c868d8e91f
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>
223 lines
7.3 KiB
C
223 lines
7.3 KiB
C
#ifndef OBJECT_H
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#define OBJECT_H
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#include "cache.h"
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struct buffer_slab;
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struct parsed_object_pool {
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struct object **obj_hash;
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int nr_objs, obj_hash_size;
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/* TODO: migrate alloc_states to mem-pool? */
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struct alloc_state *blob_state;
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struct alloc_state *tree_state;
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struct alloc_state *commit_state;
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struct alloc_state *tag_state;
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struct alloc_state *object_state;
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/* parent substitutions from .git/info/grafts and .git/shallow */
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struct commit_graft **grafts;
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int grafts_alloc, grafts_nr;
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int is_shallow;
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struct stat_validity *shallow_stat;
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char *alternate_shallow_file;
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int commit_graft_prepared;
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int substituted_parent;
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struct buffer_slab *buffer_slab;
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};
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struct parsed_object_pool *parsed_object_pool_new(void);
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void parsed_object_pool_clear(struct parsed_object_pool *o);
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struct object_list {
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struct object *item;
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struct object_list *next;
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};
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struct object_array {
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unsigned int nr;
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unsigned int alloc;
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struct object_array_entry {
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struct object *item;
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/*
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* name or NULL. If non-NULL, the memory pointed to
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* is owned by this object *except* if it points at
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* object_array_slopbuf, which is a static copy of the
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* empty string.
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*/
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char *name;
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char *path;
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unsigned mode;
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} *objects;
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};
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#define OBJECT_ARRAY_INIT { 0 }
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/*
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* object flag allocation:
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* revision.h: 0---------10 15 23------27
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* fetch-pack.c: 01 67
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* negotiator/default.c: 2--5
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* walker.c: 0-2
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* upload-pack.c: 4 11-----14 16-----19
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* builtin/blame.c: 12-13
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* bisect.c: 16
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* bundle.c: 16
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* http-push.c: 11-----14
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* commit-graph.c: 15
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* commit-reach.c: 16-----19
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* sha1-name.c: 20
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* list-objects-filter.c: 21
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* builtin/fsck.c: 0--3
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* builtin/gc.c: 0
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* builtin/index-pack.c: 2021
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* reflog.c: 10--12
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* builtin/show-branch.c: 0-------------------------------------------26
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* builtin/unpack-objects.c: 2021
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*/
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#define FLAG_BITS 28
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/*
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* The object type is stored in 3 bits.
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*/
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struct object {
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unsigned parsed : 1;
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unsigned type : TYPE_BITS;
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unsigned flags : FLAG_BITS;
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struct object_id oid;
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};
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const char *type_name(unsigned int type);
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int type_from_string_gently(const char *str, ssize_t, int gentle);
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#define type_from_string(str) type_from_string_gently(str, -1, 0)
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/*
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* Return the current number of buckets in the object hashmap.
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*/
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unsigned int get_max_object_index(void);
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/*
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* Return the object from the specified bucket in the object hashmap.
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*/
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struct object *get_indexed_object(unsigned int);
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/*
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* This can be used to see if we have heard of the object before, but
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* it can return "yes we have, and here is a half-initialised object"
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* for an object that we haven't loaded/parsed yet.
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*
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* When parsing a commit to create an in-core commit object, its
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* parents list holds commit objects that represent its parents, but
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* they are expected to be lazily initialized and do not know what
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* their trees or parents are yet. When this function returns such a
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* half-initialised objects, the caller is expected to initialize them
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* by calling parse_object() on them.
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*/
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struct object *lookup_object(struct repository *r, const struct object_id *oid);
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void *create_object(struct repository *r, const struct object_id *oid, void *obj);
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void *object_as_type(struct object *obj, enum object_type type, int quiet);
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/*
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* Returns the object, having parsed it to find out what it is.
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*
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* Returns NULL if the object is missing or corrupt.
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*/
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enum parse_object_flags {
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PARSE_OBJECT_SKIP_HASH_CHECK = 1 << 0,
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};
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struct object *parse_object(struct repository *r, const struct object_id *oid);
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struct object *parse_object_with_flags(struct repository *r,
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const struct object_id *oid,
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enum parse_object_flags flags);
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/*
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* Like parse_object, but will die() instead of returning NULL. If the
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* "name" parameter is not NULL, it is included in the error message
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* (otherwise, the hex object ID is given).
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*/
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struct object *parse_object_or_die(const struct object_id *oid, const char *name);
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/* Given the result of read_sha1_file(), returns the object after
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* parsing it. eaten_p indicates if the object has a borrowed copy
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* of buffer and the caller should not free() it.
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*/
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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);
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/*
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* Allocate and return an object struct, even if you do not know the type of
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* the object. The returned object may have its "type" field set to a real type
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* (if somebody previously called lookup_blob(), etc), or it may be set to
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* OBJ_NONE. In the latter case, subsequent calls to lookup_blob(), etc, will
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* set the type field as appropriate.
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*
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* Use this when you do not know the expected type of an object and want to
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* avoid parsing it for efficiency reasons. Try to avoid it otherwise; it
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* may allocate excess memory, since the returned object must be as large as
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* the maximum struct of any type.
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*/
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struct object *lookup_unknown_object(struct repository *r, const struct object_id *oid);
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/*
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* Dispatch to the appropriate lookup_blob(), lookup_commit(), etc, based on
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* "type".
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*/
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struct object *lookup_object_by_type(struct repository *r, const struct object_id *oid,
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enum object_type type);
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struct object_list *object_list_insert(struct object *item,
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struct object_list **list_p);
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int object_list_contains(struct object_list *list, struct object *obj);
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void object_list_free(struct object_list **list);
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/* Object array handling .. */
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void add_object_array(struct object *obj, const char *name, struct object_array *array);
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void add_object_array_with_path(struct object *obj, const char *name, struct object_array *array, unsigned mode, const char *path);
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/*
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* Returns NULL if the array is empty. Otherwise, returns the last object
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* after removing its entry from the array. Other resources associated
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* with that object are left in an unspecified state and should not be
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* examined.
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*/
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struct object *object_array_pop(struct object_array *array);
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typedef int (*object_array_each_func_t)(struct object_array_entry *, void *);
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/*
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* Apply want to each entry in array, retaining only the entries for
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* which the function returns true. Preserve the order of the entries
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* that are retained.
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*/
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void object_array_filter(struct object_array *array,
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object_array_each_func_t want, void *cb_data);
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/*
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* Remove from array all but the first entry with a given name.
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* Warning: this function uses an O(N^2) algorithm.
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*/
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void object_array_remove_duplicates(struct object_array *array);
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/*
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* Remove any objects from the array, freeing all used memory; afterwards
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* the array is ready to store more objects with add_object_array().
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*/
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void object_array_clear(struct object_array *array);
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void clear_object_flags(unsigned flags);
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/*
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* Clear the specified object flags from all in-core commit objects from
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* the specified repository.
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*/
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void repo_clear_commit_marks(struct repository *r, unsigned int flags);
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#endif /* OBJECT_H */
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