Merge branch 'sj/ref-fsck'

"git fsck" infrastructure has been taught to also check the sanity
of the ref database, in addition to the object database.

* sj/ref-fsck:
  fsck: add ref name check for files backend
  files-backend: add unified interface for refs scanning
  builtin/refs: add verify subcommand
  refs: set up ref consistency check infrastructure
  fsck: add refs report function
  fsck: add a unified interface for reporting fsck messages
  fsck: make "fsck_error" callback generic
  fsck: rename objects-related fsck error functions
  fsck: rename "skiplist" to "skip_oids"

Documentation/fsck-msgids.txt

@@ -19,6 +19,12 @@
 `badParentSha1`::
 	(ERROR) A commit object has a bad parent sha1.
 
+`badRefFiletype`::
+	(ERROR) A ref has a bad file type.
+
+`badRefName`::
+	(ERROR) A ref has an invalid format.
+
 `badTagName`::
 	(INFO) A tag has an invalid format.
 

Documentation/git-refs.txt

@@ -10,6 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git refs migrate' --ref-format=<format> [--dry-run]
+'git refs verify' [--strict] [--verbose]
 
 DESCRIPTION
 -----------
@@ -22,6 +23,9 @@ COMMANDS
 migrate::
 	Migrate ref store between different formats.
 
+verify::
+	Verify reference database consistency.
+
 OPTIONS
 -------
 
@@ -39,6 +43,15 @@ include::ref-storage-format.txt[]
 	can be used to double check that the migration works as expected before
 	performing the actual migration.
 
+The following options are specific to 'git refs verify':
+
+--strict::
+	Enable stricter error checking. This will cause warnings to be
+	reported as errors. See linkgit:git-fsck[1].
+
+--verbose::
+	When verifying the reference database consistency, be chatty.
+
 KNOWN LIMITATIONS
 -----------------
 

builtin/fsck.c

@@ -89,13 +89,16 @@ static int objerror(struct object *obj, const char *err)
 	return -1;
 }
 
-static int fsck_error_func(struct fsck_options *o UNUSED,
+static int fsck_objects_error_func(struct fsck_options *o UNUSED,
-			   const struct object_id *oid,
+				   void *fsck_report,
-			   enum object_type object_type,
+				   enum fsck_msg_type msg_type,
-			   enum fsck_msg_type msg_type,
+				   enum fsck_msg_id msg_id UNUSED,
-			   enum fsck_msg_id msg_id UNUSED,
+				   const char *message)
-			   const char *message)
 {
+	struct fsck_object_report *report = fsck_report;
+	const struct object_id *oid = report->oid;
+	enum object_type object_type = report->object_type;
+
 	switch (msg_type) {
 	case FSCK_WARN:
 		/* TRANSLATORS: e.g. warning in tree 01bfda: <more explanation> */
@@ -938,7 +941,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 
 	fsck_walk_options.walk = mark_object;
 	fsck_obj_options.walk = mark_used;
-	fsck_obj_options.error_func = fsck_error_func;
+	fsck_obj_options.error_func = fsck_objects_error_func;
 	if (check_strict)
 		fsck_obj_options.strict = 1;
 

builtin/mktag.c

@@ -18,8 +18,7 @@ static int option_strict = 1;
 static struct fsck_options fsck_options = FSCK_OPTIONS_STRICT;
 
 static int mktag_fsck_error_func(struct fsck_options *o UNUSED,
-				 const struct object_id *oid UNUSED,
+				 void *fsck_report UNUSED,
-				 enum object_type object_type UNUSED,
 				 enum fsck_msg_type msg_type,
 				 enum fsck_msg_id msg_id UNUSED,
 				 const char *message)

builtin/refs.c

@@ -1,4 +1,6 @@
 #include "builtin.h"
+#include "config.h"
+#include "fsck.h"
 #include "parse-options.h"
 #include "refs.h"
 #include "repository.h"
@@ -7,6 +9,9 @@
 #define REFS_MIGRATE_USAGE \
 	N_("git refs migrate --ref-format=<format> [--dry-run]")
 
+#define REFS_VERIFY_USAGE \
+	N_("git refs verify [--strict] [--verbose]")
+
 static int cmd_refs_migrate(int argc, const char **argv, const char *prefix)
 {
 	const char * const migrate_usage[] = {
@@ -58,15 +63,44 @@ out:
 	return err;
 }
 
+static int cmd_refs_verify(int argc, const char **argv, const char *prefix)
+{
+	struct fsck_options fsck_refs_options = FSCK_REFS_OPTIONS_DEFAULT;
+	const char * const verify_usage[] = {
+		REFS_VERIFY_USAGE,
+		NULL,
+	};
+	struct option options[] = {
+		OPT_BOOL(0, "verbose", &fsck_refs_options.verbose, N_("be verbose")),
+		OPT_BOOL(0, "strict", &fsck_refs_options.strict, N_("enable strict checking")),
+		OPT_END(),
+	};
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, verify_usage, 0);
+	if (argc)
+		usage(_("'git refs verify' takes no arguments"));
+
+	git_config(git_fsck_config, &fsck_refs_options);
+	prepare_repo_settings(the_repository);
+
+	ret = refs_fsck(get_main_ref_store(the_repository), &fsck_refs_options);
+
+	fsck_options_clear(&fsck_refs_options);
+	return ret;
+}
+
 int cmd_refs(int argc, const char **argv, const char *prefix)
 {
 	const char * const refs_usage[] = {
 		REFS_MIGRATE_USAGE,
+		REFS_VERIFY_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
 	struct option opts[] = {
 		OPT_SUBCOMMAND("migrate", &fn, cmd_refs_migrate),
+		OPT_SUBCOMMAND("verify", &fn, cmd_refs_verify),
 		OPT_END(),
 	};
 

fsck.c

@@ -205,7 +205,7 @@ void fsck_set_msg_types(struct fsck_options *options, const char *values)
 		if (!strcmp(buf, "skiplist")) {
 			if (equal == len)
 				die("skiplist requires a path");
-			oidset_parse_file(&options->skiplist, buf + equal + 1,
+			oidset_parse_file(&options->skip_oids, buf + equal + 1,
 					  the_repository->hash_algo);
 			buf += len + 1;
 			continue;
@@ -223,15 +223,18 @@ void fsck_set_msg_types(struct fsck_options *options, const char *values)
 static int object_on_skiplist(struct fsck_options *opts,
 			      const struct object_id *oid)
 {
-	return opts && oid && oidset_contains(&opts->skiplist, oid);
+	return opts && oid && oidset_contains(&opts->skip_oids, oid);
 }
 
-__attribute__((format (printf, 5, 6)))
+/*
-static int report(struct fsck_options *options,
+ * Provide the common functionality for either fscking refs or objects.
-		  const struct object_id *oid, enum object_type object_type,
+ * It will get the current msg error type and call the error_func callback
-		  enum fsck_msg_id msg_id, const char *fmt, ...)
+ * which is registered in the "fsck_options" struct.
+ */
+static int fsck_vreport(struct fsck_options *options,
+			void *fsck_report,
+			enum fsck_msg_id msg_id, const char *fmt, va_list ap)
 {
-	va_list ap;
 	struct strbuf sb = STRBUF_INIT;
 	enum fsck_msg_type msg_type = fsck_msg_type(msg_id, options);
 	int result;
@@ -239,9 +242,6 @@ static int report(struct fsck_options *options,
 	if (msg_type == FSCK_IGNORE)
 		return 0;
 
-	if (object_on_skiplist(options, oid))
-		return 0;
-
 	if (msg_type == FSCK_FATAL)
 		msg_type = FSCK_ERROR;
 	else if (msg_type == FSCK_INFO)
@@ -250,16 +250,49 @@ static int report(struct fsck_options *options,
 	prepare_msg_ids();
 	strbuf_addf(&sb, "%s: ", msg_id_info[msg_id].camelcased);
 
-	va_start(ap, fmt);
 	strbuf_vaddf(&sb, fmt, ap);
-	result = options->error_func(options, oid, object_type,
+	result = options->error_func(options, fsck_report,
 				     msg_type, msg_id, sb.buf);
 	strbuf_release(&sb);
+
+	return result;
+}
+
+__attribute__((format (printf, 5, 6)))
+static int report(struct fsck_options *options,
+		  const struct object_id *oid, enum object_type object_type,
+		  enum fsck_msg_id msg_id, const char *fmt, ...)
+{
+	va_list ap;
+	struct fsck_object_report report = {
+		.oid = oid,
+		.object_type = object_type
+	};
+	int result;
+
+	if (object_on_skiplist(options, oid))
+		return 0;
+
+	va_start(ap, fmt);
+	result = fsck_vreport(options, &report, msg_id, fmt, ap);
 	va_end(ap);
 
 	return result;
 }
 
+int fsck_report_ref(struct fsck_options *options,
+		    struct fsck_ref_report *report,
+		    enum fsck_msg_id msg_id,
+		    const char *fmt, ...)
+{
+	va_list ap;
+	int result;
+	va_start(ap, fmt);
+	result = fsck_vreport(options, report, msg_id, fmt, ap);
+	va_end(ap);
+	return result;
+}
+
 void fsck_enable_object_names(struct fsck_options *options)
 {
 	if (!options->object_names)
@@ -1200,13 +1233,15 @@ int fsck_buffer(const struct object_id *oid, enum object_type type,
 		      type);
 }
 
-int fsck_error_function(struct fsck_options *o,
+int fsck_objects_error_function(struct fsck_options *o,
-			const struct object_id *oid,
+				void *fsck_report,
-			enum object_type object_type UNUSED,
+				enum fsck_msg_type msg_type,
-			enum fsck_msg_type msg_type,
+				enum fsck_msg_id msg_id UNUSED,
-			enum fsck_msg_id msg_id UNUSED,
+				const char *message)
-			const char *message)
 {
+	struct fsck_object_report *report = fsck_report;
+	const struct object_id *oid = report->oid;
+
 	if (msg_type == FSCK_WARN) {
 		warning("object %s: %s", fsck_describe_object(o, oid), message);
 		return 0;
@@ -1215,6 +1250,32 @@ int fsck_error_function(struct fsck_options *o,
 	return 1;
 }
 
+int fsck_refs_error_function(struct fsck_options *options UNUSED,
+			     void *fsck_report,
+			     enum fsck_msg_type msg_type,
+			     enum fsck_msg_id msg_id UNUSED,
+			     const char *message)
+{
+	struct fsck_ref_report *report = fsck_report;
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	strbuf_addstr(&sb, report->path);
+
+	if (report->oid)
+		strbuf_addf(&sb, " -> (%s)", oid_to_hex(report->oid));
+	else if (report->referent)
+		strbuf_addf(&sb, " -> (%s)", report->referent);
+
+	if (msg_type == FSCK_WARN)
+		warning("%s: %s", sb.buf, message);
+	else
+		ret = error("%s: %s", sb.buf, message);
+
+	strbuf_release(&sb);
+	return ret;
+}
+
 static int fsck_blobs(struct oidset *blobs_found, struct oidset *blobs_done,
 		      enum fsck_msg_id msg_missing, enum fsck_msg_id msg_type,
 		      struct fsck_options *options, const char *blob_type)
@@ -1270,6 +1331,17 @@ int fsck_finish(struct fsck_options *options)
 	return ret;
 }
 
+void fsck_options_clear(struct fsck_options *options)
+{
+	free(options->msg_type);
+	oidset_clear(&options->skip_oids);
+	oidset_clear(&options->gitmodules_found);
+	oidset_clear(&options->gitmodules_done);
+	oidset_clear(&options->gitattributes_found);
+	oidset_clear(&options->gitattributes_done);
+	kh_clear_oid_map(options->object_names);
+}
+
 int git_fsck_config(const char *var, const char *value,
 		    const struct config_context *ctx, void *cb)
 {
@@ -1303,16 +1375,17 @@ int git_fsck_config(const char *var, const char *value,
  * Custom error callbacks that are used in more than one place.
  */
 
-int fsck_error_cb_print_missing_gitmodules(struct fsck_options *o,
+int fsck_objects_error_cb_print_missing_gitmodules(struct fsck_options *o,
-					   const struct object_id *oid,
+						   void *fsck_report,
-					   enum object_type object_type,
+						   enum fsck_msg_type msg_type,
-					   enum fsck_msg_type msg_type,
+						   enum fsck_msg_id msg_id,
-					   enum fsck_msg_id msg_id,
+						   const char *message)
-					   const char *message)
 {
 	if (msg_id == FSCK_MSG_GITMODULES_MISSING) {
-		puts(oid_to_hex(oid));
+		struct fsck_object_report *report = fsck_report;
+		puts(oid_to_hex(report->oid));
 		return 0;
 	}
-	return fsck_error_function(o, oid, object_type, msg_type, msg_id, message);
+	return fsck_objects_error_function(o, fsck_report,
+					   msg_type, msg_id, message);
 }

fsck.h

@@ -31,6 +31,8 @@ enum fsck_msg_type {
 	FUNC(BAD_NAME, ERROR) \
 	FUNC(BAD_OBJECT_SHA1, ERROR) \
 	FUNC(BAD_PARENT_SHA1, ERROR) \
+	FUNC(BAD_REF_FILETYPE, ERROR) \
+	FUNC(BAD_REF_NAME, ERROR) \
 	FUNC(BAD_TIMEZONE, ERROR) \
 	FUNC(BAD_TREE, ERROR) \
 	FUNC(BAD_TREE_SHA1, ERROR) \
@@ -114,29 +116,49 @@ int is_valid_msg_type(const char *msg_id, const char *msg_type);
 typedef int (*fsck_walk_func)(struct object *obj, enum object_type object_type,
 			      void *data, struct fsck_options *options);
 
-/* callback for fsck_object, type is FSCK_ERROR or FSCK_WARN */
+/*
+ * Callback for reporting errors either for objects or refs. The "fsck_report"
+ * is a generic pointer that can be used to pass any information.
+ */
 typedef int (*fsck_error)(struct fsck_options *o,
-			  const struct object_id *oid, enum object_type object_type,
+			  void *fsck_report,
 			  enum fsck_msg_type msg_type, enum fsck_msg_id msg_id,
 			  const char *message);
 
-int fsck_error_function(struct fsck_options *o,
+int fsck_objects_error_function(struct fsck_options *o,
-			const struct object_id *oid, enum object_type object_type,
+				void *fsck_report,
-			enum fsck_msg_type msg_type, enum fsck_msg_id msg_id,
+				enum fsck_msg_type msg_type, enum fsck_msg_id msg_id,
-			const char *message);
+				const char *message);
-int fsck_error_cb_print_missing_gitmodules(struct fsck_options *o,
+int fsck_objects_error_cb_print_missing_gitmodules(struct fsck_options *o,
-					   const struct object_id *oid,
+						   void *fsck_report,
-					   enum object_type object_type,
+						   enum fsck_msg_type msg_type,
-					   enum fsck_msg_type msg_type,
+						   enum fsck_msg_id msg_id,
-					   enum fsck_msg_id msg_id,
+						   const char *message);
-					   const char *message);
+
+int fsck_refs_error_function(struct fsck_options *options,
+			     void *fsck_report,
+			     enum fsck_msg_type msg_type,
+			     enum fsck_msg_id msg_id,
+			     const char *message);
+
+struct fsck_object_report {
+	const struct object_id *oid;
+	enum object_type object_type;
+};
+
+struct fsck_ref_report {
+	const char *path;
+	const struct object_id *oid;
+	const char *referent;
+};
 
 struct fsck_options {
 	fsck_walk_func walk;
 	fsck_error error_func;
-	unsigned strict:1;
+	unsigned strict;
+	unsigned verbose;
 	enum fsck_msg_type *msg_type;
-	struct oidset skiplist;
+	struct oidset skip_oids;
 	struct oidset gitmodules_found;
 	struct oidset gitmodules_done;
 	struct oidset gitattributes_found;
@@ -145,12 +167,12 @@ struct fsck_options {
 };
 
 #define FSCK_OPTIONS_DEFAULT { \
-	.skiplist = OIDSET_INIT, \
+	.skip_oids = OIDSET_INIT, \
 	.gitmodules_found = OIDSET_INIT, \
 	.gitmodules_done = OIDSET_INIT, \
 	.gitattributes_found = OIDSET_INIT, \
 	.gitattributes_done = OIDSET_INIT, \
-	.error_func = fsck_error_function \
+	.error_func = fsck_objects_error_function \
 }
 #define FSCK_OPTIONS_STRICT { \
 	.strict = 1, \
@@ -158,7 +180,7 @@ struct fsck_options {
 	.gitmodules_done = OIDSET_INIT, \
 	.gitattributes_found = OIDSET_INIT, \
 	.gitattributes_done = OIDSET_INIT, \
-	.error_func = fsck_error_function, \
+	.error_func = fsck_objects_error_function, \
 }
 #define FSCK_OPTIONS_MISSING_GITMODULES { \
 	.strict = 1, \
@@ -166,7 +188,10 @@ struct fsck_options {
 	.gitmodules_done = OIDSET_INIT, \
 	.gitattributes_found = OIDSET_INIT, \
 	.gitattributes_done = OIDSET_INIT, \
-	.error_func = fsck_error_cb_print_missing_gitmodules, \
+	.error_func = fsck_objects_error_cb_print_missing_gitmodules, \
+}
+#define FSCK_REFS_OPTIONS_DEFAULT { \
+	.error_func = fsck_refs_error_function, \
 }
 
 /* descend in all linked child objects
@@ -209,6 +234,21 @@ int fsck_tag_standalone(const struct object_id *oid, const char *buffer,
  */
 int fsck_finish(struct fsck_options *options);
 
+/*
+ * Clear the fsck_options struct, freeing any allocated memory.
+ */
+void fsck_options_clear(struct fsck_options *options);
+
+/*
+ * Report an error or warning for refs.
+ */
+__attribute__((format (printf, 4, 5)))
+int fsck_report_ref(struct fsck_options *options,
+		    struct fsck_ref_report *report,
+		    enum fsck_msg_id msg_id,
+		    const char *fmt, ...);
+
+
 /*
  * Subsystem for storing human-readable names for each object.
  *

object-file.c

@@ -2470,11 +2470,10 @@ int repo_has_object_file(struct repository *r,
  * give more context.
  */
 static int hash_format_check_report(struct fsck_options *opts UNUSED,
-				     const struct object_id *oid UNUSED,
+				    void *fsck_report UNUSED,
-				     enum object_type object_type UNUSED,
+				    enum fsck_msg_type msg_type UNUSED,
-				     enum fsck_msg_type msg_type UNUSED,
+				    enum fsck_msg_id msg_id UNUSED,
-				     enum fsck_msg_id msg_id UNUSED,
+				    const char *message)
-				     const char *message)
 {
 	error(_("object fails fsck: %s"), message);
 	return 1;

refs.c

@@ -316,6 +316,11 @@ int check_refname_format(const char *refname, int flags)
 	return check_or_sanitize_refname(refname, flags, NULL);
 }
 
+int refs_fsck(struct ref_store *refs, struct fsck_options *o)
+{
+	return refs->be->fsck(refs, o);
+}
+
 void sanitize_refname_component(const char *refname, struct strbuf *out)
 {
 	if (check_or_sanitize_refname(refname, REFNAME_ALLOW_ONELEVEL, out))

refs.h

@@ -4,6 +4,7 @@
 #include "commit.h"
 #include "repository.h"
 
+struct fsck_options;
 struct object_id;
 struct ref_store;
 struct strbuf;
@@ -541,6 +542,13 @@ int refs_for_each_reflog(struct ref_store *refs, each_reflog_fn fn, void *cb_dat
  */
 int check_refname_format(const char *refname, int flags);
 
+/*
+ * Check the reference database for consistency. Return 0 if refs and
+ * reflogs are consistent, and non-zero otherwise. The errors will be
+ * written to stderr.
+ */
+int refs_fsck(struct ref_store *refs, struct fsck_options *o);
+
 /*
  * Apply the rules from check_refname_format, but mutate the result until it
  * is acceptable, and place the result in "out".

refs/debug.c

@@ -419,6 +419,15 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 	return res;
 }
 
+static int debug_fsck(struct ref_store *ref_store,
+		      struct fsck_options *o)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->fsck(drefs->refs, o);
+	trace_printf_key(&trace_refs, "fsck: %d\n", res);
+	return res;
+}
+
 struct ref_storage_be refs_be_debug = {
 	.name = "debug",
 	.init = NULL,
@@ -451,4 +460,6 @@ struct ref_storage_be refs_be_debug = {
 	.create_reflog = debug_create_reflog,
 	.delete_reflog = debug_delete_reflog,
 	.reflog_expire = debug_reflog_expire,
+
+	.fsck = debug_fsck,
 };

refs/files-backend.c

@@ -4,6 +4,7 @@
 #include "../gettext.h"
 #include "../hash.h"
 #include "../hex.h"
+#include "../fsck.h"
 #include "../refs.h"
 #include "refs-internal.h"
 #include "ref-cache.h"
@@ -3419,6 +3420,116 @@ static int files_ref_store_remove_on_disk(struct ref_store *ref_store,
 	return ret;
 }
 
+/*
+ * For refs and reflogs, they share a unified interface when scanning
+ * the whole directory. This function is used as the callback for each
+ * regular file or symlink in the directory.
+ */
+typedef int (*files_fsck_refs_fn)(struct ref_store *ref_store,
+				  struct fsck_options *o,
+				  const char *refs_check_dir,
+				  struct dir_iterator *iter);
+
+static int files_fsck_refs_name(struct ref_store *ref_store UNUSED,
+				struct fsck_options *o,
+				const char *refs_check_dir,
+				struct dir_iterator *iter)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	/*
+	 * Ignore the files ending with ".lock" as they may be lock files
+	 * However, do not allow bare ".lock" files.
+	 */
+	if (iter->basename[0] != '.' && ends_with(iter->basename, ".lock"))
+		goto cleanup;
+
+	if (check_refname_format(iter->basename, REFNAME_ALLOW_ONELEVEL)) {
+		struct fsck_ref_report report = { .path = NULL };
+
+		strbuf_addf(&sb, "%s/%s", refs_check_dir, iter->relative_path);
+		report.path = sb.buf;
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_REF_NAME,
+				      "invalid refname format");
+	}
+
+cleanup:
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_fsck_refs_dir(struct ref_store *ref_store,
+			       struct fsck_options *o,
+			       const char *refs_check_dir,
+			       files_fsck_refs_fn *fsck_refs_fn)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct dir_iterator *iter;
+	int iter_status;
+	int ret = 0;
+
+	strbuf_addf(&sb, "%s/%s", ref_store->gitdir, refs_check_dir);
+
+	iter = dir_iterator_begin(sb.buf, 0);
+	if (!iter) {
+		ret = error_errno(_("cannot open directory %s"), sb.buf);
+		goto out;
+	}
+
+	while ((iter_status = dir_iterator_advance(iter)) == ITER_OK) {
+		if (S_ISDIR(iter->st.st_mode)) {
+			continue;
+		} else if (S_ISREG(iter->st.st_mode) ||
+			   S_ISLNK(iter->st.st_mode)) {
+			if (o->verbose)
+				fprintf_ln(stderr, "Checking %s/%s",
+					   refs_check_dir, iter->relative_path);
+			for (size_t i = 0; fsck_refs_fn[i]; i++) {
+				if (fsck_refs_fn[i](ref_store, o, refs_check_dir, iter))
+					ret = -1;
+			}
+		} else {
+			struct fsck_ref_report report = { .path = iter->basename };
+			if (fsck_report_ref(o, &report,
+					    FSCK_MSG_BAD_REF_FILETYPE,
+					    "unexpected file type"))
+				ret = -1;
+		}
+	}
+
+	if (iter_status != ITER_DONE)
+		ret = error(_("failed to iterate over '%s'"), sb.buf);
+
+out:
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int files_fsck_refs(struct ref_store *ref_store,
+			   struct fsck_options *o)
+{
+	files_fsck_refs_fn fsck_refs_fn[]= {
+		files_fsck_refs_name,
+		NULL,
+	};
+
+	if (o->verbose)
+		fprintf_ln(stderr, _("Checking references consistency"));
+	return files_fsck_refs_dir(ref_store, o,  "refs", fsck_refs_fn);
+}
+
+static int files_fsck(struct ref_store *ref_store,
+		      struct fsck_options *o)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ, "fsck");
+
+	return files_fsck_refs(ref_store, o) |
+	       refs->packed_ref_store->be->fsck(refs->packed_ref_store, o);
+}
+
 struct ref_storage_be refs_be_files = {
 	.name = "files",
 	.init = files_ref_store_init,
@@ -3445,5 +3556,7 @@ struct ref_storage_be refs_be_files = {
 	.reflog_exists = files_reflog_exists,
 	.create_reflog = files_create_reflog,
 	.delete_reflog = files_delete_reflog,
-	.reflog_expire = files_reflog_expire
+	.reflog_expire = files_reflog_expire,
+
+	.fsck = files_fsck,
 };

refs/packed-backend.c

@@ -1733,6 +1733,12 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 	return empty_ref_iterator_begin();
 }
 
+static int packed_fsck(struct ref_store *ref_store,
+		       struct fsck_options *o)
+{
+	return 0;
+}
+
 struct ref_storage_be refs_be_packed = {
 	.name = "packed",
 	.init = packed_ref_store_init,
@@ -1760,4 +1766,6 @@ struct ref_storage_be refs_be_packed = {
 	.create_reflog = NULL,
 	.delete_reflog = NULL,
 	.reflog_expire = NULL,
+
+	.fsck = packed_fsck,
 };

refs/refs-internal.h

@@ -4,6 +4,7 @@
 #include "refs.h"
 #include "iterator.h"
 
+struct fsck_options;
 struct ref_transaction;
 
 /*
@@ -651,6 +652,9 @@ typedef int read_raw_ref_fn(struct ref_store *ref_store, const char *refname,
 typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refname,
 				 struct strbuf *referent);
 
+typedef int fsck_fn(struct ref_store *ref_store,
+		    struct fsck_options *o);
+
 struct ref_storage_be {
 	const char *name;
 	ref_store_init_fn *init;
@@ -678,6 +682,8 @@ struct ref_storage_be {
 	create_reflog_fn *create_reflog;
 	delete_reflog_fn *delete_reflog;
 	reflog_expire_fn *reflog_expire;
+
+	fsck_fn *fsck;
 };
 
 extern struct ref_storage_be refs_be_files;

refs/reftable-backend.c

@@ -2309,6 +2309,12 @@ done:
 	return ret;
 }
 
+static int reftable_be_fsck(struct ref_store *ref_store,
+			    struct fsck_options *o)
+{
+	return 0;
+}
+
 struct ref_storage_be refs_be_reftable = {
 	.name = "reftable",
 	.init = reftable_be_init,
@@ -2336,4 +2342,6 @@ struct ref_storage_be refs_be_reftable = {
 	.create_reflog = reftable_be_create_reflog,
 	.delete_reflog = reftable_be_delete_reflog,
 	.reflog_expire = reftable_be_reflog_expire,
+
+	.fsck = reftable_be_fsck,
 };

t/t0602-reffiles-fsck.sh

@@ -0,0 +1,92 @@
+#!/bin/sh
+
+test_description='Test reffiles backend consistency check'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+GIT_TEST_DEFAULT_REF_FORMAT=files
+export GIT_TEST_DEFAULT_REF_FORMAT
+TEST_PASSES_SANITIZE_LEAK=true
+
+. ./test-lib.sh
+
+test_expect_success 'ref name should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	branch_dir_prefix=.git/refs/heads &&
+	tag_dir_prefix=.git/refs/tags &&
+	cd repo &&
+
+	git commit --allow-empty -m initial &&
+	git checkout -b branch-1 &&
+	git tag tag-1 &&
+	git commit --allow-empty -m second &&
+	git checkout -b branch-2 &&
+	git tag tag-2 &&
+	git tag multi_hierarchy/tag-2 &&
+
+	cp $branch_dir_prefix/branch-1 $branch_dir_prefix/.branch-1 &&
+	test_must_fail git refs verify 2>err &&
+	cat >expect <<-EOF &&
+	error: refs/heads/.branch-1: badRefName: invalid refname format
+	EOF
+	rm $branch_dir_prefix/.branch-1 &&
+	test_cmp expect err &&
+
+	cp $branch_dir_prefix/branch-1 $branch_dir_prefix/@ &&
+	test_must_fail git refs verify 2>err &&
+	cat >expect <<-EOF &&
+	error: refs/heads/@: badRefName: invalid refname format
+	EOF
+	rm $branch_dir_prefix/@ &&
+	test_cmp expect err &&
+
+	cp $tag_dir_prefix/multi_hierarchy/tag-2 $tag_dir_prefix/multi_hierarchy/@ &&
+	test_must_fail git refs verify 2>err &&
+	cat >expect <<-EOF &&
+	error: refs/tags/multi_hierarchy/@: badRefName: invalid refname format
+	EOF
+	rm $tag_dir_prefix/multi_hierarchy/@ &&
+	test_cmp expect err &&
+
+	cp $tag_dir_prefix/tag-1 $tag_dir_prefix/tag-1.lock &&
+	git refs verify 2>err &&
+	rm $tag_dir_prefix/tag-1.lock &&
+	test_must_be_empty err &&
+
+	cp $tag_dir_prefix/tag-1 $tag_dir_prefix/.lock &&
+	test_must_fail git refs verify 2>err &&
+	cat >expect <<-EOF &&
+	error: refs/tags/.lock: badRefName: invalid refname format
+	EOF
+	rm $tag_dir_prefix/.lock &&
+	test_cmp expect err
+'
+
+test_expect_success 'ref name check should be adapted into fsck messages' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	branch_dir_prefix=.git/refs/heads &&
+	tag_dir_prefix=.git/refs/tags &&
+	cd repo &&
+	git commit --allow-empty -m initial &&
+	git checkout -b branch-1 &&
+	git tag tag-1 &&
+	git commit --allow-empty -m second &&
+	git checkout -b branch-2 &&
+	git tag tag-2 &&
+
+	cp $branch_dir_prefix/branch-1 $branch_dir_prefix/.branch-1 &&
+	git -c fsck.badRefName=warn refs verify 2>err &&
+	cat >expect <<-EOF &&
+	warning: refs/heads/.branch-1: badRefName: invalid refname format
+	EOF
+	rm $branch_dir_prefix/.branch-1 &&
+	test_cmp expect err &&
+
+	cp $branch_dir_prefix/branch-1 $branch_dir_prefix/@ &&
+	git -c fsck.badRefName=ignore refs verify 2>err &&
+	test_must_be_empty err
+'
+
+test_done