Merge branch 'ab/refs-errno-cleanup' into next

The "remainder" of hn/refs-errno-cleanup topic.

* ab/refs-errno-cleanup: (21 commits)
  refs API: post-migration API renaming [2/2]
  refs API: post-migration API renaming [1/2]
  refs API: don't expose "errno" in run_transaction_hook()
  refs API: make expand_ref() & repo_dwim_log() not set errno
  refs API: make resolve_ref_unsafe() not set errno
  refs API: make refs_ref_exists() not set errno
  refs API: make refs_resolve_refdup() not set errno
  refs tests: ignore ignore errno in test-ref-store helper
  refs API: ignore errno in worktree.c's find_shared_symref()
  refs API: ignore errno in worktree.c's add_head_info()
  refs API: make files_copy_or_rename_ref() et al not set errno
  refs API: make loose_fill_ref_dir() not set errno
  refs API: make resolve_gitlink_ref() not set errno
  refs API: remove refs_read_ref_full() wrapper
  refs/files: remove "name exist?" check in lock_ref_oid_basic()
  reflog tests: add --updateref tests
  refs API: make refs_rename_ref_available() static
  refs API: make parse_loose_ref_contents() not set errno
  refs API: make refs_read_raw_ref() not set errno
  refs API: add a version of refs_resolve_ref_unsafe() with "errno"
  ...

10 files changed, 294 insertions, 143 deletions

diff --git a/refs.c b/refs.c
index 27ec7d1fc6..b3e4663aeb 100644
--- a/refs.c
+++ b/refs.c
@@ -269,9 +269,10 @@ char *refs_resolve_refdup(struct ref_store *refs,
 			  struct object_id *oid, int *flags)
 {
 	const char *result;
+	int ignore_errno;
 
 	result = refs_resolve_ref_unsafe(refs, refname, resolve_flags,
-					 oid, flags);
+					 oid, flags, &ignore_errno);
 	return xstrdup_or_null(result);
 }
 
@@ -291,20 +292,17 @@ struct ref_filter {
 	void *cb_data;
 };
 
-int refs_read_ref_full(struct ref_store *refs, const char *refname,
-		       int resolve_flags, struct object_id *oid, int *flags)
+int read_ref_full(const char *refname, int resolve_flags, struct object_id *oid, int *flags)
 {
-	if (refs_resolve_ref_unsafe(refs, refname, resolve_flags, oid, flags))
+	int ignore_errno;
+	struct ref_store *refs = get_main_ref_store(the_repository);
+
+	if (refs_resolve_ref_unsafe(refs, refname, resolve_flags,
+				    oid, flags, &ignore_errno))
 		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);
@@ -312,7 +310,9 @@ int read_ref(const char *refname, struct object_id *oid)
 
 int refs_ref_exists(struct ref_store *refs, const char *refname)
 {
-	return !!refs_resolve_ref_unsafe(refs, refname, RESOLVE_REF_READING, NULL, NULL);
+	int ignore_errno;
+	return !!refs_resolve_ref_unsafe(refs, refname, RESOLVE_REF_READING,
+					 NULL, NULL, &ignore_errno);
 }
 
 int ref_exists(const char *refname)
@@ -655,13 +655,16 @@ int expand_ref(struct repository *repo, const char *str, int len,
 		struct object_id oid_from_ref;
 		struct object_id *this_result;
 		int flag;
+		struct ref_store *refs = get_main_ref_store(repo);
+		int ignore_errno;
 
 		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);
+		r = refs_resolve_ref_unsafe(refs, fullref.buf,
+					    RESOLVE_REF_READING,
+					    this_result, &flag,
+					    &ignore_errno);
 		if (r) {
 			if (!refs_found++)
 				*ref = xstrdup(r);
@@ -690,12 +693,14 @@ int repo_dwim_log(struct repository *r, const char *str, int len,
 	for (p = ref_rev_parse_rules; *p; p++) {
 		struct object_id hash;
 		const char *ref, *it;
+		int ignore_errno;
 
 		strbuf_reset(&path);
 		strbuf_addf(&path, *p, len, str);
 		ref = refs_resolve_ref_unsafe(refs, path.buf,
 					      RESOLVE_REF_READING,
-					      oid ? &hash : NULL, NULL);
+					      oid ? &hash : NULL, NULL,
+					      &ignore_errno);
 		if (!ref)
 			continue;
 		if (refs_reflog_exists(refs, path.buf))
@@ -1373,32 +1378,14 @@ const char *find_descendant_ref(const char *dirname,
 	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;
+	int ignore_errno;
 
-	if (!refs_read_ref_full(refs, "HEAD", RESOLVE_REF_READING,
-				&oid, &flag))
+	if (refs_resolve_ref_unsafe(refs, "HEAD", RESOLVE_REF_READING,
+				    &oid, &flag, &ignore_errno))
 		return fn("HEAD", &oid, flag, cb_data);
 
 	return 0;
@@ -1649,7 +1636,8 @@ int for_each_fullref_in_prefixes(const char *namespace,
 
 static int refs_read_special_head(struct ref_store *ref_store,
 				  const char *refname, struct object_id *oid,
-				  struct strbuf *referent, unsigned int *type)
+				  struct strbuf *referent, unsigned int *type,
+				  int *failure_errno)
 {
 	struct strbuf full_path = STRBUF_INIT;
 	struct strbuf content = STRBUF_INIT;
@@ -1659,7 +1647,8 @@ static int refs_read_special_head(struct ref_store *ref_store,
 	if (strbuf_read_file(&content, full_path.buf, 0) < 0)
 		goto done;
 
-	result = parse_loose_ref_contents(content.buf, oid, referent, type);
+	result = parse_loose_ref_contents(content.buf, oid, referent, type,
+					  failure_errno);
 
 done:
 	strbuf_release(&full_path);
@@ -1667,30 +1656,33 @@ done:
 	return result;
 }
 
-int refs_read_raw_ref(struct ref_store *ref_store,
-		      const char *refname, struct object_id *oid,
-		      struct strbuf *referent, unsigned int *type)
+int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
+		      struct object_id *oid, struct strbuf *referent,
+		      unsigned int *type, int *failure_errno)
 {
+	assert(failure_errno);
 	if (!strcmp(refname, "FETCH_HEAD") || !strcmp(refname, "MERGE_HEAD")) {
 		return refs_read_special_head(ref_store, refname, oid, referent,
-					      type);
+					      type, failure_errno);
 	}
 
 	return ref_store->be->read_raw_ref(ref_store, refname, oid, referent,
-					   type, &errno);
+					   type, failure_errno);
 }
 
-/* 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)
+				    struct object_id *oid,
+				    int *flags, int *failure_errno)
 {
 	static struct strbuf sb_refname = STRBUF_INIT;
 	struct object_id unused_oid;
 	int unused_flags;
 	int symref_count;
 
+	assert(failure_errno);
+
 	if (!oid)
 		oid = &unused_oid;
 	if (!flags)
@@ -1701,7 +1693,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 		if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
 		    !refname_is_safe(refname)) {
-			errno = EINVAL;
+			*failure_errno = EINVAL;
 			return NULL;
 		}
 
@@ -1719,9 +1711,11 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 	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)) {
+		if (refs_read_raw_ref(refs, refname, oid, &sb_refname,
+				      &read_flags, failure_errno)) {
 			*flags |= read_flags;
+			if (errno)
+				*failure_errno = errno;
 
 			/* In reading mode, refs must eventually resolve */
 			if (resolve_flags & RESOLVE_REF_READING)
@@ -1732,9 +1726,9 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 			 * may show errors besides ENOENT if there are
 			 * similarly-named refs.
 			 */
-			if (errno != ENOENT &&
-			    errno != EISDIR &&
-			    errno != ENOTDIR)
+			if (*failure_errno != ENOENT &&
+			    *failure_errno != EISDIR &&
+			    *failure_errno != ENOTDIR)
 				return NULL;
 
 			oidclr(oid);
@@ -1761,7 +1755,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 		if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 			if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
 			    !refname_is_safe(refname)) {
-				errno = EINVAL;
+				*failure_errno = EINVAL;
 				return NULL;
 			}
 
@@ -1769,7 +1763,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 		}
 	}
 
-	errno = ELOOP;
+	*failure_errno = ELOOP;
 	return NULL;
 }
 
@@ -1784,8 +1778,10 @@ int refs_init_db(struct strbuf *err)
 const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 			       struct object_id *oid, int *flags)
 {
+	int ignore_errno;
+
 	return refs_resolve_ref_unsafe(get_main_ref_store(the_repository), refname,
-				       resolve_flags, oid, flags);
+				       resolve_flags, oid, flags, &ignore_errno);
 }
 
 int resolve_gitlink_ref(const char *submodule, const char *refname,
@@ -1793,14 +1789,15 @@ int resolve_gitlink_ref(const char *submodule, const char *refname,
 {
 	struct ref_store *refs;
 	int flags;
+	int ignore_errno;
 
 	refs = get_submodule_ref_store(submodule);
 
 	if (!refs)
 		return -1;
 
-	if (!refs_resolve_ref_unsafe(refs, refname, 0, oid, &flags) ||
-	    is_null_oid(oid))
+	if (!refs_resolve_ref_unsafe(refs, refname, 0, oid, &flags,
+				     &ignore_errno) || is_null_oid(oid))
 		return -1;
 	return 0;
 }
@@ -2102,8 +2099,11 @@ static int run_transaction_hook(struct ref_transaction *transaction,
 			    update->refname);
 
 		if (write_in_full(proc.in, buf.buf, buf.len) < 0) {
-			if (errno != EPIPE)
+			if (errno != EPIPE) {
+				/* Don't leak errno outside this API */
+				errno = 0;
 				ret = -1;
+			}
 			break;
 		}
 	}
@@ -2238,6 +2238,13 @@ int refs_verify_refname_available(struct ref_store *refs,
 
 	strbuf_grow(&dirname, strlen(refname) + 1);
 	for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+		/*
+		 * Just saying "Is a directory" when we e.g. can't
+		 * lock some multi-level ref isn't very informative,
+		 * the user won't be told *what* is a directory, so
+		 * let's not use strerror() below.
+		 */
+		int ignore_errno;
 		/* Expand dirname to the new prefix, not including the trailing slash: */
 		strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
 
@@ -2249,7 +2256,8 @@ int refs_verify_refname_available(struct ref_store *refs,
 		if (skip && string_list_has_string(skip, dirname.buf))
 			continue;
 
-		if (!refs_read_raw_ref(refs, dirname.buf, &oid, &referent, &type)) {
+		if (!refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
+				       &type, &ignore_errno)) {
 			strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
 				    dirname.buf, refname);
 			goto cleanup;
diff --git a/refs.h b/refs.h
index d5099d4984..45c34e99e3 100644
--- a/refs.h
+++ b/refs.h
@@ -58,6 +58,11 @@ struct worktree;
  * resolved. The function returns NULL for such ref names.
  * Caps and underscores refers to the special refs, such as HEAD,
  * FETCH_HEAD and friends, that all live outside of the refs/ directory.
+ *
+ * Callers should not inspect "errno" on failure, but rather pass in a
+ * "failure_errno" parameter, on failure the "errno" will indicate the
+ * type of failure encountered, but not necessarily one that came from
+ * a syscall. We might have faked it up.
  */
 #define RESOLVE_REF_READING 0x01
 #define RESOLVE_REF_NO_RECURSE 0x02
@@ -67,7 +72,8 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 				    const char *refname,
 				    int resolve_flags,
 				    struct object_id *oid,
-				    int *flags);
+				    int *flags, int *failure_errno);
+
 const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 			       struct object_id *oid, int *flags);
 
@@ -77,8 +83,6 @@ char *refs_resolve_refdup(struct ref_store *refs,
 char *resolve_refdup(const char *refname, int resolve_flags,
 		     struct object_id *oid, int *flags);
 
-int refs_read_ref_full(struct ref_store *refs, const char *refname,
-		       int resolve_flags, struct object_id *oid, int *flags);
 int read_ref_full(const char *refname, int resolve_flags,
 		  struct object_id *oid, int *flags);
 int read_ref(const char *refname, struct object_id *oid);
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 151b0056fe..4b14f30d48 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -282,10 +282,11 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 					 create_dir_entry(dir->cache, refname.buf,
 							  refname.len));
 		} else {
+			int ignore_errno;
 			if (!refs_resolve_ref_unsafe(&refs->base,
 						     refname.buf,
 						     RESOLVE_REF_READING,
-						     &oid, &flag)) {
+						     &oid, &flag, &ignore_errno)) {
 				oidclr(&oid);
 				flag |= REF_ISBROKEN;
 			} else if (is_null_oid(&oid)) {
@@ -357,6 +358,7 @@ static int files_read_raw_ref(struct ref_store *ref_store, const char *refname,
 	int fd;
 	int ret = -1;
 	int remaining_retries = 3;
+	int myerr = 0;
 
 	*type = 0;
 	strbuf_reset(&sb_path);
@@ -383,11 +385,14 @@ stat_ref:
 		goto out;
 
 	if (lstat(path, &st) < 0) {
-		if (errno != ENOENT)
+		int ignore_errno;
+		myerr = errno;
+		errno = 0;
+		if (myerr != ENOENT)
 			goto out;
-		if (refs_read_raw_ref(refs->packed_ref_store, refname,
-				      oid, referent, type)) {
-			errno = ENOENT;
+		if (refs_read_raw_ref(refs->packed_ref_store, refname, oid,
+				      referent, type, &ignore_errno)) {
+			myerr = ENOENT;
 			goto out;
 		}
 		ret = 0;
@@ -398,7 +403,9 @@ stat_ref:
 	if (S_ISLNK(st.st_mode)) {
 		strbuf_reset(&sb_contents);
 		if (strbuf_readlink(&sb_contents, path, st.st_size) < 0) {
-			if (errno == ENOENT || errno == EINVAL)
+			myerr = errno;
+			errno = 0;
+			if (myerr == ENOENT || myerr == EINVAL)
 				/* inconsistent with lstat; retry */
 				goto stat_ref;
 			else
@@ -420,14 +427,15 @@ stat_ref:
 
 	/* Is it a directory? */
 	if (S_ISDIR(st.st_mode)) {
+		int ignore_errno;
 		/*
 		 * Even though there is a directory where the loose
 		 * ref is supposed to be, there could still be a
 		 * packed ref:
 		 */
-		if (refs_read_raw_ref(refs->packed_ref_store, refname,
-				      oid, referent, type)) {
-			errno = EISDIR;
+		if (refs_read_raw_ref(refs->packed_ref_store, refname, oid,
+				      referent, type, &ignore_errno)) {
+			myerr = EISDIR;
 			goto out;
 		}
 		ret = 0;
@@ -440,7 +448,8 @@ stat_ref:
 	 */
 	fd = open(path, O_RDONLY);
 	if (fd < 0) {
-		if (errno == ENOENT && !S_ISLNK(st.st_mode))
+		myerr = errno;
+		if (myerr == ENOENT && !S_ISLNK(st.st_mode))
 			/* inconsistent with lstat; retry */
 			goto stat_ref;
 		else
@@ -448,26 +457,29 @@ stat_ref:
 	}
 	strbuf_reset(&sb_contents);
 	if (strbuf_read(&sb_contents, fd, 256) < 0) {
-		int save_errno = errno;
+		myerr = errno;
 		close(fd);
-		errno = save_errno;
 		goto out;
 	}
 	close(fd);
 	strbuf_rtrim(&sb_contents);
 	buf = sb_contents.buf;
 
-	ret = parse_loose_ref_contents(buf, oid, referent, type);
+	ret = parse_loose_ref_contents(buf, oid, referent, type, &myerr);
 
 out:
-	*failure_errno = errno;
+	if (ret && !myerr)
+		BUG("returning non-zero %d, should have set myerr!", ret);
+	*failure_errno = myerr;
+
 	strbuf_release(&sb_path);
 	strbuf_release(&sb_contents);
 	return ret;
 }
 
 int parse_loose_ref_contents(const char *buf, struct object_id *oid,
-			     struct strbuf *referent, unsigned int *type)
+			     struct strbuf *referent, unsigned int *type,
+			     int *failure_errno)
 {
 	const char *p;
 	if (skip_prefix(buf, "ref:", &buf)) {
@@ -486,7 +498,7 @@ int parse_loose_ref_contents(const char *buf, struct object_id *oid,
 	if (parse_oid_hex(buf, oid, &p) ||
 	    (*p != '\0' && !isspace(*p))) {
 		*type |= REF_ISBROKEN;
-		errno = EINVAL;
+		*failure_errno = EINVAL;
 		return -1;
 	}
 	return 0;
@@ -995,11 +1007,12 @@ static int create_reflock(const char *path, void *cb)
  * Locks a ref returning the lock on success and NULL on failure.
  */
 static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
-					   const char *refname, int *type,
+					   const char *refname,
 					   struct strbuf *err)
 {
 	struct strbuf ref_file = STRBUF_INIT;
 	struct ref_lock *lock;
+	int ignore_errno;
 
 	files_assert_main_repository(refs, "lock_ref_oid_basic");
 	assert(err);
@@ -1007,16 +1020,6 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 	CALLOC_ARRAY(lock, 1);
 
 	files_ref_path(refs, &ref_file, refname);
-	if (!refs_resolve_ref_unsafe(&refs->base, refname,
-				     RESOLVE_REF_NO_RECURSE,
-				     &lock->old_oid, type)) {
-		if (!refs_verify_refname_available(&refs->base, refname,
-						   NULL, NULL, err))
-			strbuf_addf(err, "unable to resolve reference '%s': %s",
-				    refname, strerror(errno));
-
-		goto error_return;
-	}
 
 	/*
 	 * If the ref did not exist and we are creating it, make sure
@@ -1036,9 +1039,8 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 		goto error_return;
 	}
 
-	if (refs_read_ref_full(&refs->base, lock->ref_name,
-			       0,
-			       &lock->old_oid, NULL))
+	if (!refs_resolve_ref_unsafe(&refs->base, lock->ref_name, 0,
+				     &lock->old_oid, NULL, &ignore_errno))
 		oidclr(&lock->old_oid);
 	goto out;
 
@@ -1358,6 +1360,35 @@ static int commit_ref_update(struct files_ref_store *refs,
 			     const struct object_id *oid, const char *logmsg,
 			     struct strbuf *err);
 
+/*
+ * Emit a better error message than lockfile.c's
+ * unable_to_lock_message() would in case there is a D/F conflict with
+ * another existing reference. If there would be a conflict, emit an error
+ * message and return false; otherwise, return true.
+ *
+ * Note that this function is not safe against all races with other
+ * processes, and that's not its job. We'll emit a more verbose error on D/f
+ * conflicts if we get past it into lock_ref_oid_basic().
+ */
+static 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;
+}
+
 static int files_copy_or_rename_ref(struct ref_store *ref_store,
 			    const char *oldrefname, const char *newrefname,
 			    const char *logmsg, int copy)
@@ -1373,6 +1404,7 @@ static int files_copy_or_rename_ref(struct ref_store *ref_store,
 	struct strbuf tmp_renamed_log = STRBUF_INIT;
 	int log, ret;
 	struct strbuf err = STRBUF_INIT;
+	int ignore_errno;
 
 	files_reflog_path(refs, &sb_oldref, oldrefname);
 	files_reflog_path(refs, &sb_newref, newrefname);
@@ -1386,7 +1418,7 @@ static int files_copy_or_rename_ref(struct ref_store *ref_store,
 
 	if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
 				     RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-				&orig_oid, &flag)) {
+				     &orig_oid, &flag, &ignore_errno)) {
 		ret = error("refname %s not found", oldrefname);
 		goto out;
 	}
@@ -1430,9 +1462,9 @@ static int files_copy_or_rename_ref(struct ref_store *ref_store,
 	 * the safety anyway; we want to delete the reference whatever
 	 * its current value.
 	 */
-	if (!copy && !refs_read_ref_full(&refs->base, newrefname,
-				RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-				NULL, NULL) &&
+	if (!copy && refs_resolve_ref_unsafe(&refs->base, newrefname,
+					     RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+					     NULL, NULL, &ignore_errno) &&
 	    refs_delete_ref(&refs->base, NULL, newrefname,
 			    NULL, REF_NO_DEREF)) {
 		if (errno == EISDIR) {
@@ -1458,7 +1490,7 @@ static int files_copy_or_rename_ref(struct ref_store *ref_store,
 
 	logmoved = log;
 
-	lock = lock_ref_oid_basic(refs, newrefname, NULL, &err);
+	lock = lock_ref_oid_basic(refs, newrefname, &err);
 	if (!lock) {
 		if (copy)
 			error("unable to copy '%s' to '%s': %s", oldrefname, newrefname, err.buf);
@@ -1480,7 +1512,7 @@ static int files_copy_or_rename_ref(struct ref_store *ref_store,
 	goto out;
 
  rollback:
-	lock = lock_ref_oid_basic(refs, oldrefname, NULL, &err);
+	lock = lock_ref_oid_basic(refs, oldrefname, &err);
 	if (!lock) {
 		error("unable to lock %s for rollback: %s", oldrefname, err.buf);
 		strbuf_release(&err);
@@ -1797,10 +1829,12 @@ static int commit_ref_update(struct files_ref_store *refs,
 		 */
 		int head_flag;
 		const char *head_ref;
+		int ignore_errno;
 
 		head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
 						   RESOLVE_REF_READING,
-						   NULL, &head_flag);
+						   NULL, &head_flag,
+						   &ignore_errno);
 		if (head_ref && (head_flag & REF_ISSYMREF) &&
 		    !strcmp(head_ref, lock->ref_name)) {
 			struct strbuf log_err = STRBUF_INIT;
@@ -1844,9 +1878,12 @@ static void update_symref_reflog(struct files_ref_store *refs,
 {
 	struct strbuf err = STRBUF_INIT;
 	struct object_id new_oid;
+	int ignore_errno;
+
 	if (logmsg &&
-	    !refs_read_ref_full(&refs->base, target,
-				RESOLVE_REF_READING, &new_oid, NULL) &&
+	    refs_resolve_ref_unsafe(&refs->base, target,
+				    RESOLVE_REF_READING, &new_oid, NULL,
+				    &ignore_errno) &&
 	    files_log_ref_write(refs, refname, &lock->old_oid,
 				&new_oid, logmsg, 0, &err)) {
 		error("%s", err.buf);
@@ -1887,7 +1924,7 @@ static int files_create_symref(struct ref_store *ref_store,
 	struct ref_lock *lock;
 	int ret;
 
-	lock = lock_ref_oid_basic(refs, refname, NULL, &err);
+	lock = lock_ref_oid_basic(refs, refname, &err);
 	if (!lock) {
 		error("%s", err.buf);
 		strbuf_release(&err);
@@ -2120,6 +2157,7 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
 		(struct files_reflog_iterator *)ref_iterator;
 	struct dir_iterator *diter = iter->dir_iterator;
 	int ok;
+	int ignore_errno;
 
 	while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
 		int flags;
@@ -2131,9 +2169,10 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
 		if (ends_with(diter->basename, ".lock"))
 			continue;
 
-		if (refs_read_ref_full(iter->ref_store,
-				       diter->relative_path, 0,
-				       &iter->oid, &flags)) {
+		if (!refs_resolve_ref_unsafe(iter->ref_store,
+					     diter->relative_path, 0,
+					     &iter->oid, &flags,
+					     &ignore_errno)) {
 			error("bad ref for %s", diter->path.buf);
 			continue;
 		}
@@ -2477,9 +2516,11 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			 * the transaction, so we have to read it here
 			 * to record and possibly check old_oid:
 			 */
-			if (refs_read_ref_full(&refs->base,
-					       referent.buf, 0,
-					       &lock->old_oid, NULL)) {
+			int ignore_errno;
+			if (!refs_resolve_ref_unsafe(&refs->base,
+						     referent.buf, 0,
+						     &lock->old_oid, NULL,
+						     &ignore_errno)) {
 				if (update->flags & REF_HAVE_OLD) {
 					strbuf_addf(err, "cannot lock ref '%s': "
 						    "error reading reference",
@@ -3091,7 +3132,6 @@ static int files_reflog_expire(struct ref_store *ref_store,
 	struct strbuf log_file_sb = STRBUF_INIT;
 	char *log_file;
 	int status = 0;
-	int type;
 	struct strbuf err = STRBUF_INIT;
 	const struct object_id *oid;
 
@@ -3105,7 +3145,7 @@ static int files_reflog_expire(struct ref_store *ref_store,
 	 * reference itself, plus we might need to update the
 	 * reference if --updateref was specified:
 	 */
-	lock = lock_ref_oid_basic(refs, refname, &type, &err);
+	lock = lock_ref_oid_basic(refs, refname, &err);
 	if (!lock) {
 		error("cannot lock ref '%s': %s", refname, err.buf);
 		strbuf_release(&err);
@@ -3167,9 +3207,20 @@ static int files_reflog_expire(struct ref_store *ref_store,
 		 * a reference if there are no remaining reflog
 		 * entries.
 		 */
-		int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
-			!(type & REF_ISSYMREF) &&
-			!is_null_oid(&cb.last_kept_oid);
+		int update = 0;
+
+		if ((flags & EXPIRE_REFLOGS_UPDATE_REF) &&
+		    !is_null_oid(&cb.last_kept_oid)) {
+			int ignore_errno;
+			int type;
+			const char *ref;
+
+			ref = refs_resolve_ref_unsafe(&refs->base, refname,
+						      RESOLVE_REF_NO_RECURSE,
+						      NULL, &type,
+						      &ignore_errno);
+			update = !!(ref && !(type & REF_ISSYMREF));
+		}
 
 		if (close_lock_file_gently(&reflog_lock)) {
 			status |= error("couldn't write %s: %s", log_file,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 1c5211b03e..9da932a540 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1354,6 +1354,7 @@ int is_packed_transaction_needed(struct ref_store *ref_store,
 	ret = 0;
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
+		int failure_errno;
 		unsigned int type;
 		struct object_id oid;
 
@@ -1364,9 +1365,9 @@ int is_packed_transaction_needed(struct ref_store *ref_store,
 			 */
 			continue;
 
-		if (!refs_read_raw_ref(ref_store, update->refname,
-				       &oid, &referent, &type) ||
-		    errno != ENOENT) {
+		if (!refs_read_raw_ref(ref_store, update->refname, &oid,
+				       &referent, &type, &failure_errno) ||
+		    failure_errno != ENOENT) {
 			/*
 			 * We have to actually delete that reference
 			 * -> this transaction is needed.
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 12224742ed..fb2c58ce3b 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -150,9 +150,9 @@ struct ref_update {
 	const char refname[FLEX_ARRAY];
 };
 
-int refs_read_raw_ref(struct ref_store *ref_store,
-		      const char *refname, struct object_id *oid,
-		      struct strbuf *referent, unsigned int *type);
+int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
+		      struct object_id *oid, struct strbuf *referent,
+		      unsigned int *type, int *failure_errno);
 
 /*
  * Write an error to `err` and return a nonzero value iff the same
@@ -229,20 +229,6 @@ const char *find_descendant_ref(const char *dirname,
 				const struct string_list *extras,
 				const struct string_list *skip);
 
-/*
- * Check whether an attempt to rename old_refname to new_refname would
- * cause a D/F conflict with any existing reference (other than
- * possibly old_refname). If there would be a conflict, emit an error
- * message and return false; otherwise, return true.
- *
- * Note that this function is not safe against all races with other
- * processes (though rename_ref() catches some races that might get by
- * this check).
- */
-int refs_rename_ref_available(struct ref_store *refs,
-			      const char *old_refname,
-			      const char *new_refname);
-
 /* We allow "recursive" symbolic refs. Only within reason, though */
 #define SYMREF_MAXDEPTH 5
 
@@ -713,10 +699,12 @@ struct ref_store {
 };
 
 /*
- * Parse contents of a loose ref file.
+ * Parse contents of a loose ref file. *failure_errno maybe be set to EINVAL for
+ * invalid contents.
  */
 int parse_loose_ref_contents(const char *buf, struct object_id *oid,
-			     struct strbuf *referent, unsigned int *type);
+			     struct strbuf *referent, unsigned int *type,
+			     int *failure_errno);
 
 /*
  * Fill in the generic part of refs and add it to our collection of
diff --git a/sequencer.c b/sequencer.c
index cd2aabf1f7..86bad55b90 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1282,6 +1282,8 @@ void print_commit_summary(struct repository *r,
 	struct pretty_print_context pctx = {0};
 	struct strbuf author_ident = STRBUF_INIT;
 	struct strbuf committer_ident = STRBUF_INIT;
+	struct ref_store *refs;
+	int resolve_errno;
 
 	commit = lookup_commit(r, oid);
 	if (!commit)
@@ -1331,9 +1333,13 @@ void print_commit_summary(struct repository *r,
 	rev.diffopt.break_opt = 0;
 	diff_setup_done(&rev.diffopt);
 
-	head = resolve_ref_unsafe("HEAD", 0, NULL, NULL);
-	if (!head)
+	refs = get_main_ref_store(the_repository);
+	head = refs_resolve_ref_unsafe(refs, "HEAD", 0, NULL, NULL,
+				       &resolve_errno);
+	if (!head) {
+		errno = resolve_errno;
 		die_errno(_("unable to resolve HEAD after creating commit"));
+	}
 	if (!strcmp(head, "HEAD"))
 		head = _("detached HEAD");
 	else
diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c
index b314b81a45..3986665037 100644
--- a/t/helper/test-ref-store.c
+++ b/t/helper/test-ref-store.c
@@ -123,9 +123,10 @@ static int cmd_resolve_ref(struct ref_store *refs, const char **argv)
 	int resolve_flags = arg_flags(*argv++, "resolve-flags");
 	int flags;
 	const char *ref;
+	int ignore_errno;
 
 	ref = refs_resolve_ref_unsafe(refs, refname, resolve_flags,
-				      &oid, &flags);
+				      &oid, &flags, &ignore_errno);
 	printf("%s %s 0x%x\n", oid_to_hex(&oid), ref ? ref : "(null)", flags);
 	return ref ? 0 : 1;
 }
diff --git a/t/t1417-reflog-updateref.sh b/t/t1417-reflog-updateref.sh
new file mode 100755
index 0000000000..14f13b57c6
--- /dev/null
+++ b/t/t1417-reflog-updateref.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+test_description='git reflog --updateref'
+
+TEST_PASSES_SANITIZE_LEAK=true
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	git init -b main repo &&
+	(
+		cd repo &&
+
+		test_commit A &&
+		test_commit B &&
+		test_commit C &&
+
+		cp .git/logs/HEAD HEAD.old &&
+		git reset --hard HEAD~ &&
+		cp HEAD.old .git/logs/HEAD
+	)
+'
+
+test_reflog_updateref () {
+	exp=$1
+	shift
+	args="$@"
+
+	test_expect_success REFFILES "get '$exp' with '$args'"  '
+		test_when_finished "rm -rf copy" &&
+		cp -R repo copy &&
+
+		(
+			cd copy &&
+
+			$args &&
+			git rev-parse $exp >expect &&
+			git rev-parse HEAD >actual &&
+
+			test_cmp expect actual
+		)
+	'
+}
+
+test_reflog_updateref B git reflog delete --updateref HEAD@{0}
+test_reflog_updateref B git reflog delete --updateref HEAD@{1}
+test_reflog_updateref C git reflog delete --updateref main@{0}
+test_reflog_updateref B git reflog delete --updateref main@{1}
+test_reflog_updateref B git reflog delete --updateref --rewrite HEAD@{0}
+test_reflog_updateref B git reflog delete --updateref --rewrite HEAD@{1}
+test_reflog_updateref C git reflog delete --updateref --rewrite main@{0}
+test_reflog_updateref B git reflog delete --updateref --rewrite main@{1}
+test_reflog_updateref B test_must_fail git reflog expire  HEAD@{0}
+test_reflog_updateref B test_must_fail git reflog expire  HEAD@{1}
+test_reflog_updateref B test_must_fail git reflog expire  main@{0}
+test_reflog_updateref B test_must_fail git reflog expire  main@{1}
+test_reflog_updateref B test_must_fail git reflog expire --updateref HEAD@{0}
+test_reflog_updateref B test_must_fail git reflog expire --updateref HEAD@{1}
+test_reflog_updateref B test_must_fail git reflog expire --updateref main@{0}
+test_reflog_updateref B test_must_fail git reflog expire --updateref main@{1}
+test_reflog_updateref B test_must_fail git reflog expire --updateref --rewrite HEAD@{0}
+test_reflog_updateref B test_must_fail git reflog expire --updateref --rewrite HEAD@{1}
+test_reflog_updateref B test_must_fail git reflog expire --updateref --rewrite main@{0}
+test_reflog_updateref B test_must_fail git reflog expire --updateref --rewrite main@{1}
+
+test_done
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index e575ffb4ff..53e0d094bb 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -731,6 +731,28 @@ test_expect_success SYMLINKS 'git branch -m u v should fail when the reflog for
 	test_must_fail git branch -m u v
 '
 
+test_expect_success SYMLINKS 'git branch -m with symlinked .git/refs' '
+	test_when_finished "rm -rf subdir" &&
+	git init --bare subdir &&
+
+	rm -rfv subdir/refs subdir/objects subdir/packed-refs &&
+	ln -s ../.git/refs subdir/refs &&
+	ln -s ../.git/objects subdir/objects &&
+	ln -s ../.git/packed-refs subdir/packed-refs &&
+
+	git -C subdir rev-parse --absolute-git-dir >subdir.dir &&
+	git rev-parse --absolute-git-dir >our.dir &&
+	! test_cmp subdir.dir our.dir &&
+
+	git -C subdir log &&
+	git -C subdir branch rename-src &&
+	git rev-parse rename-src >expect &&
+	git -C subdir branch -m rename-src rename-dest &&
+	git rev-parse rename-dest >actual &&
+	test_cmp expect actual &&
+	git branch -D rename-dest
+'
+
 test_expect_success 'test tracking setup via --track' '
 	git config remote.local.url . &&
 	git config remote.local.fetch refs/heads/*:refs/remotes/local/* &&
diff --git a/worktree.c b/worktree.c
index 092a4f92ad..2c155b1015 100644
--- a/worktree.c
+++ b/worktree.c
@@ -28,11 +28,13 @@ static void add_head_info(struct worktree *wt)
 {
 	int flags;
 	const char *target;
+	int ignore_errno;
 
 	target = refs_resolve_ref_unsafe(get_worktree_ref_store(wt),
 					 "HEAD",
 					 0,
-					 &wt->head_oid, &flags);
+					 &wt->head_oid, &flags,
+					 &ignore_errno);
 	if (!target)
 		return;
 
@@ -418,6 +420,7 @@ const struct worktree *find_shared_symref(const char *symref,
 		const char *symref_target;
 		struct ref_store *refs;
 		int flags;
+		int ignore_errno;
 
 		if (wt->is_bare)
 			continue;
@@ -435,7 +438,8 @@ const struct worktree *find_shared_symref(const char *symref,
 
 		refs = get_worktree_ref_store(wt);
 		symref_target = refs_resolve_ref_unsafe(refs, symref, 0,
-							NULL, &flags);
+							NULL, &flags,
+							&ignore_errno);
 		if ((flags & REF_ISSYMREF) &&
 		    symref_target && !strcmp(symref_target, target)) {
 			existing = wt;
@@ -563,16 +567,17 @@ int other_head_refs(each_ref_fn fn, void *cb_data)
 		struct worktree *wt = *p;
 		struct object_id oid;
 		int flag;
+		int ignore_errno;
 
 		if (wt->is_current)
 			continue;
 
 		strbuf_reset(&refname);
 		strbuf_worktree_ref(wt, &refname, "HEAD");
-		if (!refs_read_ref_full(get_main_ref_store(the_repository),
-					refname.buf,
-					RESOLVE_REF_READING,
-					&oid, &flag))
+		if (refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
+					    refname.buf,
+					    RESOLVE_REF_READING,
+					    &oid, &flag, &ignore_errno))
 			ret = fn(refname.buf, &oid, flag, cb_data);
 		if (ret)
 			break;