git/refs.c

/*
 * The backend-independent part of the reference module.
 */

#include "cache.h"
#include "config.h"
#include "hashmap.h"
#include "lockfile.h"
#include "iterator.h"
#include "refs.h"
#include "refs/refs-internal.h"
#include "run-command.h"
#include "object-store.h"
#include "object.h"
#include "tag.h"
#include "submodule.h"
#include "worktree.h"
#include "argv-array.h"
#include "repository.h"
#include "sigchain.h"

/*
 * List of all available backends
 */
static struct ref_storage_be *refs_backends = &refs_be_files;

static struct ref_storage_be *find_ref_storage_backend(const char *name)
{
	struct ref_storage_be *be;
	for (be = refs_backends; be; be = be->next)
		if (!strcmp(be->name, name))
			return be;
	return NULL;
}

int ref_storage_backend_exists(const char *name)
{
	return find_ref_storage_backend(name) != NULL;
}

/*
 * How to handle various characters in refnames:
 * 0: An acceptable character for refs
 * 1: End-of-component
 * 2: ., look for a preceding . to reject .. in refs
 * 3: {, look for a preceding @ to reject @{ in refs
 * 4: A bad character: ASCII control characters, and
 *    ":", "?", "[", "\", "^", "~", SP, or TAB
 * 5: *, reject unless REFNAME_REFSPEC_PATTERN is set
 */
static unsigned char refname_disposition[256] = {
	1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
	4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 2, 1,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 4,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 4, 0, 4, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 4, 4
};

/*
 * Try to read one refname component from the front of refname.
 * Return the length of the component found, or -1 if the component is
 * not legal.  It is legal if it is something reasonable to have under
 * ".git/refs/"; We do not like it if:
 *
 * - it begins with ".", or
 * - it has double dots "..", or
 * - it has ASCII control characters, or
 * - it has ":", "?", "[", "\", "^", "~", SP, or TAB anywhere, or
 * - it has "*" anywhere unless REFNAME_REFSPEC_PATTERN is set, or
 * - it ends with a "/", or
 * - it ends with ".lock", or
 * - it contains a "@{" portion
 *
 * When sanitized is not NULL, instead of rejecting the input refname
 * as an error, try to come up with a usable replacement for the input
 * refname in it.
 */
static int check_refname_component(const char *refname, int *flags,
				   struct strbuf *sanitized)
{
	const char *cp;
	char last = '\0';
	size_t component_start = 0; /* garbage - not a reasonable initial value */

	if (sanitized)
		component_start = sanitized->len;

	for (cp = refname; ; cp++) {
		int ch = *cp & 255;
		unsigned char disp = refname_disposition[ch];

		if (sanitized && disp != 1)
			strbuf_addch(sanitized, ch);

		switch (disp) {
		case 1:
			goto out;
		case 2:
			if (last == '.') { /* Refname contains "..". */
				if (sanitized)
					/* collapse ".." to single "." */
					strbuf_setlen(sanitized, sanitized->len - 1);
				else
					return -1;
			}
			break;
		case 3:
			if (last == '@') { /* Refname contains "@{". */
				if (sanitized)
					sanitized->buf[sanitized->len-1] = '-';
				else
					return -1;
			}
			break;
		case 4:
			/* forbidden char */
			if (sanitized)
				sanitized->buf[sanitized->len-1] = '-';
			else
				return -1;
			break;
		case 5:
			if (!(*flags & REFNAME_REFSPEC_PATTERN)) {
				/* refspec can't be a pattern */
				if (sanitized)
					sanitized->buf[sanitized->len-1] = '-';
				else
					return -1;
			}

			/*
			 * Unset the pattern flag so that we only accept
			 * a single asterisk for one side of refspec.
			 */
			*flags &= ~ REFNAME_REFSPEC_PATTERN;
			break;
		}
		last = ch;
	}
out:
	if (cp == refname)
		return 0; /* Component has zero length. */

	if (refname[0] == '.') { /* Component starts with '.'. */
		if (sanitized)
			sanitized->buf[component_start] = '-';
		else
			return -1;
	}
	if (cp - refname >= LOCK_SUFFIX_LEN &&
	    !memcmp(cp - LOCK_SUFFIX_LEN, LOCK_SUFFIX, LOCK_SUFFIX_LEN)) {
		if (!sanitized)
			return -1;
		/* Refname ends with ".lock". */
		while (strbuf_strip_suffix(sanitized, LOCK_SUFFIX)) {
			/* try again in case we have .lock.lock */
		}
	}
	return cp - refname;
}

static int check_or_sanitize_refname(const char *refname, int flags,
				     struct strbuf *sanitized)
{
	int component_len, component_count = 0;

	if (!strcmp(refname, "@")) {
		/* Refname is a single character '@'. */
		if (sanitized)
			strbuf_addch(sanitized, '-');
		else
			return -1;
	}

	while (1) {
		if (sanitized && sanitized->len)
			strbuf_complete(sanitized, '/');

		/* We are at the start of a path component. */
		component_len = check_refname_component(refname, &flags,
							sanitized);
		if (sanitized && component_len == 0)
			; /* OK, omit empty component */
		else if (component_len <= 0)
			return -1;

		component_count++;
		if (refname[component_len] == '\0')
			break;
		/* Skip to next component. */
		refname += component_len + 1;
	}

	if (refname[component_len - 1] == '.') {
		/* Refname ends with '.'. */
		if (sanitized)
			; /* omit ending dot */
		else
			return -1;
	}
	if (!(flags & REFNAME_ALLOW_ONELEVEL) && component_count < 2)
		return -1; /* Refname has only one component. */
	return 0;
}

int check_refname_format(const char *refname, int flags)
{
	return check_or_sanitize_refname(refname, flags, NULL);
}

void sanitize_refname_component(const char *refname, struct strbuf *out)
{
	if (check_or_sanitize_refname(refname, REFNAME_ALLOW_ONELEVEL, out))
		BUG("sanitizing refname '%s' check returned error", refname);
}

int refname_is_safe(const char *refname)
{
	const char *rest;

	if (skip_prefix(refname, "refs/", &rest)) {
		char *buf;
		int result;
		size_t restlen = strlen(rest);

		/* rest must not be empty, or start or end with "/" */
		if (!restlen || *rest == '/' || rest[restlen - 1] == '/')
			return 0;

		/*
		 * Does the refname try to escape refs/?
		 * For example: refs/foo/../bar is safe but refs/foo/../../bar
		 * is not.
		 */
		buf = xmallocz(restlen);
		result = !normalize_path_copy(buf, rest) && !strcmp(buf, rest);
		free(buf);
		return result;
	}

	do {
		if (!isupper(*refname) && *refname != '_')
			return 0;
		refname++;
	} while (*refname);
	return 1;
}

/*
 * Return true if refname, which has the specified oid and flags, can
 * be resolved to an object in the database. If the referred-to object
 * does not exist, emit a warning and return false.
 */
int ref_resolves_to_object(const char *refname,
			   const struct object_id *oid,
			   unsigned int flags)
{
	if (flags & REF_ISBROKEN)
		return 0;
	if (!has_object_file(oid)) {
		error(_("%s does not point to a valid object!"), refname);
		return 0;
	}
	return 1;
}

char *refs_resolve_refdup(struct ref_store *refs,
			  const char *refname, int resolve_flags,
			  struct object_id *oid, int *flags)
{
	const char *result;

	result = refs_resolve_ref_unsafe(refs, refname, resolve_flags,
					 oid, flags);
	return xstrdup_or_null(result);
}

char *resolve_refdup(const char *refname, int resolve_flags,
		     struct object_id *oid, int *flags)
{
	return refs_resolve_refdup(get_main_ref_store(the_repository),
				   refname, resolve_flags,
				   oid, flags);
}

/* The argument to filter_refs */
struct ref_filter {
	const char *pattern;
	const char *prefix;
	each_ref_fn *fn;
	void *cb_data;
};

int refs_read_ref_full(struct ref_store *refs, const char *refname,
		       int resolve_flags, struct object_id *oid, int *flags)
{
	if (refs_resolve_ref_unsafe(refs, refname, resolve_flags, oid, flags))
		return 0;
	return -1;
}

int read_ref_full(const char *refname, int resolve_flags, struct object_id *oid, int *flags)
{
	return refs_read_ref_full(get_main_ref_store(the_repository), refname,
				  resolve_flags, oid, flags);
}

int read_ref(const char *refname, struct object_id *oid)
{
	return read_ref_full(refname, RESOLVE_REF_READING, oid, NULL);
}

static int refs_ref_exists(struct ref_store *refs, const char *refname)
{
	return !!refs_resolve_ref_unsafe(refs, refname, RESOLVE_REF_READING, NULL, NULL);
}

int ref_exists(const char *refname)
{
	return refs_ref_exists(get_main_ref_store(the_repository), refname);
}

static int filter_refs(const char *refname, const struct object_id *oid,
			   int flags, void *data)
{
	struct ref_filter *filter = (struct ref_filter *)data;

	if (wildmatch(filter->pattern, refname, 0))
		return 0;
	if (filter->prefix)
		skip_prefix(refname, filter->prefix, &refname);
	return filter->fn(refname, oid, flags, filter->cb_data);
}

enum peel_status peel_object(const struct object_id *name, struct object_id *oid)
{
	struct object *o = lookup_unknown_object(name);

	if (o->type == OBJ_NONE) {
		int type = oid_object_info(the_repository, name, NULL);
		if (type < 0 || !object_as_type(o, type, 0))
			return PEEL_INVALID;
	}

	if (o->type != OBJ_TAG)
		return PEEL_NON_TAG;

	o = deref_tag_noverify(o);
	if (!o)
		return PEEL_INVALID;

	oidcpy(oid, &o->oid);
	return PEEL_PEELED;
}

struct warn_if_dangling_data {
	FILE *fp;
	const char *refname;
	const struct string_list *refnames;
	const char *msg_fmt;
};

static int warn_if_dangling_symref(const char *refname, const struct object_id *oid,
				   int flags, void *cb_data)
{
	struct warn_if_dangling_data *d = cb_data;
	const char *resolves_to;

	if (!(flags & REF_ISSYMREF))
		return 0;

	resolves_to = resolve_ref_unsafe(refname, 0, NULL, NULL);
	if (!resolves_to
	    || (d->refname
		? strcmp(resolves_to, d->refname)
		: !string_list_has_string(d->refnames, resolves_to))) {
		return 0;
	}

	fprintf(d->fp, d->msg_fmt, refname);
	fputc('\n', d->fp);
	return 0;
}

void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname)
{
	struct warn_if_dangling_data data;

	data.fp = fp;
	data.refname = refname;
	data.refnames = NULL;
	data.msg_fmt = msg_fmt;
	for_each_rawref(warn_if_dangling_symref, &data);
}

void warn_dangling_symrefs(FILE *fp, const char *msg_fmt, const struct string_list *refnames)
{
	struct warn_if_dangling_data data;

	data.fp = fp;
	data.refname = NULL;
	data.refnames = refnames;
	data.msg_fmt = msg_fmt;
	for_each_rawref(warn_if_dangling_symref, &data);
}

int refs_for_each_tag_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	return refs_for_each_ref_in(refs, "refs/tags/", fn, cb_data);
}

int for_each_tag_ref(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_tag_ref(get_main_ref_store(the_repository), fn, cb_data);
}

int refs_for_each_branch_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	return refs_for_each_ref_in(refs, "refs/heads/", fn, cb_data);
}

int for_each_branch_ref(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_branch_ref(get_main_ref_store(the_repository), fn, cb_data);
}

int refs_for_each_remote_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	return refs_for_each_ref_in(refs, "refs/remotes/", fn, cb_data);
}

int for_each_remote_ref(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_remote_ref(get_main_ref_store(the_repository), fn, cb_data);
}

int head_ref_namespaced(each_ref_fn fn, void *cb_data)
{
	struct strbuf buf = STRBUF_INIT;
	int ret = 0;
	struct object_id oid;
	int flag;

	strbuf_addf(&buf, "%sHEAD", get_git_namespace());
	if (!read_ref_full(buf.buf, RESOLVE_REF_READING, &oid, &flag))
		ret = fn(buf.buf, &oid, flag, cb_data);
	strbuf_release(&buf);

	return ret;
}

void normalize_glob_ref(struct string_list_item *item, const char *prefix,
			const char *pattern)
{
	struct strbuf normalized_pattern = STRBUF_INIT;

	if (*pattern == '/')
		BUG("pattern must not start with '/'");

	if (prefix) {
		strbuf_addstr(&normalized_pattern, prefix);
	}
	else if (!starts_with(pattern, "refs/"))
		strbuf_addstr(&normalized_pattern, "refs/");
	strbuf_addstr(&normalized_pattern, pattern);
	strbuf_strip_suffix(&normalized_pattern, "/");

	item->string = strbuf_detach(&normalized_pattern, NULL);
	item->util = has_glob_specials(pattern) ? NULL : item->string;
	strbuf_release(&normalized_pattern);
}

int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
	const char *prefix, void *cb_data)
{
	struct strbuf real_pattern = STRBUF_INIT;
	struct ref_filter filter;
	int ret;

	if (!prefix && !starts_with(pattern, "refs/"))
		strbuf_addstr(&real_pattern, "refs/");
	else if (prefix)
		strbuf_addstr(&real_pattern, prefix);
	strbuf_addstr(&real_pattern, pattern);

	if (!has_glob_specials(pattern)) {
		/* Append implied '/' '*' if not present. */
		strbuf_complete(&real_pattern, '/');
		/* No need to check for '*', there is none. */
		strbuf_addch(&real_pattern, '*');
	}

	filter.pattern = real_pattern.buf;
	filter.prefix = prefix;
	filter.fn = fn;
	filter.cb_data = cb_data;
	ret = for_each_ref(filter_refs, &filter);

	strbuf_release(&real_pattern);
	return ret;
}

int for_each_glob_ref(each_ref_fn fn, const char *pattern, void *cb_data)
{
	return for_each_glob_ref_in(fn, pattern, NULL, cb_data);
}

const char *prettify_refname(const char *name)
{
	if (skip_prefix(name, "refs/heads/", &name) ||
	    skip_prefix(name, "refs/tags/", &name) ||
	    skip_prefix(name, "refs/remotes/", &name))
		; /* nothing */
	return name;
}

static const char *ref_rev_parse_rules[] = {
	"%.*s",
	"refs/%.*s",
	"refs/tags/%.*s",
	"refs/heads/%.*s",
	"refs/remotes/%.*s",
	"refs/remotes/%.*s/HEAD",
	NULL
};

#define NUM_REV_PARSE_RULES (ARRAY_SIZE(ref_rev_parse_rules) - 1)

/*
 * Is it possible that the caller meant full_name with abbrev_name?
 * If so return a non-zero value to signal "yes"; the magnitude of
 * the returned value gives the precedence used for disambiguation.
 *
 * If abbrev_name cannot mean full_name, return 0.
 */
int refname_match(const char *abbrev_name, const char *full_name)
{
	const char **p;
	const int abbrev_name_len = strlen(abbrev_name);
	const int num_rules = NUM_REV_PARSE_RULES;

	for (p = ref_rev_parse_rules; *p; p++)
		if (!strcmp(full_name, mkpath(*p, abbrev_name_len, abbrev_name)))
			return &ref_rev_parse_rules[num_rules] - p;

	return 0;
}

/*
 * Given a 'prefix' expand it by the rules in 'ref_rev_parse_rules' and add
 * the results to 'prefixes'
 */
void expand_ref_prefix(struct argv_array *prefixes, const char *prefix)
{
	const char **p;
	int len = strlen(prefix);

	for (p = ref_rev_parse_rules; *p; p++)
		argv_array_pushf(prefixes, *p, len, prefix);
}

char *repo_default_branch_name(struct repository *r)
{
	const char *config_key = "init.defaultbranch";
	const char *config_display_key = "init.defaultBranch";
	char *ret = NULL, *full_ref;

	if (repo_config_get_string(r, config_key, &ret) < 0)
		die(_("could not retrieve `%s`"), config_display_key);

	if (!ret)
		ret = xstrdup("master");

	full_ref = xstrfmt("refs/heads/%s", ret);
	if (check_refname_format(full_ref, 0))
		die(_("invalid branch name: %s = %s"), config_display_key, ret);
	free(full_ref);

	return ret;
}

const char *git_default_branch_name(void)
{
	static char *ret;

	if (!ret)
		ret = repo_default_branch_name(the_repository);

	return ret;
}

/*
 * *string and *len will only be substituted, and *string returned (for
 * later free()ing) if the string passed in is a magic short-hand form
 * to name a branch.
 */
static char *substitute_branch_name(struct repository *r,
				    const char **string, int *len)
{
	struct strbuf buf = STRBUF_INIT;
	int ret = repo_interpret_branch_name(r, *string, *len, &buf, 0);

	if (ret == *len) {
		size_t size;
		*string = strbuf_detach(&buf, &size);
		*len = size;
		return (char *)*string;
	}

	return NULL;
}

int repo_dwim_ref(struct repository *r, const char *str, int len,
		  struct object_id *oid, char **ref)
{
	char *last_branch = substitute_branch_name(r, &str, &len);
	int   refs_found  = expand_ref(r, str, len, oid, ref);
	free(last_branch);
	return refs_found;
}

int dwim_ref(const char *str, int len, struct object_id *oid, char **ref)
{
	return repo_dwim_ref(the_repository, str, len, oid, ref);
}

int expand_ref(struct repository *repo, const char *str, int len,
	       struct object_id *oid, char **ref)
{
	const char **p, *r;
	int refs_found = 0;
	struct strbuf fullref = STRBUF_INIT;

	*ref = NULL;
	for (p = ref_rev_parse_rules; *p; p++) {
		struct object_id oid_from_ref;
		struct object_id *this_result;
		int flag;

		this_result = refs_found ? &oid_from_ref : oid;
		strbuf_reset(&fullref);
		strbuf_addf(&fullref, *p, len, str);
		r = refs_resolve_ref_unsafe(get_main_ref_store(repo),
					    fullref.buf, RESOLVE_REF_READING,
					    this_result, &flag);
		if (r) {
			if (!refs_found++)
				*ref = xstrdup(r);
			if (!warn_ambiguous_refs)
				break;
		} else if ((flag & REF_ISSYMREF) && strcmp(fullref.buf, "HEAD")) {
			warning(_("ignoring dangling symref %s"), fullref.buf);
		} else if ((flag & REF_ISBROKEN) && strchr(fullref.buf, '/')) {
			warning(_("ignoring broken ref %s"), fullref.buf);
		}
	}
	strbuf_release(&fullref);
	return refs_found;
}

int repo_dwim_log(struct repository *r, const char *str, int len,
		  struct object_id *oid, char **log)
{
	struct ref_store *refs = get_main_ref_store(r);
	char *last_branch = substitute_branch_name(r, &str, &len);
	const char **p;
	int logs_found = 0;
	struct strbuf path = STRBUF_INIT;

	*log = NULL;
	for (p = ref_rev_parse_rules; *p; p++) {
		struct object_id hash;
		const char *ref, *it;

		strbuf_reset(&path);
		strbuf_addf(&path, *p, len, str);
		ref = refs_resolve_ref_unsafe(refs, path.buf,
					      RESOLVE_REF_READING,
					      &hash, NULL);
		if (!ref)
			continue;
		if (refs_reflog_exists(refs, path.buf))
			it = path.buf;
		else if (strcmp(ref, path.buf) &&
			 refs_reflog_exists(refs, ref))
			it = ref;
		else
			continue;
		if (!logs_found++) {
			*log = xstrdup(it);
			oidcpy(oid, &hash);
		}
		if (!warn_ambiguous_refs)
			break;
	}
	strbuf_release(&path);
	free(last_branch);
	return logs_found;
}

int dwim_log(const char *str, int len, struct object_id *oid, char **log)
{
	return repo_dwim_log(the_repository, str, len, oid, log);
}

static int is_per_worktree_ref(const char *refname)
{
	return !strcmp(refname, "HEAD") ||
		starts_with(refname, "refs/worktree/") ||
		starts_with(refname, "refs/bisect/") ||
		starts_with(refname, "refs/rewritten/");
}

static int is_pseudoref_syntax(const char *refname)
{
	const char *c;

	for (c = refname; *c; c++) {
		if (!isupper(*c) && *c != '-' && *c != '_')
			return 0;
	}

	return 1;
}

static int is_main_pseudoref_syntax(const char *refname)
{
	return skip_prefix(refname, "main-worktree/", &refname) &&
		*refname &&
		is_pseudoref_syntax(refname);
}

static int is_other_pseudoref_syntax(const char *refname)
{
	if (!skip_prefix(refname, "worktrees/", &refname))
		return 0;
	refname = strchr(refname, '/');
	if (!refname || !refname[1])
		return 0;
	return is_pseudoref_syntax(refname + 1);
}

enum ref_type ref_type(const char *refname)
{
	if (is_per_worktree_ref(refname))
		return REF_TYPE_PER_WORKTREE;
	if (is_pseudoref_syntax(refname))
		return REF_TYPE_PSEUDOREF;
	if (is_main_pseudoref_syntax(refname))
		return REF_TYPE_MAIN_PSEUDOREF;
	if (is_other_pseudoref_syntax(refname))
		return REF_TYPE_OTHER_PSEUDOREF;
	return REF_TYPE_NORMAL;
}

long get_files_ref_lock_timeout_ms(void)
{
	static int configured = 0;

	/* The default timeout is 100 ms: */
	static int timeout_ms = 100;

	if (!configured) {
		git_config_get_int("core.filesreflocktimeout", &timeout_ms);
		configured = 1;
	}

	return timeout_ms;
}

static int write_pseudoref(const char *pseudoref, const struct object_id *oid,
			   const struct object_id *old_oid, struct strbuf *err)
{
	const char *filename;
	int fd;
	struct lock_file lock = LOCK_INIT;
	struct strbuf buf = STRBUF_INIT;
	int ret = -1;

	if (!oid)
		return 0;

	strbuf_addf(&buf, "%s\n", oid_to_hex(oid));

	filename = git_path("%s", pseudoref);
	fd = hold_lock_file_for_update_timeout(&lock, filename, 0,
					       get_files_ref_lock_timeout_ms());
	if (fd < 0) {
		strbuf_addf(err, _("could not open '%s' for writing: %s"),
			    filename, strerror(errno));
		goto done;
	}

	if (old_oid) {
		struct object_id actual_old_oid;

		if (read_ref(pseudoref, &actual_old_oid)) {
			if (!is_null_oid(old_oid)) {
				strbuf_addf(err, _("could not read ref '%s'"),
					    pseudoref);
				rollback_lock_file(&lock);
				goto done;
			}
		} else if (is_null_oid(old_oid)) {
			strbuf_addf(err, _("ref '%s' already exists"),
				    pseudoref);
			rollback_lock_file(&lock);
			goto done;
		} else if (!oideq(&actual_old_oid, old_oid)) {
			strbuf_addf(err, _("unexpected object ID when writing '%s'"),
				    pseudoref);
			rollback_lock_file(&lock);
			goto done;
		}
	}

	if (write_in_full(fd, buf.buf, buf.len) < 0) {
		strbuf_addf(err, _("could not write to '%s'"), filename);
		rollback_lock_file(&lock);
		goto done;
	}

	commit_lock_file(&lock);
	ret = 0;
done:
	strbuf_release(&buf);
	return ret;
}

static int delete_pseudoref(const char *pseudoref, const struct object_id *old_oid)
{
	const char *filename;

	filename = git_path("%s", pseudoref);

	if (old_oid && !is_null_oid(old_oid)) {
		struct lock_file lock = LOCK_INIT;
		int fd;
		struct object_id actual_old_oid;

		fd = hold_lock_file_for_update_timeout(
				&lock, filename, 0,
				get_files_ref_lock_timeout_ms());
		if (fd < 0) {
			error_errno(_("could not open '%s' for writing"),
				    filename);
			return -1;
		}
		if (read_ref(pseudoref, &actual_old_oid))
			die(_("could not read ref '%s'"), pseudoref);
		if (!oideq(&actual_old_oid, old_oid)) {
			error(_("unexpected object ID when deleting '%s'"),
			      pseudoref);
			rollback_lock_file(&lock);
			return -1;
		}

		unlink(filename);
		rollback_lock_file(&lock);
	} else {
		unlink(filename);
	}

	return 0;
}

int refs_delete_ref(struct ref_store *refs, const char *msg,
		    const char *refname,
		    const struct object_id *old_oid,
		    unsigned int flags)
{
	struct ref_transaction *transaction;
	struct strbuf err = STRBUF_INIT;

	if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
		assert(refs == get_main_ref_store(the_repository));
		return delete_pseudoref(refname, old_oid);
	}

	transaction = ref_store_transaction_begin(refs, &err);
	if (!transaction ||
	    ref_transaction_delete(transaction, refname, old_oid,
				   flags, msg, &err) ||
	    ref_transaction_commit(transaction, &err)) {
		error("%s", err.buf);
		ref_transaction_free(transaction);
		strbuf_release(&err);
		return 1;
	}
	ref_transaction_free(transaction);
	strbuf_release(&err);
	return 0;
}

int delete_ref(const char *msg, const char *refname,
	       const struct object_id *old_oid, unsigned int flags)
{
	return refs_delete_ref(get_main_ref_store(the_repository), msg, refname,
			       old_oid, flags);
}

void copy_reflog_msg(struct strbuf *sb, const char *msg)
{
	char c;
	int wasspace = 1;

	strbuf_addch(sb, '\t');
	while ((c = *msg++)) {
		if (wasspace && isspace(c))
			continue;
		wasspace = isspace(c);
		if (wasspace)
			c = ' ';
		strbuf_addch(sb, c);
	}
	strbuf_rtrim(sb);
}

int should_autocreate_reflog(const char *refname)
{
	switch (log_all_ref_updates) {
	case LOG_REFS_ALWAYS:
		return 1;
	case LOG_REFS_NORMAL:
		return starts_with(refname, "refs/heads/") ||
			starts_with(refname, "refs/remotes/") ||
			starts_with(refname, "refs/notes/") ||
			!strcmp(refname, "HEAD");
	default:
		return 0;
	}
}

int is_branch(const char *refname)
{
	return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
}

struct read_ref_at_cb {
	const char *refname;
	timestamp_t at_time;
	int cnt;
	int reccnt;
	struct object_id *oid;
	int found_it;

	struct object_id ooid;
	struct object_id noid;
	int tz;
	timestamp_t date;
	char **msg;
	timestamp_t *cutoff_time;
	int *cutoff_tz;
	int *cutoff_cnt;
};

static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
		const char *email, timestamp_t timestamp, int tz,
		const char *message, void *cb_data)
{
	struct read_ref_at_cb *cb = cb_data;

	cb->reccnt++;
	cb->tz = tz;
	cb->date = timestamp;

	if (timestamp <= cb->at_time || cb->cnt == 0) {
		if (cb->msg)
			*cb->msg = xstrdup(message);
		if (cb->cutoff_time)
			*cb->cutoff_time = timestamp;
		if (cb->cutoff_tz)
			*cb->cutoff_tz = tz;
		if (cb->cutoff_cnt)
			*cb->cutoff_cnt = cb->reccnt - 1;
		/*
		 * we have not yet updated cb->[n|o]oid so they still
		 * hold the values for the previous record.
		 */
		if (!is_null_oid(&cb->ooid)) {
			oidcpy(cb->oid, noid);
			if (!oideq(&cb->ooid, noid))
				warning(_("log for ref %s has gap after %s"),
					cb->refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
		}
		else if (cb->date == cb->at_time)
			oidcpy(cb->oid, noid);
		else if (!oideq(noid, cb->oid))
			warning(_("log for ref %s unexpectedly ended on %s"),
				cb->refname, show_date(cb->date, cb->tz,
						       DATE_MODE(RFC2822)));
		oidcpy(&cb->ooid, ooid);
		oidcpy(&cb->noid, noid);
		cb->found_it = 1;
		return 1;
	}
	oidcpy(&cb->ooid, ooid);
	oidcpy(&cb->noid, noid);
	if (cb->cnt > 0)
		cb->cnt--;
	return 0;
}

static int read_ref_at_ent_oldest(struct object_id *ooid, struct object_id *noid,
				  const char *email, timestamp_t timestamp,
				  int tz, const char *message, void *cb_data)
{
	struct read_ref_at_cb *cb = cb_data;

	if (cb->msg)
		*cb->msg = xstrdup(message);
	if (cb->cutoff_time)
		*cb->cutoff_time = timestamp;
	if (cb->cutoff_tz)
		*cb->cutoff_tz = tz;
	if (cb->cutoff_cnt)
		*cb->cutoff_cnt = cb->reccnt;
	oidcpy(cb->oid, ooid);
	if (is_null_oid(cb->oid))
		oidcpy(cb->oid, noid);
	/* We just want the first entry */
	return 1;
}

int read_ref_at(struct ref_store *refs, const char *refname,
		unsigned int flags, timestamp_t at_time, int cnt,
		struct object_id *oid, char **msg,
		timestamp_t *cutoff_time, int *cutoff_tz, int *cutoff_cnt)
{
	struct read_ref_at_cb cb;

	memset(&cb, 0, sizeof(cb));
	cb.refname = refname;
	cb.at_time = at_time;
	cb.cnt = cnt;
	cb.msg = msg;
	cb.cutoff_time = cutoff_time;
	cb.cutoff_tz = cutoff_tz;
	cb.cutoff_cnt = cutoff_cnt;
	cb.oid = oid;

	refs_for_each_reflog_ent_reverse(refs, refname, read_ref_at_ent, &cb);

	if (!cb.reccnt) {
		if (flags & GET_OID_QUIETLY)
			exit(128);
		else
			die(_("log for %s is empty"), refname);
	}
	if (cb.found_it)
		return 0;

	refs_for_each_reflog_ent(refs, refname, read_ref_at_ent_oldest, &cb);

	return 1;
}

struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
						    struct strbuf *err)
{
	struct ref_transaction *tr;
	assert(err);

	tr = xcalloc(1, sizeof(struct ref_transaction));
	tr->ref_store = refs;
	return tr;
}

struct ref_transaction *ref_transaction_begin(struct strbuf *err)
{
	return ref_store_transaction_begin(get_main_ref_store(the_repository), err);
}

void ref_transaction_free(struct ref_transaction *transaction)
{
	size_t i;

	if (!transaction)
		return;

	switch (transaction->state) {
	case REF_TRANSACTION_OPEN:
	case REF_TRANSACTION_CLOSED:
		/* OK */
		break;
	case REF_TRANSACTION_PREPARED:
		BUG("free called on a prepared reference transaction");
		break;
	default:
		BUG("unexpected reference transaction state");
		break;
	}

	for (i = 0; i < transaction->nr; i++) {
		free(transaction->updates[i]->msg);
		free(transaction->updates[i]);
	}
	free(transaction->updates);
	free(transaction);
}

struct ref_update *ref_transaction_add_update(
		struct ref_transaction *transaction,
		const char *refname, unsigned int flags,
		const struct object_id *new_oid,
		const struct object_id *old_oid,
		const char *msg)
{
	struct ref_update *update;

	if (transaction->state != REF_TRANSACTION_OPEN)
		BUG("update called for transaction that is not open");

	FLEX_ALLOC_STR(update, refname, refname);
	ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
	transaction->updates[transaction->nr++] = update;

	update->flags = flags;

	if (flags & REF_HAVE_NEW)
		oidcpy(&update->new_oid, new_oid);
	if (flags & REF_HAVE_OLD)
		oidcpy(&update->old_oid, old_oid);
	update->msg = xstrdup_or_null(msg);
	return update;
}

int ref_transaction_update(struct ref_transaction *transaction,
			   const char *refname,
			   const struct object_id *new_oid,
			   const struct object_id *old_oid,
			   unsigned int flags, const char *msg,
			   struct strbuf *err)
{
	assert(err);

	if ((new_oid && !is_null_oid(new_oid)) ?
	    check_refname_format(refname, REFNAME_ALLOW_ONELEVEL) :
	    !refname_is_safe(refname)) {
		strbuf_addf(err, _("refusing to update ref with bad name '%s'"),
			    refname);
		return -1;
	}

	if (flags & ~REF_TRANSACTION_UPDATE_ALLOWED_FLAGS)
		BUG("illegal flags 0x%x passed to ref_transaction_update()", flags);

	flags |= (new_oid ? REF_HAVE_NEW : 0) | (old_oid ? REF_HAVE_OLD : 0);

	ref_transaction_add_update(transaction, refname, flags,
				   new_oid, old_oid, msg);
	return 0;
}

int ref_transaction_create(struct ref_transaction *transaction,
			   const char *refname,
			   const struct object_id *new_oid,
			   unsigned int flags, const char *msg,
			   struct strbuf *err)
{
	if (!new_oid || is_null_oid(new_oid))
		BUG("create called without valid new_oid");
	return ref_transaction_update(transaction, refname, new_oid,
				      &null_oid, flags, msg, err);
}

int ref_transaction_delete(struct ref_transaction *transaction,
			   const char *refname,
			   const struct object_id *old_oid,
			   unsigned int flags, const char *msg,
			   struct strbuf *err)
{
	if (old_oid && is_null_oid(old_oid))
		BUG("delete called with old_oid set to zeros");
	return ref_transaction_update(transaction, refname,
				      &null_oid, old_oid,
				      flags, msg, err);
}

int ref_transaction_verify(struct ref_transaction *transaction,
			   const char *refname,
			   const struct object_id *old_oid,
			   unsigned int flags,
			   struct strbuf *err)
{
	if (!old_oid)
		BUG("verify called with old_oid set to NULL");
	return ref_transaction_update(transaction, refname,
				      NULL, old_oid,
				      flags, NULL, err);
}

int refs_update_ref(struct ref_store *refs, const char *msg,
		    const char *refname, const struct object_id *new_oid,
		    const struct object_id *old_oid, unsigned int flags,
		    enum action_on_err onerr)
{
	struct ref_transaction *t = NULL;
	struct strbuf err = STRBUF_INIT;
	int ret = 0;

	if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
		assert(refs == get_main_ref_store(the_repository));
		ret = write_pseudoref(refname, new_oid, old_oid, &err);
	} else {
		t = ref_store_transaction_begin(refs, &err);
		if (!t ||
		    ref_transaction_update(t, refname, new_oid, old_oid,
					   flags, msg, &err) ||
		    ref_transaction_commit(t, &err)) {
			ret = 1;
			ref_transaction_free(t);
		}
	}
	if (ret) {
		const char *str = _("update_ref failed for ref '%s': %s");

		switch (onerr) {
		case UPDATE_REFS_MSG_ON_ERR:
			error(str, refname, err.buf);
			break;
		case UPDATE_REFS_DIE_ON_ERR:
			die(str, refname, err.buf);
			break;
		case UPDATE_REFS_QUIET_ON_ERR:
			break;
		}
		strbuf_release(&err);
		return 1;
	}
	strbuf_release(&err);
	if (t)
		ref_transaction_free(t);
	return 0;
}

int update_ref(const char *msg, const char *refname,
	       const struct object_id *new_oid,
	       const struct object_id *old_oid,
	       unsigned int flags, enum action_on_err onerr)
{
	return refs_update_ref(get_main_ref_store(the_repository), msg, refname, new_oid,
			       old_oid, flags, onerr);
}

char *refs_shorten_unambiguous_ref(struct ref_store *refs,
				   const char *refname, int strict)
{
	int i;
	static char **scanf_fmts;
	static int nr_rules;
	char *short_name;
	struct strbuf resolved_buf = STRBUF_INIT;

	if (!nr_rules) {
		/*
		 * Pre-generate scanf formats from ref_rev_parse_rules[].
		 * Generate a format suitable for scanf from a
		 * ref_rev_parse_rules rule by interpolating "%s" at the
		 * location of the "%.*s".
		 */
		size_t total_len = 0;
		size_t offset = 0;

		/* the rule list is NULL terminated, count them first */
		for (nr_rules = 0; ref_rev_parse_rules[nr_rules]; nr_rules++)
			/* -2 for strlen("%.*s") - strlen("%s"); +1 for NUL */
			total_len += strlen(ref_rev_parse_rules[nr_rules]) - 2 + 1;

		scanf_fmts = xmalloc(st_add(st_mult(sizeof(char *), nr_rules), total_len));

		offset = 0;
		for (i = 0; i < nr_rules; i++) {
			assert(offset < total_len);
			scanf_fmts[i] = (char *)&scanf_fmts[nr_rules] + offset;
			offset += xsnprintf(scanf_fmts[i], total_len - offset,
					    ref_rev_parse_rules[i], 2, "%s") + 1;
		}
	}

	/* bail out if there are no rules */
	if (!nr_rules)
		return xstrdup(refname);

	/* buffer for scanf result, at most refname must fit */
	short_name = xstrdup(refname);

	/* skip first rule, it will always match */
	for (i = nr_rules - 1; i > 0 ; --i) {
		int j;
		int rules_to_fail = i;
		int short_name_len;

		if (1 != sscanf(refname, scanf_fmts[i], short_name))
			continue;

		short_name_len = strlen(short_name);

		/*
		 * in strict mode, all (except the matched one) rules
		 * must fail to resolve to a valid non-ambiguous ref
		 */
		if (strict)
			rules_to_fail = nr_rules;

		/*
		 * check if the short name resolves to a valid ref,
		 * but use only rules prior to the matched one
		 */
		for (j = 0; j < rules_to_fail; j++) {
			const char *rule = ref_rev_parse_rules[j];

			/* skip matched rule */
			if (i == j)
				continue;

			/*
			 * the short name is ambiguous, if it resolves
			 * (with this previous rule) to a valid ref
			 * read_ref() returns 0 on success
			 */
			strbuf_reset(&resolved_buf);
			strbuf_addf(&resolved_buf, rule,
				    short_name_len, short_name);
			if (refs_ref_exists(refs, resolved_buf.buf))
				break;
		}

		/*
		 * short name is non-ambiguous if all previous rules
		 * haven't resolved to a valid ref
		 */
		if (j == rules_to_fail) {
			strbuf_release(&resolved_buf);
			return short_name;
		}
	}

	strbuf_release(&resolved_buf);
	free(short_name);
	return xstrdup(refname);
}

char *shorten_unambiguous_ref(const char *refname, int strict)
{
	return refs_shorten_unambiguous_ref(get_main_ref_store(the_repository),
					    refname, strict);
}

static struct string_list *hide_refs;

int parse_hide_refs_config(const char *var, const char *value, const char *section)
{
	const char *key;
	if (!strcmp("transfer.hiderefs", var) ||
	    (!parse_config_key(var, section, NULL, NULL, &key) &&
	     !strcmp(key, "hiderefs"))) {
		char *ref;
		int len;

		if (!value)
			return config_error_nonbool(var);
		ref = xstrdup(value);
		len = strlen(ref);
		while (len && ref[len - 1] == '/')
			ref[--len] = '\0';
		if (!hide_refs) {
			hide_refs = xcalloc(1, sizeof(*hide_refs));
			hide_refs->strdup_strings = 1;
		}
		string_list_append(hide_refs, ref);
	}
	return 0;
}

int ref_is_hidden(const char *refname, const char *refname_full)
{
	int i;

	if (!hide_refs)
		return 0;
	for (i = hide_refs->nr - 1; i >= 0; i--) {
		const char *match = hide_refs->items[i].string;
		const char *subject;
		int neg = 0;
		const char *p;

		if (*match == '!') {
			neg = 1;
			match++;
		}

		if (*match == '^') {
			subject = refname_full;
			match++;
		} else {
			subject = refname;
		}

		/* refname can be NULL when namespaces are used. */
		if (subject &&
		    skip_prefix(subject, match, &p) &&
		    (!*p || *p == '/'))
			return !neg;
	}
	return 0;
}

const char *find_descendant_ref(const char *dirname,
				const struct string_list *extras,
				const struct string_list *skip)
{
	int pos;

	if (!extras)
		return NULL;

	/*
	 * Look at the place where dirname would be inserted into
	 * extras. If there is an entry at that position that starts
	 * with dirname (remember, dirname includes the trailing
	 * slash) and is not in skip, then we have a conflict.
	 */
	for (pos = string_list_find_insert_index(extras, dirname, 0);
	     pos < extras->nr; pos++) {
		const char *extra_refname = extras->items[pos].string;

		if (!starts_with(extra_refname, dirname))
			break;

		if (!skip || !string_list_has_string(skip, extra_refname))
			return extra_refname;
	}
	return NULL;
}

int refs_rename_ref_available(struct ref_store *refs,
			      const char *old_refname,
			      const char *new_refname)
{
	struct string_list skip = STRING_LIST_INIT_NODUP;
	struct strbuf err = STRBUF_INIT;
	int ok;

	string_list_insert(&skip, old_refname);
	ok = !refs_verify_refname_available(refs, new_refname,
					    NULL, &skip, &err);
	if (!ok)
		error("%s", err.buf);

	string_list_clear(&skip, 0);
	strbuf_release(&err);
	return ok;
}

int refs_head_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	struct object_id oid;
	int flag;

	if (!refs_read_ref_full(refs, "HEAD", RESOLVE_REF_READING,
				&oid, &flag))
		return fn("HEAD", &oid, flag, cb_data);

	return 0;
}

int head_ref(each_ref_fn fn, void *cb_data)
{
	return refs_head_ref(get_main_ref_store(the_repository), fn, cb_data);
}

struct ref_iterator *refs_ref_iterator_begin(
		struct ref_store *refs,
		const char *prefix, int trim, int flags)
{
	struct ref_iterator *iter;

	if (ref_paranoia < 0)
		ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
	if (ref_paranoia)
		flags |= DO_FOR_EACH_INCLUDE_BROKEN;

	iter = refs->be->iterator_begin(refs, prefix, flags);

	/*
	 * `iterator_begin()` already takes care of prefix, but we
	 * might need to do some trimming:
	 */
	if (trim)
		iter = prefix_ref_iterator_begin(iter, "", trim);

	/* Sanity check for subclasses: */
	if (!iter->ordered)
		BUG("reference iterator is not ordered");

	return iter;
}

/*
 * Call fn for each reference in the specified submodule for which the
 * refname begins with prefix. If trim is non-zero, then trim that
 * many characters off the beginning of each refname before passing
 * the refname to fn. flags can be DO_FOR_EACH_INCLUDE_BROKEN to
 * include broken references in the iteration. If fn ever returns a
 * non-zero value, stop the iteration and return that value;
 * otherwise, return 0.
 */
static int do_for_each_repo_ref(struct repository *r, const char *prefix,
				each_repo_ref_fn fn, int trim, int flags,
				void *cb_data)
{
	struct ref_iterator *iter;
	struct ref_store *refs = get_main_ref_store(r);

	if (!refs)
		return 0;

	iter = refs_ref_iterator_begin(refs, prefix, trim, flags);

	return do_for_each_repo_ref_iterator(r, iter, fn, cb_data);
}

struct do_for_each_ref_help {
	each_ref_fn *fn;
	void *cb_data;
};

static int do_for_each_ref_helper(struct repository *r,
				  const char *refname,
				  const struct object_id *oid,
				  int flags,
				  void *cb_data)
{
	struct do_for_each_ref_help *hp = cb_data;

	return hp->fn(refname, oid, flags, hp->cb_data);
}

static int do_for_each_ref(struct ref_store *refs, const char *prefix,
			   each_ref_fn fn, int trim, int flags, void *cb_data)
{
	struct ref_iterator *iter;
	struct do_for_each_ref_help hp = { fn, cb_data };

	if (!refs)
		return 0;

	iter = refs_ref_iterator_begin(refs, prefix, trim, flags);

	return do_for_each_repo_ref_iterator(the_repository, iter,
					do_for_each_ref_helper, &hp);
}

int refs_for_each_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref(refs, "", fn, 0, 0, cb_data);
}

int for_each_ref(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_ref(get_main_ref_store(the_repository), fn, cb_data);
}

int refs_for_each_ref_in(struct ref_store *refs, const char *prefix,
			 each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref(refs, prefix, fn, strlen(prefix), 0, cb_data);
}

int for_each_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
{
	return refs_for_each_ref_in(get_main_ref_store(the_repository), prefix, fn, cb_data);
}

int for_each_fullref_in(const char *prefix, each_ref_fn fn, void *cb_data, unsigned int broken)
{
	unsigned int flag = 0;

	if (broken)
		flag = DO_FOR_EACH_INCLUDE_BROKEN;
	return do_for_each_ref(get_main_ref_store(the_repository),
			       prefix, fn, 0, flag, cb_data);
}

int refs_for_each_fullref_in(struct ref_store *refs, const char *prefix,
			     each_ref_fn fn, void *cb_data,
			     unsigned int broken)
{
	unsigned int flag = 0;

	if (broken)
		flag = DO_FOR_EACH_INCLUDE_BROKEN;
	return do_for_each_ref(refs, prefix, fn, 0, flag, cb_data);
}

int for_each_replace_ref(struct repository *r, each_repo_ref_fn fn, void *cb_data)
{
	return do_for_each_repo_ref(r, git_replace_ref_base, fn,
				    strlen(git_replace_ref_base),
				    DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
}

int for_each_namespaced_ref(each_ref_fn fn, void *cb_data)
{
	struct strbuf buf = STRBUF_INIT;
	int ret;
	strbuf_addf(&buf, "%srefs/", get_git_namespace());
	ret = do_for_each_ref(get_main_ref_store(the_repository),
			      buf.buf, fn, 0, 0, cb_data);
	strbuf_release(&buf);
	return ret;
}

int refs_for_each_rawref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref(refs, "", fn, 0,
			       DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
}

int for_each_rawref(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_rawref(get_main_ref_store(the_repository), fn, cb_data);
}

int refs_read_raw_ref(struct ref_store *ref_store,
		      const char *refname, struct object_id *oid,
		      struct strbuf *referent, unsigned int *type)
{
	return ref_store->be->read_raw_ref(ref_store, refname, oid, referent, type);
}

/* This function needs to return a meaningful errno on failure */
const char *refs_resolve_ref_unsafe(struct ref_store *refs,
				    const char *refname,
				    int resolve_flags,
				    struct object_id *oid, int *flags)
{
	static struct strbuf sb_refname = STRBUF_INIT;
	struct object_id unused_oid;
	int unused_flags;
	int symref_count;

	if (!oid)
		oid = &unused_oid;
	if (!flags)
		flags = &unused_flags;

	*flags = 0;

	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
		if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
		    !refname_is_safe(refname)) {
			errno = EINVAL;
			return NULL;
		}

		/*
		 * dwim_ref() uses REF_ISBROKEN to distinguish between
		 * missing refs and refs that were present but invalid,
		 * to complain about the latter to stderr.
		 *
		 * We don't know whether the ref exists, so don't set
		 * REF_ISBROKEN yet.
		 */
		*flags |= REF_BAD_NAME;
	}

	for (symref_count = 0; symref_count < SYMREF_MAXDEPTH; symref_count++) {
		unsigned int read_flags = 0;

		if (refs_read_raw_ref(refs, refname,
				      oid, &sb_refname, &read_flags)) {
			*flags |= read_flags;

			/* In reading mode, refs must eventually resolve */
			if (resolve_flags & RESOLVE_REF_READING)
				return NULL;

			/*
			 * Otherwise a missing ref is OK. But the files backend
			 * may show errors besides ENOENT if there are
			 * similarly-named refs.
			 */
			if (errno != ENOENT &&
			    errno != EISDIR &&
			    errno != ENOTDIR)
				return NULL;

			oidclr(oid);
			if (*flags & REF_BAD_NAME)
				*flags |= REF_ISBROKEN;
			return refname;
		}

		*flags |= read_flags;

		if (!(read_flags & REF_ISSYMREF)) {
			if (*flags & REF_BAD_NAME) {
				oidclr(oid);
				*flags |= REF_ISBROKEN;
			}
			return refname;
		}

		refname = sb_refname.buf;
		if (resolve_flags & RESOLVE_REF_NO_RECURSE) {
			oidclr(oid);
			return refname;
		}
		if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
			if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
			    !refname_is_safe(refname)) {
				errno = EINVAL;
				return NULL;
			}

			*flags |= REF_ISBROKEN | REF_BAD_NAME;
		}
	}

	errno = ELOOP;
	return NULL;
}

/* backend functions */
int refs_init_db(struct strbuf *err)
{
	struct ref_store *refs = get_main_ref_store(the_repository);

	return refs->be->init_db(refs, err);
}

const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
			       struct object_id *oid, int *flags)
{
	return refs_resolve_ref_unsafe(get_main_ref_store(the_repository), refname,
				       resolve_flags, oid, flags);
}

int resolve_gitlink_ref(const char *submodule, const char *refname,
			struct object_id *oid)
{
	struct ref_store *refs;
	int flags;

	refs = get_submodule_ref_store(submodule);

	if (!refs)
		return -1;

	if (!refs_resolve_ref_unsafe(refs, refname, 0, oid, &flags) ||
	    is_null_oid(oid))
		return -1;
	return 0;
}

struct ref_store_hash_entry
{
	struct hashmap_entry ent;

	struct ref_store *refs;

	/* NUL-terminated identifier of the ref store: */
	char name[FLEX_ARRAY];
};

static int ref_store_hash_cmp(const void *unused_cmp_data,
			      const struct hashmap_entry *eptr,
			      const struct hashmap_entry *entry_or_key,
			      const void *keydata)
{
	const struct ref_store_hash_entry *e1, *e2;
	const char *name;

	e1 = container_of(eptr, const struct ref_store_hash_entry, ent);
	e2 = container_of(entry_or_key, const struct ref_store_hash_entry, ent);
	name = keydata ? keydata : e2->name;

	return strcmp(e1->name, name);
}

static struct ref_store_hash_entry *alloc_ref_store_hash_entry(
		const char *name, struct ref_store *refs)
{
	struct ref_store_hash_entry *entry;

	FLEX_ALLOC_STR(entry, name, name);
	hashmap_entry_init(&entry->ent, strhash(name));
	entry->refs = refs;
	return entry;
}

/* A hashmap of ref_stores, stored by submodule name: */
static struct hashmap submodule_ref_stores;

/* A hashmap of ref_stores, stored by worktree id: */
static struct hashmap worktree_ref_stores;

/*
 * Look up a ref store by name. If that ref_store hasn't been
 * registered yet, return NULL.
 */
static struct ref_store *lookup_ref_store_map(struct hashmap *map,
					      const char *name)
{
	struct ref_store_hash_entry *entry;
	unsigned int hash;

	if (!map->tablesize)
		/* It's initialized on demand in register_ref_store(). */
		return NULL;

	hash = strhash(name);
	entry = hashmap_get_entry_from_hash(map, hash, name,
					struct ref_store_hash_entry, ent);
	return entry ? entry->refs : NULL;
}

/*
 * Create, record, and return a ref_store instance for the specified
 * gitdir.
 */
static struct ref_store *ref_store_init(const char *gitdir,
					unsigned int flags)
{
	const char *be_name = "files";
	struct ref_storage_be *be = find_ref_storage_backend(be_name);
	struct ref_store *refs;

	if (!be)
		BUG("reference backend %s is unknown", be_name);

	refs = be->init(gitdir, flags);
	return refs;
}

struct ref_store *get_main_ref_store(struct repository *r)
{
	if (r->refs_private)
		return r->refs_private;

	if (!r->gitdir)
		BUG("attempting to get main_ref_store outside of repository");

	r->refs_private = ref_store_init(r->gitdir, REF_STORE_ALL_CAPS);
	return r->refs_private;
}

/*
 * Associate a ref store with a name. It is a fatal error to call this
 * function twice for the same name.
 */
static void register_ref_store_map(struct hashmap *map,
				   const char *type,
				   struct ref_store *refs,
				   const char *name)
{
	struct ref_store_hash_entry *entry;

	if (!map->tablesize)
		hashmap_init(map, ref_store_hash_cmp, NULL, 0);

	entry = alloc_ref_store_hash_entry(name, refs);
	if (hashmap_put(map, &entry->ent))
		BUG("%s ref_store '%s' initialized twice", type, name);
}

struct ref_store *get_submodule_ref_store(const char *submodule)
{
	struct strbuf submodule_sb = STRBUF_INIT;
	struct ref_store *refs;
	char *to_free = NULL;
	size_t len;

	if (!submodule)
		return NULL;

	len = strlen(submodule);
	while (len && is_dir_sep(submodule[len - 1]))
		len--;
	if (!len)
		return NULL;

	if (submodule[len])
		/* We need to strip off one or more trailing slashes */
		submodule = to_free = xmemdupz(submodule, len);

	refs = lookup_ref_store_map(&submodule_ref_stores, submodule);
	if (refs)
		goto done;

	strbuf_addstr(&submodule_sb, submodule);
	if (!is_nonbare_repository_dir(&submodule_sb))
		goto done;

	if (submodule_to_gitdir(&submodule_sb, submodule))
		goto done;

	/* assume that add_submodule_odb() has been called */
	refs = ref_store_init(submodule_sb.buf,
			      REF_STORE_READ | REF_STORE_ODB);
	register_ref_store_map(&submodule_ref_stores, "submodule",
			       refs, submodule);

done:
	strbuf_release(&submodule_sb);
	free(to_free);

	return refs;
}

struct ref_store *get_worktree_ref_store(const struct worktree *wt)
{
	struct ref_store *refs;
	const char *id;

	if (wt->is_current)
		return get_main_ref_store(the_repository);

	id = wt->id ? wt->id : "/";
	refs = lookup_ref_store_map(&worktree_ref_stores, id);
	if (refs)
		return refs;

	if (wt->id)
		refs = ref_store_init(git_common_path("worktrees/%s", wt->id),
				      REF_STORE_ALL_CAPS);
	else
		refs = ref_store_init(get_git_common_dir(),
				      REF_STORE_ALL_CAPS);

	if (refs)
		register_ref_store_map(&worktree_ref_stores, "worktree",
				       refs, id);
	return refs;
}

void base_ref_store_init(struct ref_store *refs,
			 const struct ref_storage_be *be)
{
	refs->be = be;
}

/* backend functions */
int refs_pack_refs(struct ref_store *refs, unsigned int flags)
{
	return refs->be->pack_refs(refs, flags);
}

int refs_peel_ref(struct ref_store *refs, const char *refname,
		  struct object_id *oid)
{
	int flag;
	struct object_id base;

	if (current_ref_iter && current_ref_iter->refname == refname) {
		struct object_id peeled;

		if (ref_iterator_peel(current_ref_iter, &peeled))
			return -1;
		oidcpy(oid, &peeled);
		return 0;
	}

	if (refs_read_ref_full(refs, refname,
			       RESOLVE_REF_READING, &base, &flag))
		return -1;

	return peel_object(&base, oid);
}

int peel_ref(const char *refname, struct object_id *oid)
{
	return refs_peel_ref(get_main_ref_store(the_repository), refname, oid);
}

int refs_create_symref(struct ref_store *refs,
		       const char *ref_target,
		       const char *refs_heads_master,
		       const char *logmsg)
{
	return refs->be->create_symref(refs, ref_target,
				       refs_heads_master,
				       logmsg);
}

int create_symref(const char *ref_target, const char *refs_heads_master,
		  const char *logmsg)
{
	return refs_create_symref(get_main_ref_store(the_repository), ref_target,
				  refs_heads_master, logmsg);
}

int ref_update_reject_duplicates(struct string_list *refnames,
				 struct strbuf *err)
{
	size_t i, n = refnames->nr;

	assert(err);

	for (i = 1; i < n; i++) {
		int cmp = strcmp(refnames->items[i - 1].string,
				 refnames->items[i].string);

		if (!cmp) {
			strbuf_addf(err,
				    _("multiple updates for ref '%s' not allowed"),
				    refnames->items[i].string);
			return 1;
		} else if (cmp > 0) {
			BUG("ref_update_reject_duplicates() received unsorted list");
		}
	}
	return 0;
}

static const char hook_not_found;
static const char *hook;

static int run_transaction_hook(struct ref_transaction *transaction,
				const char *state)
{
	struct child_process proc = CHILD_PROCESS_INIT;
	struct strbuf buf = STRBUF_INIT;
	int ret = 0, i;

	if (hook == &hook_not_found)
		return ret;
	if (!hook)
		hook = find_hook("reference-transaction");
	if (!hook) {
		hook = &hook_not_found;
		return ret;
	}

	argv_array_pushl(&proc.args, hook, state, NULL);
	proc.in = -1;
	proc.stdout_to_stderr = 1;
	proc.trace2_hook_name = "reference-transaction";

	ret = start_command(&proc);
	if (ret)
		return ret;

	sigchain_push(SIGPIPE, SIG_IGN);

	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];

		strbuf_reset(&buf);
		strbuf_addf(&buf, "%s %s %s\n",
			    oid_to_hex(&update->old_oid),
			    oid_to_hex(&update->new_oid),
			    update->refname);

		if (write_in_full(proc.in, buf.buf, buf.len) < 0) {
			if (errno != EPIPE)
				ret = -1;
			break;
		}
	}

	close(proc.in);
	sigchain_pop(SIGPIPE);
	strbuf_release(&buf);

	ret |= finish_command(&proc);
	return ret;
}

int ref_transaction_prepare(struct ref_transaction *transaction,
			    struct strbuf *err)
{
	struct ref_store *refs = transaction->ref_store;
	int ret;

	switch (transaction->state) {
	case REF_TRANSACTION_OPEN:
		/* Good. */
		break;
	case REF_TRANSACTION_PREPARED:
		BUG("prepare called twice on reference transaction");
		break;
	case REF_TRANSACTION_CLOSED:
		BUG("prepare called on a closed reference transaction");
		break;
	default:
		BUG("unexpected reference transaction state");
		break;
	}

	if (getenv(GIT_QUARANTINE_ENVIRONMENT)) {
		strbuf_addstr(err,
			      _("ref updates forbidden inside quarantine environment"));
		return -1;
	}

	ret = refs->be->transaction_prepare(refs, transaction, err);
	if (ret)
		return ret;

	ret = run_transaction_hook(transaction, "prepared");
	if (ret) {
		ref_transaction_abort(transaction, err);
		die(_("ref updates aborted by hook"));
	}

	return 0;
}

int ref_transaction_abort(struct ref_transaction *transaction,
			  struct strbuf *err)
{
	struct ref_store *refs = transaction->ref_store;
	int ret = 0;

	switch (transaction->state) {
	case REF_TRANSACTION_OPEN:
		/* No need to abort explicitly. */
		break;
	case REF_TRANSACTION_PREPARED:
		ret = refs->be->transaction_abort(refs, transaction, err);
		break;
	case REF_TRANSACTION_CLOSED:
		BUG("abort called on a closed reference transaction");
		break;
	default:
		BUG("unexpected reference transaction state");
		break;
	}

	run_transaction_hook(transaction, "aborted");

	ref_transaction_free(transaction);
	return ret;
}

int ref_transaction_commit(struct ref_transaction *transaction,
			   struct strbuf *err)
{
	struct ref_store *refs = transaction->ref_store;
	int ret;

	switch (transaction->state) {
	case REF_TRANSACTION_OPEN:
		/* Need to prepare first. */
		ret = ref_transaction_prepare(transaction, err);
		if (ret)
			return ret;
		break;
	case REF_TRANSACTION_PREPARED:
		/* Fall through to finish. */
		break;
	case REF_TRANSACTION_CLOSED:
		BUG("commit called on a closed reference transaction");
		break;
	default:
		BUG("unexpected reference transaction state");
		break;
	}

	ret = refs->be->transaction_finish(refs, transaction, err);
	if (!ret)
		run_transaction_hook(transaction, "committed");
	return ret;
}

int refs_verify_refname_available(struct ref_store *refs,
				  const char *refname,
				  const struct string_list *extras,
				  const struct string_list *skip,
				  struct strbuf *err)
{
	const char *slash;
	const char *extra_refname;
	struct strbuf dirname = STRBUF_INIT;
	struct strbuf referent = STRBUF_INIT;
	struct object_id oid;
	unsigned int type;
	struct ref_iterator *iter;
	int ok;
	int ret = -1;

	/*
	 * For the sake of comments in this function, suppose that
	 * refname is "refs/foo/bar".
	 */

	assert(err);

	strbuf_grow(&dirname, strlen(refname) + 1);
	for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
		/* Expand dirname to the new prefix, not including the trailing slash: */
		strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);

		/*
		 * We are still at a leading dir of the refname (e.g.,
		 * "refs/foo"; if there is a reference with that name,
		 * it is a conflict, *unless* it is in skip.
		 */
		if (skip && string_list_has_string(skip, dirname.buf))
			continue;

		if (!refs_read_raw_ref(refs, dirname.buf, &oid, &referent, &type)) {
			strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
				    dirname.buf, refname);
			goto cleanup;
		}

		if (extras && string_list_has_string(extras, dirname.buf)) {
			strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
				    refname, dirname.buf);
			goto cleanup;
		}
	}

	/*
	 * We are at the leaf of our refname (e.g., "refs/foo/bar").
	 * There is no point in searching for a reference with that
	 * name, because a refname isn't considered to conflict with
	 * itself. But we still need to check for references whose
	 * names are in the "refs/foo/bar/" namespace, because they
	 * *do* conflict.
	 */
	strbuf_addstr(&dirname, refname + dirname.len);
	strbuf_addch(&dirname, '/');

	iter = refs_ref_iterator_begin(refs, dirname.buf, 0,
				       DO_FOR_EACH_INCLUDE_BROKEN);
	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
		if (skip &&
		    string_list_has_string(skip, iter->refname))
			continue;

		strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
			    iter->refname, refname);
		ref_iterator_abort(iter);
		goto cleanup;
	}

	if (ok != ITER_DONE)
		BUG("error while iterating over references");

	extra_refname = find_descendant_ref(dirname.buf, extras, skip);
	if (extra_refname)
		strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
			    refname, extra_refname);
	else
		ret = 0;

cleanup:
	strbuf_release(&referent);
	strbuf_release(&dirname);
	return ret;
}

int refs_for_each_reflog(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
	struct ref_iterator *iter;
	struct do_for_each_ref_help hp = { fn, cb_data };

	iter = refs->be->reflog_iterator_begin(refs);

	return do_for_each_repo_ref_iterator(the_repository, iter,
					     do_for_each_ref_helper, &hp);
}

int for_each_reflog(each_ref_fn fn, void *cb_data)
{
	return refs_for_each_reflog(get_main_ref_store(the_repository), fn, cb_data);
}

int refs_for_each_reflog_ent_reverse(struct ref_store *refs,
				     const char *refname,
				     each_reflog_ent_fn fn,
				     void *cb_data)
{
	return refs->be->for_each_reflog_ent_reverse(refs, refname,
						     fn, cb_data);
}

int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn,
				void *cb_data)
{
	return refs_for_each_reflog_ent_reverse(get_main_ref_store(the_repository),
						refname, fn, cb_data);
}

int refs_for_each_reflog_ent(struct ref_store *refs, const char *refname,
			     each_reflog_ent_fn fn, void *cb_data)
{
	return refs->be->for_each_reflog_ent(refs, refname, fn, cb_data);
}

int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn,
			void *cb_data)
{
	return refs_for_each_reflog_ent(get_main_ref_store(the_repository), refname,
					fn, cb_data);
}

int refs_reflog_exists(struct ref_store *refs, const char *refname)
{
	return refs->be->reflog_exists(refs, refname);
}

int reflog_exists(const char *refname)
{
	return refs_reflog_exists(get_main_ref_store(the_repository), refname);
}

int refs_create_reflog(struct ref_store *refs, const char *refname,
		       int force_create, struct strbuf *err)
{
	return refs->be->create_reflog(refs, refname, force_create, err);
}

int safe_create_reflog(const char *refname, int force_create,
		       struct strbuf *err)
{
	return refs_create_reflog(get_main_ref_store(the_repository), refname,
				  force_create, err);
}

int refs_delete_reflog(struct ref_store *refs, const char *refname)
{
	return refs->be->delete_reflog(refs, refname);
}

int delete_reflog(const char *refname)
{
	return refs_delete_reflog(get_main_ref_store(the_repository), refname);
}

int refs_reflog_expire(struct ref_store *refs,
		       const char *refname, const struct object_id *oid,
		       unsigned int flags,
		       reflog_expiry_prepare_fn prepare_fn,
		       reflog_expiry_should_prune_fn should_prune_fn,
		       reflog_expiry_cleanup_fn cleanup_fn,
		       void *policy_cb_data)
{
	return refs->be->reflog_expire(refs, refname, oid, flags,
				       prepare_fn, should_prune_fn,
				       cleanup_fn, policy_cb_data);
}

int reflog_expire(const char *refname, const struct object_id *oid,
		  unsigned int flags,
		  reflog_expiry_prepare_fn prepare_fn,
		  reflog_expiry_should_prune_fn should_prune_fn,
		  reflog_expiry_cleanup_fn cleanup_fn,
		  void *policy_cb_data)
{
	return refs_reflog_expire(get_main_ref_store(the_repository),
				  refname, oid, flags,
				  prepare_fn, should_prune_fn,
				  cleanup_fn, policy_cb_data);
}

int initial_ref_transaction_commit(struct ref_transaction *transaction,
				   struct strbuf *err)
{
	struct ref_store *refs = transaction->ref_store;

	return refs->be->initial_transaction_commit(refs, transaction, err);
}

int refs_delete_refs(struct ref_store *refs, const char *msg,
		     struct string_list *refnames, unsigned int flags)
{
	return refs->be->delete_refs(refs, msg, refnames, flags);
}

int delete_refs(const char *msg, struct string_list *refnames,
		unsigned int flags)
{
	return refs_delete_refs(get_main_ref_store(the_repository), msg, refnames, flags);
}

int refs_rename_ref(struct ref_store *refs, const char *oldref,
		    const char *newref, const char *logmsg)
{
	return refs->be->rename_ref(refs, oldref, newref, logmsg);
}

int rename_ref(const char *oldref, const char *newref, const char *logmsg)
{
	return refs_rename_ref(get_main_ref_store(the_repository), oldref, newref, logmsg);
}

int refs_copy_existing_ref(struct ref_store *refs, const char *oldref,
		    const char *newref, const char *logmsg)
{
	return refs->be->copy_ref(refs, oldref, newref, logmsg);
}

int copy_existing_ref(const char *oldref, const char *newref, const char *logmsg)
{
	return refs_copy_existing_ref(get_main_ref_store(the_repository), oldref, newref, logmsg);
}