1 #ifndef REFS_REFS_INTERNAL_H
2 #define REFS_REFS_INTERNAL_H
3 
4 #include "cache.h"
5 #include "refs.h"
6 #include "iterator.h"
7 
8 struct ref_transaction;
9 
10 /*
11  * Data structures and functions for the internal use of the refs
12  * module. Code outside of the refs module should use only the public
13  * functions defined in "refs.h", and should *not* include this file.
14  */
15 
16 /*
17  * The following flags can appear in `ref_update::flags`. Their
18  * numerical values must not conflict with those of REF_NO_DEREF and
19  * REF_FORCE_CREATE_REFLOG, which are also stored in
20  * `ref_update::flags`.
21  */
22 
23 /*
24  * The reference should be updated to new_oid.
25  */
26 #define REF_HAVE_NEW (1 << 2)
27 
28 /*
29  * The current reference's value should be checked to make sure that
30  * it agrees with old_oid.
31  */
32 #define REF_HAVE_OLD (1 << 3)
33 
34 /*
35  * Used as a flag in ref_update::flags when we want to log a ref
36  * update but not actually perform it.  This is used when a symbolic
37  * ref update is split up.
38  */
39 #define REF_LOG_ONLY (1 << 7)
40 
41 /*
42  * Return the length of time to retry acquiring a loose reference lock
43  * before giving up, in milliseconds:
44  */
45 long get_files_ref_lock_timeout_ms(void);
46 
47 /*
48  * Return true iff refname is minimally safe. "Safe" here means that
49  * deleting a loose reference by this name will not do any damage, for
50  * example by causing a file that is not a reference to be deleted.
51  * This function does not check that the reference name is legal; for
52  * that, use check_refname_format().
53  *
54  * A refname that starts with "refs/" is considered safe iff it
55  * doesn't contain any "." or ".." components or consecutive '/'
56  * characters, end with '/', or (on Windows) contain any '\'
57  * characters. Names that do not start with "refs/" are considered
58  * safe iff they consist entirely of upper case characters and '_'
59  * (like "HEAD" and "MERGE_HEAD" but not "config" or "FOO/BAR").
60  */
61 int refname_is_safe(const char *refname);
62 
63 /*
64  * Helper function: return true if refname, which has the specified
65  * oid and flags, can be resolved to an object in the database. If the
66  * referred-to object does not exist, emit a warning and return false.
67  */
68 int ref_resolves_to_object(const char *refname,
69 			   struct repository *repo,
70 			   const struct object_id *oid,
71 			   unsigned int flags);
72 
73 enum peel_status {
74 	/* object was peeled successfully: */
75 	PEEL_PEELED = 0,
76 
77 	/*
78 	 * object cannot be peeled because the named object (or an
79 	 * object referred to by a tag in the peel chain), does not
80 	 * exist.
81 	 */
82 	PEEL_INVALID = -1,
83 
84 	/* object cannot be peeled because it is not a tag: */
85 	PEEL_NON_TAG = -2,
86 
87 	/* ref_entry contains no peeled value because it is a symref: */
88 	PEEL_IS_SYMREF = -3,
89 
90 	/*
91 	 * ref_entry cannot be peeled because it is broken (i.e., the
92 	 * symbolic reference cannot even be resolved to an object
93 	 * name):
94 	 */
95 	PEEL_BROKEN = -4
96 };
97 
98 /*
99  * Peel the named object; i.e., if the object is a tag, resolve the
100  * tag recursively until a non-tag is found.  If successful, store the
101  * result to oid and return PEEL_PEELED.  If the object is not a tag
102  * or is not valid, return PEEL_NON_TAG or PEEL_INVALID, respectively,
103  * and leave oid unchanged.
104  */
105 enum peel_status peel_object(const struct object_id *name, struct object_id *oid);
106 
107 /**
108  * Information needed for a single ref update. Set new_oid to the new
109  * value or to null_oid to delete the ref. To check the old value
110  * while the ref is locked, set (flags & REF_HAVE_OLD) and set old_oid
111  * to the old value, or to null_oid to ensure the ref does not exist
112  * before update.
113  */
114 struct ref_update {
115 	/*
116 	 * If (flags & REF_HAVE_NEW), set the reference to this value
117 	 * (or delete it, if `new_oid` is `null_oid`).
118 	 */
119 	struct object_id new_oid;
120 
121 	/*
122 	 * If (flags & REF_HAVE_OLD), check that the reference
123 	 * previously had this value (or didn't previously exist, if
124 	 * `old_oid` is `null_oid`).
125 	 */
126 	struct object_id old_oid;
127 
128 	/*
129 	 * One or more of REF_NO_DEREF, REF_FORCE_CREATE_REFLOG,
130 	 * REF_HAVE_NEW, REF_HAVE_OLD, or backend-specific flags.
131 	 */
132 	unsigned int flags;
133 
134 	void *backend_data;
135 	unsigned int type;
136 	char *msg;
137 
138 	/*
139 	 * If this ref_update was split off of a symref update via
140 	 * split_symref_update(), then this member points at that
141 	 * update. This is used for two purposes:
142 	 * 1. When reporting errors, we report the refname under which
143 	 *    the update was originally requested.
144 	 * 2. When we read the old value of this reference, we
145 	 *    propagate it back to its parent update for recording in
146 	 *    the latter's reflog.
147 	 */
148 	struct ref_update *parent_update;
149 
150 	const char refname[FLEX_ARRAY];
151 };
152 
153 int refs_read_raw_ref(struct ref_store *ref_store,
154 		      const char *refname, struct object_id *oid,
155 		      struct strbuf *referent, unsigned int *type);
156 
157 /*
158  * Write an error to `err` and return a nonzero value iff the same
159  * refname appears multiple times in `refnames`. `refnames` must be
160  * sorted on entry to this function.
161  */
162 int ref_update_reject_duplicates(struct string_list *refnames,
163 				 struct strbuf *err);
164 
165 /*
166  * Add a ref_update with the specified properties to transaction, and
167  * return a pointer to the new object. This function does not verify
168  * that refname is well-formed. new_oid and old_oid are only
169  * dereferenced if the REF_HAVE_NEW and REF_HAVE_OLD bits,
170  * respectively, are set in flags.
171  */
172 struct ref_update *ref_transaction_add_update(
173 		struct ref_transaction *transaction,
174 		const char *refname, unsigned int flags,
175 		const struct object_id *new_oid,
176 		const struct object_id *old_oid,
177 		const char *msg);
178 
179 /*
180  * Transaction states.
181  *
182  * OPEN:   The transaction is initialized and new updates can still be
183  *         added to it. An OPEN transaction can be prepared,
184  *         committed, freed, or aborted (freeing and aborting an open
185  *         transaction are equivalent).
186  *
187  * PREPARED: ref_transaction_prepare(), which locks all of the
188  *         references involved in the update and checks that the
189  *         update has no errors, has been called successfully for the
190  *         transaction. A PREPARED transaction can be committed or
191  *         aborted.
192  *
193  * CLOSED: The transaction is no longer active. A transaction becomes
194  *         CLOSED if there is a failure while building the transaction
195  *         or if a transaction is committed or aborted. A CLOSED
196  *         transaction can only be freed.
197  */
198 enum ref_transaction_state {
199 	REF_TRANSACTION_OPEN     = 0,
200 	REF_TRANSACTION_PREPARED = 1,
201 	REF_TRANSACTION_CLOSED   = 2
202 };
203 
204 /*
205  * Data structure for holding a reference transaction, which can
206  * consist of checks and updates to multiple references, carried out
207  * as atomically as possible.  This structure is opaque to callers.
208  */
209 struct ref_transaction {
210 	struct ref_store *ref_store;
211 	struct ref_update **updates;
212 	size_t alloc;
213 	size_t nr;
214 	enum ref_transaction_state state;
215 	void *backend_data;
216 };
217 
218 /*
219  * Check for entries in extras that are within the specified
220  * directory, where dirname is a reference directory name including
221  * the trailing slash (e.g., "refs/heads/foo/"). Ignore any
222  * conflicting references that are found in skip. If there is a
223  * conflicting reference, return its name.
224  *
225  * extras and skip must be sorted lists of reference names. Either one
226  * can be NULL, signifying the empty list.
227  */
228 const char *find_descendant_ref(const char *dirname,
229 				const struct string_list *extras,
230 				const struct string_list *skip);
231 
232 /*
233  * Check whether an attempt to rename old_refname to new_refname would
234  * cause a D/F conflict with any existing reference (other than
235  * possibly old_refname). If there would be a conflict, emit an error
236  * message and return false; otherwise, return true.
237  *
238  * Note that this function is not safe against all races with other
239  * processes (though rename_ref() catches some races that might get by
240  * this check).
241  */
242 int refs_rename_ref_available(struct ref_store *refs,
243 			      const char *old_refname,
244 			      const char *new_refname);
245 
246 /* We allow "recursive" symbolic refs. Only within reason, though */
247 #define SYMREF_MAXDEPTH 5
248 
249 /*
250  * These flags are passed to refs_ref_iterator_begin() (and do_for_each_ref(),
251  * which feeds it).
252  */
253 enum do_for_each_ref_flags {
254 	/*
255 	 * Include broken references in a do_for_each_ref*() iteration, which
256 	 * would normally be omitted. This includes both refs that point to
257 	 * missing objects (a true repository corruption), ones with illegal
258 	 * names (which we prefer not to expose to callers), as well as
259 	 * dangling symbolic refs (i.e., those that point to a non-existent
260 	 * ref; this is not a corruption, but as they have no valid oid, we
261 	 * omit them from normal iteration results).
262 	 */
263 	DO_FOR_EACH_INCLUDE_BROKEN = (1 << 0),
264 
265 	/*
266 	 * Only include per-worktree refs in a do_for_each_ref*() iteration.
267 	 * Normally this will be used with a files ref_store, since that's
268 	 * where all reference backends will presumably store their
269 	 * per-worktree refs.
270 	 */
271 	DO_FOR_EACH_PER_WORKTREE_ONLY = (1 << 1),
272 
273 	/*
274 	 * Omit dangling symrefs from output; this only has an effect with
275 	 * INCLUDE_BROKEN, since they are otherwise not included at all.
276 	 */
277 	DO_FOR_EACH_OMIT_DANGLING_SYMREFS = (1 << 2),
278 };
279 
280 /*
281  * Reference iterators
282  *
283  * A reference iterator encapsulates the state of an in-progress
284  * iteration over references. Create an instance of `struct
285  * ref_iterator` via one of the functions in this module.
286  *
287  * A freshly-created ref_iterator doesn't yet point at a reference. To
288  * advance the iterator, call ref_iterator_advance(). If successful,
289  * this sets the iterator's refname, oid, and flags fields to describe
290  * the next reference and returns ITER_OK. The data pointed at by
291  * refname and oid belong to the iterator; if you want to retain them
292  * after calling ref_iterator_advance() again or calling
293  * ref_iterator_abort(), you must make a copy. When the iteration has
294  * been exhausted, ref_iterator_advance() releases any resources
295  * associated with the iteration, frees the ref_iterator object, and
296  * returns ITER_DONE. If you want to abort the iteration early, call
297  * ref_iterator_abort(), which also frees the ref_iterator object and
298  * any associated resources. If there was an internal error advancing
299  * to the next entry, ref_iterator_advance() aborts the iteration,
300  * frees the ref_iterator, and returns ITER_ERROR.
301  *
302  * The reference currently being looked at can be peeled by calling
303  * ref_iterator_peel(). This function is often faster than peel_ref(),
304  * so it should be preferred when iterating over references.
305  *
306  * Putting it all together, a typical iteration looks like this:
307  *
308  *     int ok;
309  *     struct ref_iterator *iter = ...;
310  *
311  *     while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
312  *             if (want_to_stop_iteration()) {
313  *                     ok = ref_iterator_abort(iter);
314  *                     break;
315  *             }
316  *
317  *             // Access information about the current reference:
318  *             if (!(iter->flags & REF_ISSYMREF))
319  *                     printf("%s is %s\n", iter->refname, oid_to_hex(iter->oid));
320  *
321  *             // If you need to peel the reference:
322  *             ref_iterator_peel(iter, &oid);
323  *     }
324  *
325  *     if (ok != ITER_DONE)
326  *             handle_error();
327  */
328 struct ref_iterator {
329 	struct ref_iterator_vtable *vtable;
330 
331 	/*
332 	 * Does this `ref_iterator` iterate over references in order
333 	 * by refname?
334 	 */
335 	unsigned int ordered : 1;
336 
337 	const char *refname;
338 	const struct object_id *oid;
339 	unsigned int flags;
340 };
341 
342 /*
343  * Advance the iterator to the first or next item and return ITER_OK.
344  * If the iteration is exhausted, free the resources associated with
345  * the ref_iterator and return ITER_DONE. On errors, free the iterator
346  * resources and return ITER_ERROR. It is a bug to use ref_iterator or
347  * call this function again after it has returned ITER_DONE or
348  * ITER_ERROR.
349  */
350 int ref_iterator_advance(struct ref_iterator *ref_iterator);
351 
352 /*
353  * If possible, peel the reference currently being viewed by the
354  * iterator. Return 0 on success.
355  */
356 int ref_iterator_peel(struct ref_iterator *ref_iterator,
357 		      struct object_id *peeled);
358 
359 /*
360  * End the iteration before it has been exhausted, freeing the
361  * reference iterator and any associated resources and returning
362  * ITER_DONE. If the abort itself failed, return ITER_ERROR.
363  */
364 int ref_iterator_abort(struct ref_iterator *ref_iterator);
365 
366 /*
367  * An iterator over nothing (its first ref_iterator_advance() call
368  * returns ITER_DONE).
369  */
370 struct ref_iterator *empty_ref_iterator_begin(void);
371 
372 /*
373  * Return true iff ref_iterator is an empty_ref_iterator.
374  */
375 int is_empty_ref_iterator(struct ref_iterator *ref_iterator);
376 
377 /*
378  * Return an iterator that goes over each reference in `refs` for
379  * which the refname begins with prefix. If trim is non-zero, then
380  * trim that many characters off the beginning of each refname.
381  * The output is ordered by refname.
382  */
383 struct ref_iterator *refs_ref_iterator_begin(
384 		struct ref_store *refs,
385 		const char *prefix, int trim,
386 		enum do_for_each_ref_flags flags);
387 
388 /*
389  * A callback function used to instruct merge_ref_iterator how to
390  * interleave the entries from iter0 and iter1. The function should
391  * return one of the constants defined in enum iterator_selection. It
392  * must not advance either of the iterators itself.
393  *
394  * The function must be prepared to handle the case that iter0 and/or
395  * iter1 is NULL, which indicates that the corresponding sub-iterator
396  * has been exhausted. Its return value must be consistent with the
397  * current states of the iterators; e.g., it must not return
398  * ITER_SKIP_1 if iter1 has already been exhausted.
399  */
400 typedef enum iterator_selection ref_iterator_select_fn(
401 		struct ref_iterator *iter0, struct ref_iterator *iter1,
402 		void *cb_data);
403 
404 /*
405  * Iterate over the entries from iter0 and iter1, with the values
406  * interleaved as directed by the select function. The iterator takes
407  * ownership of iter0 and iter1 and frees them when the iteration is
408  * over. A derived class should set `ordered` to 1 or 0 based on
409  * whether it generates its output in order by reference name.
410  */
411 struct ref_iterator *merge_ref_iterator_begin(
412 		int ordered,
413 		struct ref_iterator *iter0, struct ref_iterator *iter1,
414 		ref_iterator_select_fn *select, void *cb_data);
415 
416 /*
417  * An iterator consisting of the union of the entries from front and
418  * back. If there are entries common to the two sub-iterators, use the
419  * one from front. Each iterator must iterate over its entries in
420  * strcmp() order by refname for this to work.
421  *
422  * The new iterator takes ownership of its arguments and frees them
423  * when the iteration is over. As a convenience to callers, if front
424  * or back is an empty_ref_iterator, then abort that one immediately
425  * and return the other iterator directly, without wrapping it.
426  */
427 struct ref_iterator *overlay_ref_iterator_begin(
428 		struct ref_iterator *front, struct ref_iterator *back);
429 
430 /*
431  * Wrap iter0, only letting through the references whose names start
432  * with prefix. If trim is set, set iter->refname to the name of the
433  * reference with that many characters trimmed off the front;
434  * otherwise set it to the full refname. The new iterator takes over
435  * ownership of iter0 and frees it when iteration is over. It makes
436  * its own copy of prefix.
437  *
438  * As an convenience to callers, if prefix is the empty string and
439  * trim is zero, this function returns iter0 directly, without
440  * wrapping it.
441  *
442  * The resulting ref_iterator is ordered if iter0 is.
443  */
444 struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
445 					       const char *prefix,
446 					       int trim);
447 
448 /* Internal implementation of reference iteration: */
449 
450 /*
451  * Base class constructor for ref_iterators. Initialize the
452  * ref_iterator part of iter, setting its vtable pointer as specified.
453  * `ordered` should be set to 1 if the iterator will iterate over
454  * references in order by refname; otherwise it should be set to 0.
455  * This is meant to be called only by the initializers of derived
456  * classes.
457  */
458 void base_ref_iterator_init(struct ref_iterator *iter,
459 			    struct ref_iterator_vtable *vtable,
460 			    int ordered);
461 
462 /*
463  * Base class destructor for ref_iterators. Destroy the ref_iterator
464  * part of iter and shallow-free the object. This is meant to be
465  * called only by the destructors of derived classes.
466  */
467 void base_ref_iterator_free(struct ref_iterator *iter);
468 
469 /* Virtual function declarations for ref_iterators: */
470 
471 /*
472  * backend-specific implementation of ref_iterator_advance. For symrefs, the
473  * function should set REF_ISSYMREF, and it should also dereference the symref
474  * to provide the OID referent. It should respect do_for_each_ref_flags
475  * that were passed to refs_ref_iterator_begin().
476  */
477 typedef int ref_iterator_advance_fn(struct ref_iterator *ref_iterator);
478 
479 /*
480  * Peels the current ref, returning 0 for success or -1 for failure.
481  */
482 typedef int ref_iterator_peel_fn(struct ref_iterator *ref_iterator,
483 				 struct object_id *peeled);
484 
485 /*
486  * Implementations of this function should free any resources specific
487  * to the derived class, then call base_ref_iterator_free() to clean
488  * up and free the ref_iterator object.
489  */
490 typedef int ref_iterator_abort_fn(struct ref_iterator *ref_iterator);
491 
492 struct ref_iterator_vtable {
493 	ref_iterator_advance_fn *advance;
494 	ref_iterator_peel_fn *peel;
495 	ref_iterator_abort_fn *abort;
496 };
497 
498 /*
499  * current_ref_iter is a performance hack: when iterating over
500  * references using the for_each_ref*() functions, current_ref_iter is
501  * set to the reference iterator before calling the callback function.
502  * If the callback function calls peel_ref(), then peel_ref() first
503  * checks whether the reference to be peeled is the one referred to by
504  * the iterator (it usually is) and if so, asks the iterator for the
505  * peeled version of the reference if it is available. This avoids a
506  * refname lookup in a common case. current_ref_iter is set to NULL
507  * when the iteration is over.
508  */
509 extern struct ref_iterator *current_ref_iter;
510 
511 /*
512  * The common backend for the for_each_*ref* functions. Call fn for
513  * each reference in iter. If the iterator itself ever returns
514  * ITER_ERROR, return -1. If fn ever returns a non-zero value, stop
515  * the iteration and return that value. Otherwise, return 0. In any
516  * case, free the iterator when done. This function is basically an
517  * adapter between the callback style of reference iteration and the
518  * iterator style.
519  */
520 int do_for_each_repo_ref_iterator(struct repository *r,
521 				  struct ref_iterator *iter,
522 				  each_repo_ref_fn fn, void *cb_data);
523 
524 struct ref_store;
525 
526 /* refs backends */
527 
528 /* ref_store_init flags */
529 #define REF_STORE_READ		(1 << 0)
530 #define REF_STORE_WRITE		(1 << 1) /* can perform update operations */
531 #define REF_STORE_ODB		(1 << 2) /* has access to object database */
532 #define REF_STORE_MAIN		(1 << 3)
533 #define REF_STORE_ALL_CAPS	(REF_STORE_READ | \
534 				 REF_STORE_WRITE | \
535 				 REF_STORE_ODB | \
536 				 REF_STORE_MAIN)
537 
538 /*
539  * Initialize the ref_store for the specified gitdir. These functions
540  * should call base_ref_store_init() to initialize the shared part of
541  * the ref_store and to record the ref_store for later lookup.
542  */
543 typedef struct ref_store *ref_store_init_fn(struct repository *repo,
544 					    const char *gitdir,
545 					    unsigned int flags);
546 
547 typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
548 
549 typedef int ref_transaction_prepare_fn(struct ref_store *refs,
550 				       struct ref_transaction *transaction,
551 				       struct strbuf *err);
552 
553 typedef int ref_transaction_finish_fn(struct ref_store *refs,
554 				      struct ref_transaction *transaction,
555 				      struct strbuf *err);
556 
557 typedef int ref_transaction_abort_fn(struct ref_store *refs,
558 				     struct ref_transaction *transaction,
559 				     struct strbuf *err);
560 
561 typedef int ref_transaction_commit_fn(struct ref_store *refs,
562 				      struct ref_transaction *transaction,
563 				      struct strbuf *err);
564 
565 typedef int pack_refs_fn(struct ref_store *ref_store, unsigned int flags);
566 typedef int create_symref_fn(struct ref_store *ref_store,
567 			     const char *ref_target,
568 			     const char *refs_heads_master,
569 			     const char *logmsg);
570 typedef int delete_refs_fn(struct ref_store *ref_store, const char *msg,
571 			   struct string_list *refnames, unsigned int flags);
572 typedef int rename_ref_fn(struct ref_store *ref_store,
573 			  const char *oldref, const char *newref,
574 			  const char *logmsg);
575 typedef int copy_ref_fn(struct ref_store *ref_store,
576 			  const char *oldref, const char *newref,
577 			  const char *logmsg);
578 
579 /*
580  * Iterate over the references in `ref_store` whose names start with
581  * `prefix`. `prefix` is matched as a literal string, without regard
582  * for path separators. If prefix is NULL or the empty string, iterate
583  * over all references in `ref_store`. The output is ordered by
584  * refname.
585  */
586 typedef struct ref_iterator *ref_iterator_begin_fn(
587 		struct ref_store *ref_store,
588 		const char *prefix, unsigned int flags);
589 
590 /* reflog functions */
591 
592 /*
593  * Iterate over the references in the specified ref_store that have a
594  * reflog. The refs are iterated over in arbitrary order.
595  */
596 typedef struct ref_iterator *reflog_iterator_begin_fn(
597 		struct ref_store *ref_store);
598 
599 typedef int for_each_reflog_ent_fn(struct ref_store *ref_store,
600 				   const char *refname,
601 				   each_reflog_ent_fn fn,
602 				   void *cb_data);
603 typedef int for_each_reflog_ent_reverse_fn(struct ref_store *ref_store,
604 					   const char *refname,
605 					   each_reflog_ent_fn fn,
606 					   void *cb_data);
607 typedef int reflog_exists_fn(struct ref_store *ref_store, const char *refname);
608 typedef int create_reflog_fn(struct ref_store *ref_store, const char *refname,
609 			     int force_create, struct strbuf *err);
610 typedef int delete_reflog_fn(struct ref_store *ref_store, const char *refname);
611 typedef int reflog_expire_fn(struct ref_store *ref_store,
612 			     const char *refname,
613 			     unsigned int flags,
614 			     reflog_expiry_prepare_fn prepare_fn,
615 			     reflog_expiry_should_prune_fn should_prune_fn,
616 			     reflog_expiry_cleanup_fn cleanup_fn,
617 			     void *policy_cb_data);
618 
619 /*
620  * Read a reference from the specified reference store, non-recursively.
621  * Set type to describe the reference, and:
622  *
623  * - If refname is the name of a normal reference, fill in oid
624  *   (leaving referent unchanged).
625  *
626  * - If refname is the name of a symbolic reference, write the full
627  *   name of the reference to which it refers (e.g.
628  *   "refs/heads/master") to referent and set the REF_ISSYMREF bit in
629  *   type (leaving oid unchanged). The caller is responsible for
630  *   validating that referent is a valid reference name.
631  *
632  * WARNING: refname might be used as part of a filename, so it is
633  * important from a security standpoint that it be safe in the sense
634  * of refname_is_safe(). Moreover, for symrefs this function sets
635  * referent to whatever the repository says, which might not be a
636  * properly-formatted or even safe reference name. NEITHER INPUT NOR
637  * OUTPUT REFERENCE NAMES ARE VALIDATED WITHIN THIS FUNCTION.
638  *
639  * Return 0 on success, or -1 on failure. If the ref exists but is neither a
640  * symbolic ref nor an object ID, it is broken. In this case set REF_ISBROKEN in
641  * type, and return -1 (failure_errno should not be ENOENT)
642  *
643  * failure_errno provides errno codes that are interpreted beyond error
644  * reporting. The following error codes have special meaning:
645  *    * ENOENT: the ref doesn't exist
646  *    * EISDIR: ref name is a directory
647  *    * ENOTDIR: ref prefix is not a directory
648  *
649  * Backend-specific flags might be set in type as well, regardless of
650  * outcome.
651  *
652  * It is OK for refname to point into referent. If so:
653  *
654  * - if the function succeeds with REF_ISSYMREF, referent will be
655  *   overwritten and the memory formerly pointed to by it might be
656  *   changed or even freed.
657  *
658  * - in all other cases, referent will be untouched, and therefore
659  *   refname will still be valid and unchanged.
660  */
661 typedef int read_raw_ref_fn(struct ref_store *ref_store, const char *refname,
662 			    struct object_id *oid, struct strbuf *referent,
663 			    unsigned int *type, int *failure_errno);
664 
665 struct ref_storage_be {
666 	struct ref_storage_be *next;
667 	const char *name;
668 	ref_store_init_fn *init;
669 	ref_init_db_fn *init_db;
670 
671 	ref_transaction_prepare_fn *transaction_prepare;
672 	ref_transaction_finish_fn *transaction_finish;
673 	ref_transaction_abort_fn *transaction_abort;
674 	ref_transaction_commit_fn *initial_transaction_commit;
675 
676 	pack_refs_fn *pack_refs;
677 	create_symref_fn *create_symref;
678 	delete_refs_fn *delete_refs;
679 	rename_ref_fn *rename_ref;
680 	copy_ref_fn *copy_ref;
681 
682 	ref_iterator_begin_fn *iterator_begin;
683 	read_raw_ref_fn *read_raw_ref;
684 
685 	reflog_iterator_begin_fn *reflog_iterator_begin;
686 	for_each_reflog_ent_fn *for_each_reflog_ent;
687 	for_each_reflog_ent_reverse_fn *for_each_reflog_ent_reverse;
688 	reflog_exists_fn *reflog_exists;
689 	create_reflog_fn *create_reflog;
690 	delete_reflog_fn *delete_reflog;
691 	reflog_expire_fn *reflog_expire;
692 };
693 
694 extern struct ref_storage_be refs_be_files;
695 extern struct ref_storage_be refs_be_packed;
696 
697 /*
698  * A representation of the reference store for the main repository or
699  * a submodule. The ref_store instances for submodules are kept in a
700  * hash map; see get_submodule_ref_store() for more info.
701  */
702 struct ref_store {
703 	/* The backend describing this ref_store's storage scheme: */
704 	const struct ref_storage_be *be;
705 
706 	struct repository *repo;
707 
708 	/*
709 	 * The gitdir that this ref_store applies to. Note that this is not
710 	 * necessarily repo->gitdir if the repo has multiple worktrees.
711 	 */
712 	char *gitdir;
713 };
714 
715 /*
716  * Parse contents of a loose ref file.
717  */
718 int parse_loose_ref_contents(const char *buf, struct object_id *oid,
719 			     struct strbuf *referent, unsigned int *type);
720 
721 /*
722  * Fill in the generic part of refs and add it to our collection of
723  * reference stores.
724  */
725 void base_ref_store_init(struct ref_store *refs,
726 			 const struct ref_storage_be *be);
727 
728 /*
729  * Support GIT_TRACE_REFS by optionally wrapping the given ref_store instance.
730  */
731 struct ref_store *maybe_debug_wrap_ref_store(const char *gitdir, struct ref_store *store);
732 
733 #endif /* REFS_REFS_INTERNAL_H */
734