash check.

We could just apply this to blobs, as they're going to be the main
source of performance improvement. But if a caller doesn't care about
checking the hash, we might as well skip it for other object types, too.
Even though we can't avoid reading the object contents, we can still
skip the actual hash computation.

If this seems like it is making Git a little bit less safe against
corruption, it may be. But it's part of a series of tradeoffs we're
already making. For instance, "rev-list --objects" does not open the
contents of blobs it prints. And when a commit graph is present, we skip
opening most commits entirely. The important thing will be to use this
flag in cases where it's safe to skip the check. For instance, when
serving a pack for a fetch, we know the client will fully index the
objects and do a connectivity check itself. There's little to be gained
from the server side re-hashing a blob itself. And indeed, most of the
time we don't! The revision machinery won't open up a blob reached by
traversal, but only one requested directly with a "want" line. So
applied properly, this new feature shouldn't make anything less safe in
practice.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-09-07 12:18:57 -07:00

611 lines
14 KiB
C

#include "cache.h"
#include "object.h"
#include "replace-object.h"
#include "object-store.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "tag.h"
#include "alloc.h"
#include "packfile.h"
#include "commit-graph.h"
unsigned int get_max_object_index(void)
{
return the_repository->parsed_objects->obj_hash_size;
}
struct object *get_indexed_object(unsigned int idx)
{
return the_repository->parsed_objects->obj_hash[idx];
}
static const char *object_type_strings[] = {
NULL, /* OBJ_NONE = 0 */
"commit", /* OBJ_COMMIT = 1 */
"tree", /* OBJ_TREE = 2 */
"blob", /* OBJ_BLOB = 3 */
"tag", /* OBJ_TAG = 4 */
};
const char *type_name(unsigned int type)
{
if (type >= ARRAY_SIZE(object_type_strings))
return NULL;
return object_type_strings[type];
}
int type_from_string_gently(const char *str, ssize_t len, int gentle)
{
int i;
if (len < 0)
len = strlen(str);
for (i = 1; i < ARRAY_SIZE(object_type_strings); i++)
if (!strncmp(str, object_type_strings[i], len) &&
object_type_strings[i][len] == '\0')
return i;
if (gentle)
return -1;
die(_("invalid object type \"%s\""), str);
}
/*
* Return a numerical hash value between 0 and n-1 for the object with
* the specified sha1. n must be a power of 2. Please note that the
* return value is *not* consistent across computer architectures.
*/
static unsigned int hash_obj(const struct object_id *oid, unsigned int n)
{
return oidhash(oid) & (n - 1);
}
/*
* Insert obj into the hash table hash, which has length size (which
* must be a power of 2). On collisions, simply overflow to the next
* empty bucket.
*/
static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
{
unsigned int j = hash_obj(&obj->oid, size);
while (hash[j]) {
j++;
if (j >= size)
j = 0;
}
hash[j] = obj;
}
/*
* Look up the record for the given sha1 in the hash map stored in
* obj_hash. Return NULL if it was not found.
*/
struct object *lookup_object(struct repository *r, const struct object_id *oid)
{
unsigned int i, first;
struct object *obj;
if (!r->parsed_objects->obj_hash)
return NULL;
first = i = hash_obj(oid, r->parsed_objects->obj_hash_size);
while ((obj = r->parsed_objects->obj_hash[i]) != NULL) {
if (oideq(oid, &obj->oid))
break;
i++;
if (i == r->parsed_objects->obj_hash_size)
i = 0;
}
if (obj && i != first) {
/*
* Move object to where we started to look for it so
* that we do not need to walk the hash table the next
* time we look for it.
*/
SWAP(r->parsed_objects->obj_hash[i],
r->parsed_objects->obj_hash[first]);
}
return obj;
}
/*
* Increase the size of the hash map stored in obj_hash to the next
* power of 2 (but at least 32). Copy the existing values to the new
* hash map.
*/
static void grow_object_hash(struct repository *r)
{
int i;
/*
* Note that this size must always be power-of-2 to match hash_obj
* above.
*/
int new_hash_size = r->parsed_objects->obj_hash_size < 32 ? 32 : 2 * r->parsed_objects->obj_hash_size;
struct object **new_hash;
CALLOC_ARRAY(new_hash, new_hash_size);
for (i = 0; i < r->parsed_objects->obj_hash_size; i++) {
struct object *obj = r->parsed_objects->obj_hash[i];
if (!obj)
continue;
insert_obj_hash(obj, new_hash, new_hash_size);
}
free(r->parsed_objects->obj_hash);
r->parsed_objects->obj_hash = new_hash;
r->parsed_objects->obj_hash_size = new_hash_size;
}
void *create_object(struct repository *r, const struct object_id *oid, void *o)
{
struct object *obj = o;
obj->parsed = 0;
obj->flags = 0;
oidcpy(&obj->oid, oid);
if (r->parsed_objects->obj_hash_size - 1 <= r->parsed_objects->nr_objs * 2)
grow_object_hash(r);
insert_obj_hash(obj, r->parsed_objects->obj_hash,
r->parsed_objects->obj_hash_size);
r->parsed_objects->nr_objs++;
return obj;
}
void *object_as_type(struct object *obj, enum object_type type, int quiet)
{
if (obj->type == type)
return obj;
else if (obj->type == OBJ_NONE) {
if (type == OBJ_COMMIT)
init_commit_node((struct commit *) obj);
else
obj->type = type;
return obj;
}
else {
if (!quiet)
error(_("object %s is a %s, not a %s"),
oid_to_hex(&obj->oid),
type_name(obj->type), type_name(type));
return NULL;
}
}
struct object *lookup_unknown_object(struct repository *r, const struct object_id *oid)
{
struct object *obj = lookup_object(r, oid);
if (!obj)
obj = create_object(r, oid, alloc_object_node(r));
return obj;
}
struct object *lookup_object_by_type(struct repository *r,
const struct object_id *oid,
enum object_type type)
{
switch (type) {
case OBJ_COMMIT:
return (struct object *)lookup_commit(r, oid);
case OBJ_TREE:
return (struct object *)lookup_tree(r, oid);
case OBJ_TAG:
return (struct object *)lookup_tag(r, oid);
case OBJ_BLOB:
return (struct object *)lookup_blob(r, oid);
default:
BUG("unknown object type %d", type);
}
}
struct object *parse_object_buffer(struct repository *r, const struct object_id *oid, enum object_type type, unsigned long size, void *buffer, int *eaten_p)
{
struct object *obj;
*eaten_p = 0;
obj = NULL;
if (type == OBJ_BLOB) {
struct blob *blob = lookup_blob(r, oid);
if (blob) {
if (parse_blob_buffer(blob, buffer, size))
return NULL;
obj = &blob->object;
}
} else if (type == OBJ_TREE) {
struct tree *tree = lookup_tree(r, oid);
if (tree) {
obj = &tree->object;
if (!tree->buffer)
tree->object.parsed = 0;
if (!tree->object.parsed) {
if (parse_tree_buffer(tree, buffer, size))
return NULL;
*eaten_p = 1;
}
}
} else if (type == OBJ_COMMIT) {
struct commit *commit = lookup_commit(r, oid);
if (commit) {
if (parse_commit_buffer(r, commit, buffer, size, 1))
return NULL;
if (!get_cached_commit_buffer(r, commit, NULL)) {
set_commit_buffer(r, commit, buffer, size);
*eaten_p = 1;
}
obj = &commit->object;
}
} else if (type == OBJ_TAG) {
struct tag *tag = lookup_tag(r, oid);
if (tag) {
if (parse_tag_buffer(r, tag, buffer, size))
return NULL;
obj = &tag->object;
}
} else {
warning(_("object %s has unknown type id %d"), oid_to_hex(oid), type);
obj = NULL;
}
return obj;
}
struct object *parse_object_or_die(const struct object_id *oid,
const char *name)
{
struct object *o = parse_object(the_repository, oid);
if (o)
return o;
die(_("unable to parse object: %s"), name ? name : oid_to_hex(oid));
}
struct object *parse_object_with_flags(struct repository *r,
const struct object_id *oid,
enum parse_object_flags flags)
{
int skip_hash = !!(flags & PARSE_OBJECT_SKIP_HASH_CHECK);
unsigned long size;
enum object_type type;
int eaten;
const struct object_id *repl = lookup_replace_object(r, oid);
void *buffer;
struct object *obj;
obj = lookup_object(r, oid);
if (obj && obj->parsed)
return obj;
if ((obj && obj->type == OBJ_BLOB && repo_has_object_file(r, oid)) ||
(!obj && repo_has_object_file(r, oid) &&
oid_object_info(r, oid, NULL) == OBJ_BLOB)) {
if (!skip_hash && stream_object_signature(r, repl) < 0) {
error(_("hash mismatch %s"), oid_to_hex(oid));
return NULL;
}
parse_blob_buffer(lookup_blob(r, oid), NULL, 0);
return lookup_object(r, oid);
}
buffer = repo_read_object_file(r, oid, &type, &size);
if (buffer) {
if (!skip_hash &&
check_object_signature(r, repl, buffer, size, type) < 0) {
free(buffer);
error(_("hash mismatch %s"), oid_to_hex(repl));
return NULL;
}
obj = parse_object_buffer(r, oid, type, size,
buffer, &eaten);
if (!eaten)
free(buffer);
return obj;
}
return NULL;
}
struct object *parse_object(struct repository *r, const struct object_id *oid)
{
return parse_object_with_flags(r, oid, 0);
}
struct object_list *object_list_insert(struct object *item,
struct object_list **list_p)
{
struct object_list *new_list = xmalloc(sizeof(struct object_list));
new_list->item = item;
new_list->next = *list_p;
*list_p = new_list;
return new_list;
}
int object_list_contains(struct object_list *list, struct object *obj)
{
while (list) {
if (list->item == obj)
return 1;
list = list->next;
}
return 0;
}
void object_list_free(struct object_list **list)
{
while (*list) {
struct object_list *p = *list;
*list = p->next;
free(p);
}
}
/*
* A zero-length string to which object_array_entry::name can be
* initialized without requiring a malloc/free.
*/
static char object_array_slopbuf[1];
void add_object_array_with_path(struct object *obj, const char *name,
struct object_array *array,
unsigned mode, const char *path)
{
unsigned nr = array->nr;
unsigned alloc = array->alloc;
struct object_array_entry *objects = array->objects;
struct object_array_entry *entry;
if (nr >= alloc) {
alloc = (alloc + 32) * 2;
REALLOC_ARRAY(objects, alloc);
array->alloc = alloc;
array->objects = objects;
}
entry = &objects[nr];
entry->item = obj;
if (!name)
entry->name = NULL;
else if (!*name)
/* Use our own empty string instead of allocating one: */
entry->name = object_array_slopbuf;
else
entry->name = xstrdup(name);
entry->mode = mode;
if (path)
entry->path = xstrdup(path);
else
entry->path = NULL;
array->nr = ++nr;
}
void add_object_array(struct object *obj, const char *name, struct object_array *array)
{
add_object_array_with_path(obj, name, array, S_IFINVALID, NULL);
}
/*
* Free all memory associated with an entry; the result is
* in an unspecified state and should not be examined.
*/
static void object_array_release_entry(struct object_array_entry *ent)
{
if (ent->name != object_array_slopbuf)
free(ent->name);
free(ent->path);
}
struct object *object_array_pop(struct object_array *array)
{
struct object *ret;
if (!array->nr)
return NULL;
ret = array->objects[array->nr - 1].item;
object_array_release_entry(&array->objects[array->nr - 1]);
array->nr--;
return ret;
}
void object_array_filter(struct object_array *array,
object_array_each_func_t want, void *cb_data)
{
unsigned nr = array->nr, src, dst;
struct object_array_entry *objects = array->objects;
for (src = dst = 0; src < nr; src++) {
if (want(&objects[src], cb_data)) {
if (src != dst)
objects[dst] = objects[src];
dst++;
} else {
object_array_release_entry(&objects[src]);
}
}
array->nr = dst;
}
void object_array_clear(struct object_array *array)
{
int i;
for (i = 0; i < array->nr; i++)
object_array_release_entry(&array->objects[i]);
FREE_AND_NULL(array->objects);
array->nr = array->alloc = 0;
}
/*
* Return true if array already contains an entry.
*/
static int contains_object(struct object_array *array,
const struct object *item, const char *name)
{
unsigned nr = array->nr, i;
struct object_array_entry *object = array->objects;
for (i = 0; i < nr; i++, object++)
if (item == object->item && !strcmp(object->name, name))
return 1;
return 0;
}
void object_array_remove_duplicates(struct object_array *array)
{
unsigned nr = array->nr, src;
struct object_array_entry *objects = array->objects;
array->nr = 0;
for (src = 0; src < nr; src++) {
if (!contains_object(array, objects[src].item,
objects[src].name)) {
if (src != array->nr)
objects[array->nr] = objects[src];
array->nr++;
} else {
object_array_release_entry(&objects[src]);
}
}
}
void clear_object_flags(unsigned flags)
{
int i;
for (i=0; i < the_repository->parsed_objects->obj_hash_size; i++) {
struct object *obj = the_repository->parsed_objects->obj_hash[i];
if (obj)
obj->flags &= ~flags;
}
}
void repo_clear_commit_marks(struct repository *r, unsigned int flags)
{
int i;
for (i = 0; i < r->parsed_objects->obj_hash_size; i++) {
struct object *obj = r->parsed_objects->obj_hash[i];
if (obj && obj->type == OBJ_COMMIT)
obj->flags &= ~flags;
}
}
struct parsed_object_pool *parsed_object_pool_new(void)
{
struct parsed_object_pool *o = xmalloc(sizeof(*o));
memset(o, 0, sizeof(*o));
o->blob_state = allocate_alloc_state();
o->tree_state = allocate_alloc_state();
o->commit_state = allocate_alloc_state();
o->tag_state = allocate_alloc_state();
o->object_state = allocate_alloc_state();
o->is_shallow = -1;
CALLOC_ARRAY(o->shallow_stat, 1);
o->buffer_slab = allocate_commit_buffer_slab();
return o;
}
struct raw_object_store *raw_object_store_new(void)
{
struct raw_object_store *o = xmalloc(sizeof(*o));
memset(o, 0, sizeof(*o));
INIT_LIST_HEAD(&o->packed_git_mru);
hashmap_init(&o->pack_map, pack_map_entry_cmp, NULL, 0);
pthread_mutex_init(&o->replace_mutex, NULL);
return o;
}
void free_object_directory(struct object_directory *odb)
{
free(odb->path);
odb_clear_loose_cache(odb);
free(odb);
}
static void free_object_directories(struct raw_object_store *o)
{
while (o->odb) {
struct object_directory *next;
next = o->odb->next;
free_object_directory(o->odb);
o->odb = next;
}
kh_destroy_odb_path_map(o->odb_by_path);
o->odb_by_path = NULL;
}
void raw_object_store_clear(struct raw_object_store *o)
{
FREE_AND_NULL(o->alternate_db);
oidmap_free(o->replace_map, 1);
FREE_AND_NULL(o->replace_map);
pthread_mutex_destroy(&o->replace_mutex);
free_commit_graph(o->commit_graph);
o->commit_graph = NULL;
o->commit_graph_attempted = 0;
free_object_directories(o);
o->odb_tail = NULL;
o->loaded_alternates = 0;
INIT_LIST_HEAD(&o->packed_git_mru);
close_object_store(o);
o->packed_git = NULL;
hashmap_clear(&o->pack_map);
}
void parsed_object_pool_clear(struct parsed_object_pool *o)
{
/*
* As objects are allocated in slabs (see alloc.c), we do
* not need to free each object, but each slab instead.
*
* Before doing so, we need to free any additional memory
* the objects may hold.
*/
unsigned i;
for (i = 0; i < o->obj_hash_size; i++) {
struct object *obj = o->obj_hash[i];
if (!obj)
continue;
if (obj->type == OBJ_TREE)
free_tree_buffer((struct tree*)obj);
else if (obj->type == OBJ_COMMIT)
release_commit_memory(o, (struct commit*)obj);
else if (obj->type == OBJ_TAG)
release_tag_memory((struct tag*)obj);
}
FREE_AND_NULL(o->obj_hash);
o->obj_hash_size = 0;
free_commit_buffer_slab(o->buffer_slab);
o->buffer_slab = NULL;
clear_alloc_state(o->blob_state);
clear_alloc_state(o->tree_state);
clear_alloc_state(o->commit_state);
clear_alloc_state(o->tag_state);
clear_alloc_state(o->object_state);
stat_validity_clear(o->shallow_stat);
FREE_AND_NULL(o->blob_state);
FREE_AND_NULL(o->tree_state);
FREE_AND_NULL(o->commit_state);
FREE_AND_NULL(o->tag_state);
FREE_AND_NULL(o->object_state);
FREE_AND_NULL(o->shallow_stat);
}