Merge pull request #2188 from libgit2/cmn/config-snapshot

Configuration snapshotting

15 files changed, 594 insertions, 266 deletions

diff --git a/include/git2/config.h b/include/git2/config.h
index 663b4f6ba..21a5825a5 100644
--- a/include/git2/config.h
+++ b/include/git2/config.h
@@ -226,6 +226,22 @@ GIT_EXTERN(int) git_config_open_level(
  */
 GIT_EXTERN(int) git_config_open_global(git_config **out, git_config *config);
 
+/**
+ * Create a snapshot of the configuration
+ *
+ * Create a snapshot of the current state of a configuration, which
+ * allows you to look into a consistent view of the configuration for
+ * looking up complex values (e.g. a remote, submodule).
+ *
+ * The string returned when querying such a config object is valid
+ * until it is freed.
+ *
+ * @param out pointer in which to store the snapshot config object
+ * @param config configuration to snapshot
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_config_snapshot(git_config **out, git_config *config);
+
 
 /**
  * Reload changed config files
@@ -312,7 +328,8 @@ GIT_EXTERN(int) git_config_get_bool(int *out, const git_config *cfg, const char
  * Get the value of a string config variable.
  *
  * The string is owned by the variable and should not be freed by the
- * user.
+ * user. The pointer will be valid until the next operation on this
+ * config object.
  *
  * All config files will be looked into, in the order of their
  * defined level. A higher level means a higher priority. The
@@ -353,6 +370,9 @@ GIT_EXTERN(int) git_config_multivar_iterator_new(git_config_iterator **out, cons
 /**
  * Return the current entry and advance the iterator
  *
+ * The pointers returned by this function are valid until the iterator
+ * is freed.
+ *
  * @param entry pointer to store the entry
  * @param iter the iterator
  * @return 0 or an error code. GIT_ITEROVER if the iteration has completed
@@ -451,6 +471,9 @@ GIT_EXTERN(int) git_config_delete_multivar(git_config *cfg, const char *name, co
  * If the callback returns a non-zero value, the function stops iterating
  * and returns that value to the caller.
  *
+ * The pointers passed to the callback are only valid as long as the
+ * iteration is ongoing.
+ *
  * @param cfg where to get the variables from
  * @param callback the function to call on each variable
  * @param payload the data to pass to the callback
@@ -491,6 +514,9 @@ GIT_EXTERN(int) git_config_iterator_glob_new(git_config_iterator **out, const gi
  * regular expression that filters which config keys are passed to the
  * callback.
  *
+ * The pointers passed to the callback are only valid as long as the
+ * iteration is ongoing.
+ *
  * @param cfg where to get the variables from
  * @param regexp regular expression to match against config names
  * @param callback the function to call on each variable
diff --git a/include/git2/repository.h b/include/git2/repository.h
index 04df25fd3..0f7119b76 100644
--- a/include/git2/repository.h
+++ b/include/git2/repository.h
@@ -408,13 +408,25 @@ GIT_EXTERN(int) git_repository_is_bare(git_repository *repo);
  * The configuration file must be freed once it's no longer
  * being used by the user.
  *
- * @param out Pointer to store the loaded config file
+ * @param out Pointer to store the loaded configuration
  * @param repo A repository object
  * @return 0, or an error code
  */
 GIT_EXTERN(int) git_repository_config(git_config **out, git_repository *repo);
 
 /**
+ * Get a snapshot of the repository's configuration
+ *
+ * Convenience function to take a snapshot from the repository's
+ * configuration.
+ *
+ * @param out Pointer to store the loaded configuration
+ * @param repo the repository
+ * @return 0, or an error code
+ */
+GIT_EXTERN(int) git_repository_config_snapshot(git_config **out, git_repository *repo);
+
+/**
  * Get the Object Database for this repository.
  *
  * If a custom ODB has not been set, the default
diff --git a/include/git2/sys/config.h b/include/git2/sys/config.h
index 46bb65293..85e0d6417 100644
--- a/include/git2/sys/config.h
+++ b/include/git2/sys/config.h
@@ -57,13 +57,15 @@ struct git_config_backend {
 
 	/* Open means open the file/database and parse if necessary */
 	int (*open)(struct git_config_backend *, git_config_level_t level);
-	int (*get)(const struct git_config_backend *, const char *key, const git_config_entry **entry);
+	int (*get)(struct git_config_backend *, const char *key, const git_config_entry **entry);
 	int (*set)(struct git_config_backend *, const char *key, const char *value);
 	int (*set_multivar)(git_config_backend *cfg, const char *name, const char *regexp, const char *value);
 	int (*del)(struct git_config_backend *, const char *key);
 	int (*del_multivar)(struct git_config_backend *, const char *key, const char *regexp);
 	int (*iterator)(git_config_iterator **, struct git_config_backend *);
 	int (*refresh)(struct git_config_backend *);
+	/** Produce a read-only version of this backend */
+	int (*snapshot)(struct git_config_backend **, struct git_config_backend *);
 	void (*free)(struct git_config_backend *);
 };
 #define GIT_CONFIG_BACKEND_VERSION 1
diff --git a/src/branch.c b/src/branch.c
index 63c6ec110..52760853b 100644
--- a/src/branch.c
+++ b/src/branch.c
@@ -306,17 +306,13 @@ int git_branch_name(
 
 static int retrieve_upstream_configuration(
 	const char **out,
-	git_repository *repo,
+	const git_config *config,
 	const char *canonical_branch_name,
 	const char *format)
 {
-	git_config *config;
 	git_buf buf = GIT_BUF_INIT;
 	int error;
 
-	if (git_repository_config__weakptr(&config, repo) < 0)
-		return -1;
-
 	if (git_buf_printf(&buf, format,
 		canonical_branch_name + strlen(GIT_REFS_HEADS_DIR)) < 0)
 			return -1;
@@ -336,6 +332,7 @@ int git_branch_upstream_name(
 	int error = -1;
 	git_remote *remote = NULL;
 	const git_refspec *refspec;
+	git_config *config;
 
 	assert(out && refname);
 
@@ -344,12 +341,15 @@ int git_branch_upstream_name(
 	if (!git_reference__is_branch(refname))
 		return not_a_local_branch(refname);
 
+	if ((error = git_repository_config_snapshot(&config, repo)) < 0)
+		return error;
+
 	if ((error = retrieve_upstream_configuration(
-		&remote_name, repo, refname, "branch.%s.remote")) < 0)
+		&remote_name, config, refname, "branch.%s.remote")) < 0)
 			goto cleanup;
 
 	if ((error = retrieve_upstream_configuration(
-		&merge_name, repo, refname, "branch.%s.merge")) < 0)
+		&merge_name, config, refname, "branch.%s.merge")) < 0)
 			goto cleanup;
 
 	if (!*remote_name || !*merge_name) {
@@ -378,6 +378,7 @@ int git_branch_upstream_name(
 	error = git_buf_set(out, git_buf_cstr(&buf), git_buf_len(&buf));
 
 cleanup:
+	git_config_free(config);
 	git_remote_free(remote);
 	git_buf_free(&buf);
 	return error;
diff --git a/src/config.c b/src/config.c
index f9d697197..75ffb4000 100644
--- a/src/config.c
+++ b/src/config.c
@@ -137,6 +137,38 @@ int git_config_open_ondisk(git_config **out, const char *path)
 	return error;
 }
 
+int git_config_snapshot(git_config **out, git_config *in)
+{
+	int error;
+	size_t i;
+	file_internal *internal;
+	git_config *config;
+
+	*out = NULL;
+
+	if (git_config_new(&config) < 0)
+		return -1;
+
+	git_vector_foreach(&in->files, i, internal) {
+		git_config_backend *b;
+
+		if ((error = internal->file->snapshot(&b, internal->file)) < 0)
+			goto on_error;
+
+		if ((error = git_config_add_backend(config, b, internal->level, 0)) < 0) {
+			b->free(b);
+			goto on_error;
+		}
+	}
+
+	*out = config;
+	return error;
+
+on_error:
+	git_config_free(config);
+	return error;
+}
+
 static int find_internal_file_by_level(
 	file_internal **internal_out,
 	const git_config *cfg,
diff --git a/src/config_file.c b/src/config_file.c
index bb26aa8a3..c09a032be 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -26,7 +26,7 @@ GIT__USE_STRMAP;
 typedef struct cvar_t {
 	struct cvar_t *next;
 	git_config_entry *entry;
-	int included; /* whether this is part of [include] */
+	bool included; /* whether this is part of [include] */
 } cvar_t;
 
 typedef struct git_config_file_iter {
@@ -87,28 +87,54 @@ struct reader {
 };
 
 typedef struct {
+	git_atomic refcount;
+	git_strmap *values;
+} refcounted_strmap;
+
+typedef struct {
 	git_config_backend parent;
+	/* mutex to coordinate accessing the values */
+	git_mutex values_mutex;
+	refcounted_strmap *values;
+	int readonly;
+} diskfile_header;
 
-	git_strmap *values;
+typedef struct {
+	diskfile_header header;
+
+	git_config_level_t level;
 
 	git_array_t(struct reader) readers;
 
 	char  *file_path;
-
-	git_config_level_t level;
 } diskfile_backend;
 
-static int config_parse(diskfile_backend *cfg_file, struct reader *reader, git_config_level_t level, int depth);
+typedef struct {
+	diskfile_header header;
+
+	diskfile_backend *snapshot_from;
+} diskfile_readonly_backend;
+
+static int config_parse(git_strmap *values, diskfile_backend *cfg_file, struct reader *reader, git_config_level_t level, int depth);
 static int parse_variable(struct reader *reader, char **var_name, char **var_value);
 static int config_write(diskfile_backend *cfg, const char *key, const regex_t *preg, const char *value);
 static char *escape_value(const char *ptr);
 
+int git_config_file__snapshot(git_config_backend **out, diskfile_backend *in);
+static int config_snapshot(git_config_backend **out, git_config_backend *in);
+
 static void set_parse_error(struct reader *reader, int col, const char *error_str)
 {
 	giterr_set(GITERR_CONFIG, "Failed to parse config file: %s (in %s:%d, column %d)",
 		error_str, reader->file_path, reader->line_number, col);
 }
 
+static int config_error_readonly(void)
+{
+	giterr_set(GITERR_CONFIG, "this backend is read-only");
+	return -1;
+}
+
 static void cvar_free(cvar_t *var)
 {
 	if (var == NULL)
@@ -120,18 +146,6 @@ static void cvar_free(cvar_t *var)
 	git__free(var);
 }
 
-static int cvar_length(cvar_t *var)
-{
-	int length = 0;
-
-	while (var) {
-		length++;
-		var = var->next;
-	}
-
-	return length;
-}
-
 int git_config_file_normalize_section(char *start, char *end)
 {
 	char *scan;
@@ -155,6 +169,30 @@ int git_config_file_normalize_section(char *start, char *end)
 	return 0;
 }
 
+/* Add or append the new config option */
+static int append_entry(git_strmap *values, cvar_t *var)
+{
+	git_strmap_iter pos;
+	cvar_t *existing;
+	int error = 0;
+
+	pos = git_strmap_lookup_index(values, var->entry->name);
+	if (!git_strmap_valid_index(values, pos)) {
+		git_strmap_insert(values, var->entry->name, var, error);
+	} else {
+		existing = git_strmap_value_at(values, pos);
+		while (existing->next != NULL) {
+			existing = existing->next;
+		}
+		existing->next = var;
+	}
+
+	if (error > 0)
+		error = 0;
+
+	return error;
+}
+
 static void free_vars(git_strmap *values)
 {
 	cvar_t *var = NULL;
@@ -172,6 +210,58 @@ static void free_vars(git_strmap *values)
 	git_strmap_free(values);
 }
 
+static void refcounted_strmap_free(refcounted_strmap *map)
+{
+	if (!map)
+		return;
+
+	if (git_atomic_dec(&map->refcount) != 0)
+		return;
+
+	free_vars(map->values);
+	git__free(map);
+}
+
+/**
+ * Take the current values map from the backend and increase its
+ * refcount. This is its own function to make sure we use the mutex to
+ * avoid the map pointer from changing under us.
+ */
+static refcounted_strmap *refcounted_strmap_take(diskfile_header *h)
+{
+	refcounted_strmap *map;
+
+	git_mutex_lock(&h->values_mutex);
+
+	map = h->values;
+	git_atomic_inc(&map->refcount);
+
+	git_mutex_unlock(&h->values_mutex);
+
+	return map;
+}
+
+static int refcounted_strmap_alloc(refcounted_strmap **out)
+{
+	refcounted_strmap *map;
+	int error;
+
+	map = git__calloc(1, sizeof(refcounted_strmap));
+	if (!map) {
+		giterr_set_oom();
+		return -1;
+	}
+
+	git_atomic_set(&map->refcount, 1);
+	if ((error = git_strmap_alloc(&map->values)) < 0) {
+		git__free(map);
+		return error;
+	}
+
+	*out = map;
+	return error;
+}
+
 static int config_open(git_config_backend *cfg, git_config_level_t level)
 {
 	int res;
@@ -180,13 +270,14 @@ static int config_open(git_config_backend *cfg, git_config_level_t level)
 
 	b->level = level;
 
-	if ((res = git_strmap_alloc(&b->values)) < 0)
+	if ((res = refcounted_strmap_alloc(&b->header.values)) < 0)
 		return res;
 
+	git_mutex_init(&b->header.values_mutex);
 	git_array_init(b->readers);
 	reader = git_array_alloc(b->readers);
 	if (!reader) {
-		git_strmap_free(b->values);
+		refcounted_strmap_free(b->header.values);
 		return -1;
 	}
 	memset(reader, 0, sizeof(struct reader));
@@ -202,9 +293,9 @@ static int config_open(git_config_backend *cfg, git_config_level_t level)
 	if (res == GIT_ENOTFOUND)
 		return 0;
 
-	if (res < 0 || (res = config_parse(b, reader, level, 0)) < 0) {
-		free_vars(b->values);
-		b->values = NULL;
+	if (res < 0 || (res = config_parse(b->header.values->values, b, reader, level, 0)) < 0) {
+		refcounted_strmap_free(b->header.values);
+		b->header.values = NULL;
 	}
 
 	reader = git_array_get(b->readers, 0);
@@ -213,44 +304,60 @@ static int config_open(git_config_backend *cfg, git_config_level_t level)
 	return res;
 }
 
+/* The meat of the refresh, as we want to use it in different places */
+static int config__refresh(git_config_backend *cfg)
+{
+	refcounted_strmap *values = NULL, *tmp;
+	diskfile_backend *b = (diskfile_backend *)cfg;
+	struct reader *reader = NULL;
+	int error = 0;
+
+	if ((error = refcounted_strmap_alloc(&values)) < 0)
+		goto out;
+
+	reader = git_array_get(b->readers, git_array_size(b->readers) - 1);
+
+	if ((error = config_parse(values->values, b, reader, b->level, 0)) < 0)
+		goto out;
+
+	git_mutex_lock(&b->header.values_mutex);
+
+	tmp = b->header.values;
+	b->header.values = values;
+	values = tmp;
+
+	git_mutex_unlock(&b->header.values_mutex);
+
+out:
+	refcounted_strmap_free(values);
+	git_buf_free(&reader->buffer);
+	return error;
+}
+
 static int config_refresh(git_config_backend *cfg)
 {
-	int res = 0, updated = 0, any_updated = 0;
+	int error = 0, updated = 0, any_updated = 0;
 	diskfile_backend *b = (diskfile_backend *)cfg;
-	git_strmap *old_values;
 	struct reader *reader = NULL;
 	uint32_t i;
 
 	for (i = 0; i < git_array_size(b->readers); i++) {
 		reader = git_array_get(b->readers, i);
-
-		res = git_futils_readbuffer_updated(
+		error = git_futils_readbuffer_updated(
 			&reader->buffer, reader->file_path,
 			&reader->file_mtime, &reader->file_size, &updated);
 
-		if (res < 0)
-			return (res == GIT_ENOTFOUND) ? 0 : res;
+		if (error < 0)
+			return (error == GIT_ENOTFOUND) ? 0 : error;
 
 		if (updated)
 			any_updated = 1;
 	}
 
 	if (!any_updated)
-		return (res == GIT_ENOTFOUND) ? 0 : res;
-
-	/* need to reload - store old values and prep for reload */
-	old_values = b->values;
-	if ((res = git_strmap_alloc(&b->values)) < 0) {
-		b->values = old_values;
-	} else if ((res = config_parse(b, reader, b->level, 0)) < 0) {
-		free_vars(b->values);
-		b->values = old_values;
-	} else {
-		free_vars(old_values);
-	}
+		return (error == GIT_ENOTFOUND) ? 0 : error;
 
-	git_buf_free(&reader->buffer);
-	return res;
+	return config__refresh(cfg);
 }
 
 static void backend_free(git_config_backend *_backend)
@@ -268,13 +375,14 @@ static void backend_free(git_config_backend *_backend)
 	git_array_clear(backend->readers);
 
 	git__free(backend->file_path);
-	free_vars(backend->values);
+	refcounted_strmap_free(backend->header.values);
 	git__free(backend);
 }
 
 static void config_iterator_free(
 	git_config_iterator* iter)
 {
+	iter->backend->free(iter->backend);
 	git__free(iter);
 }
 
@@ -283,12 +391,13 @@ static int config_iterator_next(
 	git_config_iterator *iter)
 {
 	git_config_file_iter *it = (git_config_file_iter *) iter;
-	diskfile_backend *b = (diskfile_backend *) it->parent.backend;
+	diskfile_header *h = (diskfile_header *) it->parent.backend;
+	git_strmap *values = h->values->values;
 	int err = 0;
 	cvar_t * var;
 
 	if (it->next_var == NULL) {
-		err = git_strmap_next((void**) &var, &(it->iter), b->values);
+		err = git_strmap_next((void**) &var, &(it->iter), values);
 	} else {
 		var = it->next_var;
 	}
@@ -308,15 +417,28 @@ static int config_iterator_new(
 	git_config_iterator **iter,
 	struct git_config_backend* backend)
 {
-	diskfile_backend *b = (diskfile_backend *)backend;
-	git_config_file_iter *it = git__calloc(1, sizeof(git_config_file_iter));
+	diskfile_header *h;
+	git_config_file_iter *it;
+	git_config_backend *snapshot;
+	diskfile_backend *b = (diskfile_backend *) backend;
+	int error;
 
-	GIT_UNUSED(b);
+	if ((error = config_snapshot(&snapshot, backend)) < 0)
+		return error;
 
+	if ((error = snapshot->open(snapshot, b->level)) < 0)
+		return error;
+
+	it = git__calloc(1, sizeof(git_config_file_iter));
 	GITERR_CHECK_ALLOC(it);
 
-	it->parent.backend = backend;
-	it->iter = git_strmap_begin(b->values);
+	h = (diskfile_header *)snapshot;
+
+	/* strmap_begin() is currently a macro returning 0 */
+	GIT_UNUSED(h);
+
+	it->parent.backend = snapshot;
+	it->iter = git_strmap_begin(h->values);
 	it->next_var = NULL;
 
 	it->parent.next = config_iterator_next;
@@ -328,8 +450,9 @@ static int config_iterator_new(
 
 static int config_set(git_config_backend *cfg, const char *name, const char *value)
 {
-	cvar_t *var = NULL, *old_var = NULL;
 	diskfile_backend *b = (diskfile_backend *)cfg;
+	refcounted_strmap *map;
+	git_strmap *values;
 	char *key, *esc_value = NULL;
 	khiter_t pos;
 	int rval, ret;
@@ -337,93 +460,82 @@ static int config_set(git_config_backend *cfg, const char *name, const char *val
 	if ((rval = git_config__normalize_name(name, &key)) < 0)
 		return rval;
 
+	map = refcounted_strmap_take(&b->header);
+	values = map->values;
+
 	/*
 	 * Try to find it in the existing values and update it if it
 	 * only has one value.
 	 */
-	pos = git_strmap_lookup_index(b->values, key);
-	if (git_strmap_valid_index(b->values, pos)) {
-		cvar_t *existing = git_strmap_value_at(b->values, pos);
-		char *tmp = NULL;
-
-		git__free(key);
+	pos = git_strmap_lookup_index(values, key);
+	if (git_strmap_valid_index(values, pos)) {
+		cvar_t *existing = git_strmap_value_at(values, pos);
 
 		if (existing->next != NULL) {
 			giterr_set(GITERR_CONFIG, "Multivar incompatible with simple set");
-			return -1;
+			ret = -1;
+			goto out;
 		}
 
 		/* don't update if old and new values already match */
 		if ((!existing->entry->value && !value) ||
-			(existing->entry->value && value && !strcmp(existing->entry->value, value)))
-			return 0;
-
-		if (value) {
-			tmp = git__strdup(value);
-			GITERR_CHECK_ALLOC(tmp);
-			esc_value = escape_value(value);
-			GITERR_CHECK_ALLOC(esc_value);
+			(existing->entry->value && value &&
+			 !strcmp(existing->entry->value, value))) {
+			ret = 0;
+			goto out;
 		}
-
-		git__free((void *)existing->entry->value);
-		existing->entry->value = tmp;
-
-		ret = config_write(b, existing->entry->name, NULL, esc_value);
-
-		git__free(esc_value);
-		return ret;
 	}
 
-	var = git__malloc(sizeof(cvar_t));
-	GITERR_CHECK_ALLOC(var);
-	memset(var, 0x0, sizeof(cvar_t));
-	var->entry = git__malloc(sizeof(git_config_entry));
-	GITERR_CHECK_ALLOC(var->entry);
-	memset(var->entry, 0x0, sizeof(git_config_entry));
-
-	var->entry->name = key;
-	var->entry->value = NULL;
+	/* No early returns due to sanity checks, let's write it out and refresh */
 
 	if (value) {
-		var->entry->value = git__strdup(value);
-		GITERR_CHECK_ALLOC(var->entry->value);
 		esc_value = escape_value(value);
 		GITERR_CHECK_ALLOC(esc_value);
 	}
 
-	if ((ret = config_write(b, key, NULL, esc_value)) < 0) {
-		git__free(esc_value);
-		cvar_free(var);
-		return ret;
-	}
+	if ((ret = config_write(b, key, NULL, esc_value)) < 0)
+		goto out;
 
-	git__free(esc_value);
-	git_strmap_insert2(b->values, key, var, old_var, rval);
-	if (rval < 0)
-		return -1;
-	if (old_var != NULL)
-		cvar_free(old_var);
+	ret = config_refresh(cfg);
 
-	return 0;
+out:
+	refcounted_strmap_free(map);
+	git__free(esc_value);
+	git__free(key);
+	return ret;
 }
 
 /*
  * Internal function that actually gets the value in string form
  */
-static int config_get(const git_config_backend *cfg, const char *key, const git_config_entry **out)
+static int config_get(git_config_backend *cfg, const char *key, const git_config_entry **out)
 {
-	diskfile_backend *b = (diskfile_backend *)cfg;
-	khiter_t pos = git_strmap_lookup_index(b->values, key);
+	diskfile_header *h = (diskfile_header *)cfg;
+	refcounted_strmap *map;
+	git_strmap *values;
+	khiter_t pos;
 	cvar_t *var;
+	int error;
+
+	if (!h->readonly && ((error = config_refresh(cfg)) < 0))
+		return error;
+
+	map = refcounted_strmap_take(h);
+	values = map->values;
+
+	pos = git_strmap_lookup_index(values, key);
 
 	/* no error message; the config system will write one */
-	if (!git_strmap_valid_index(b->values, pos))
+	if (!git_strmap_valid_index(values, pos)) {
+		refcounted_strmap_free(map);
 		return GIT_ENOTFOUND;
+	}
 
-	var = git_strmap_value_at(b->values, pos);
+	var = git_strmap_value_at(values, pos);
 	while (var->next)
 		var = var->next;
 
+	refcounted_strmap_free(map);
 	*out = var->entry;
 	return 0;
 }
@@ -431,9 +543,9 @@ static int config_get(const git_config_backend *cfg, const char *key, const git_
 static int config_set_multivar(
 	git_config_backend *cfg, const char *name, const char *regexp, const char *value)
 {
-	int replaced = 0;
-	cvar_t *var, *newvar;
 	diskfile_backend *b = (diskfile_backend *)cfg;
+	refcounted_strmap *map;
+	git_strmap *values;
 	char *key;
 	regex_t preg;
 	int result;
@@ -444,62 +556,33 @@ static int config_set_multivar(
 	if ((result = git_config__normalize_name(name, &key)) < 0)
 		return result;
 
-	pos = git_strmap_lookup_index(b->values, key);
-	if (!git_strmap_valid_index(b->values, pos)) {
+	map = refcounted_strmap_take(&b->header);
+	values = b->header.values->values;
+
+	pos = git_strmap_lookup_index(values, key);
+	if (!git_strmap_valid_index(values, pos)) {
 		/* If we don't have it, behave like a normal set */
 		result = config_set(cfg, name, value);
+		refcounted_strmap_free(map);
 		git__free(key);
 		return result;
 	}
 
-	var = git_strmap_value_at(b->values, pos);
-
 	result = regcomp(&preg, regexp, REG_EXTENDED);
 	if (result < 0) {
-		git__free(key);
 		giterr_set_regex(&preg, result);
-		regfree(&preg);
-		return -1;
-	}
-
-	for (;;) {
-		if (regexec(&preg, var->entry->value, 0, NULL, 0) == 0) {
-			char *tmp = git__strdup(value);
-			GITERR_CHECK_ALLOC(tmp);
-
-			git__free((void *)var->entry->value);
-			var->entry->value = tmp;
-			replaced = 1;
-		}
-
-		if (var->next == NULL)
-			break;
-
-		var = var->next;
+		result = -1;
+		goto out;
 	}
 
-	/* If we've reached the end of the variables and we haven't found it yet, we need to append it */
-	if (!replaced) {
-		newvar = git__malloc(sizeof(cvar_t));
-		GITERR_CHECK_ALLOC(newvar);
-		memset(newvar, 0x0, sizeof(cvar_t));
-		newvar->entry = git__malloc(sizeof(git_config_entry));
-		GITERR_CHECK_ALLOC(newvar->entry);
-		memset(newvar->entry, 0x0, sizeof(git_config_entry));
+	/* If we do have it, set call config_write() and reload */
+	if ((result = config_write(b, key, &preg, value)) < 0)
+		goto out;
 
-		newvar->entry->name = git__strdup(var->entry->name);
-		GITERR_CHECK_ALLOC(newvar->entry->name);
-
-		newvar->entry->value = git__strdup(value);
-		GITERR_CHECK_ALLOC(newvar->entry->value);
-
-		newvar->entry->level = var->entry->level;
-
-		var->next = newvar;
-	}
-
-	result = config_write(b, key, &preg, value);
+	result = config_refresh(cfg);
 
+out:
+	refcounted_strmap_free(map);
 	git__free(key);
 	regfree(&preg);
 
@@ -510,6 +593,7 @@ static int config_delete(git_config_backend *cfg, const char *name)
 {
 	cvar_t *var;
 	diskfile_backend *b = (diskfile_backend *)cfg;
+	refcounted_strmap *map;	git_strmap *values;
 	char *key;
 	int result;
 	khiter_t pos;
@@ -517,35 +601,37 @@ static int config_delete(git_config_backend *cfg, const char *name)
 	if ((result = git_config__normalize_name(name, &key)) < 0)
 		return result;
 
-	pos = git_strmap_lookup_index(b->values, key);
+	map = refcounted_strmap_take(&b->header);
+	values = b->header.values->values;
+
+	pos = git_strmap_lookup_index(values, key);
 	git__free(key);
 
-	if (!git_strmap_valid_index(b->values, pos)) {
+	if (!git_strmap_valid_index(values, pos)) {
+		refcounted_strmap_free(map);
 		giterr_set(GITERR_CONFIG, "Could not find key '%s' to delete", name);
 		return GIT_ENOTFOUND;
 	}
 
-	var = git_strmap_value_at(b->values, pos);
+	var = git_strmap_value_at(values, pos);
+	refcounted_strmap_free(map);
 
 	if (var->next != NULL) {
 		giterr_set(GITERR_CONFIG, "Cannot delete multivar with a single delete");
 		return -1;
 	}
 
-	git_strmap_delete_at(b->values, pos);
-
-	result = config_write(b, var->entry->name, NULL, NULL);
+	if ((result = config_write(b, var->entry->name, NULL, NULL)) < 0)
+		return result;
 
-	cvar_free(var);
-	return result;
+	return config_refresh(cfg);
 }
 
 static int config_delete_multivar(git_config_backend *cfg, const char *name, const char *regexp)
 {
-	cvar_t *var, *prev = NULL, *new_head = NULL;
-	cvar_t **to_delete;
-	int to_delete_idx;
 	diskfile_backend *b = (diskfile_backend *)cfg;
+	refcounted_strmap *map;
+	git_strmap *values;
 	char *key;
 	regex_t preg;
 	int result;
@@ -554,66 +640,45 @@ static int config_delete_multivar(git_config_backend *cfg, const char *name, con
 	if ((result = git_config__normalize_name(name, &key)) < 0)
 		return result;
 
-	pos = git_strmap_lookup_index(b->values, key);
+	map = refcounted_strmap_take(&b->header);
+	values = b->header.values->values;
 
-	if (!git_strmap_valid_index(b->values, pos)) {
-		giterr_set(GITERR_CONFIG, "Could not find key '%s' to delete", name);
+	pos = git_strmap_lookup_index(values, key);
+
+	if (!git_strmap_valid_index(values, pos)) {
+		refcounted_strmap_free(map);
 		git__free(key);
+		giterr_set(GITERR_CONFIG, "Could not find key '%s' to delete", name);
 		return GIT_ENOTFOUND;
 	}
 
-	var = git_strmap_value_at(b->values, pos);
+	refcounted_strmap_free(map);
 
 	result = regcomp(&preg, regexp, REG_EXTENDED);
 	if (result < 0) {
-		git__free(key);
 		giterr_set_regex(&preg, result);
-		regfree(&preg);
-		return -1;
+		result = -1;
+		goto out;
 	}
 
-	to_delete = git__calloc(cvar_length(var), sizeof(cvar_t *));
-	GITERR_CHECK_ALLOC(to_delete);
-	to_delete_idx = 0;
+	if ((result = config_write(b, key, &preg, NULL)) < 0)
+		goto out;
 
-	while (var != NULL) {
-		cvar_t *next = var->next;
-
-		if (regexec(&preg, var->entry->value, 0, NULL, 0) == 0) {
-			// If we are past the head, reattach previous node to next one,
-			// otherwise set the new head for the strmap.
-			if (prev != NULL) {
-				prev->next = next;
-			} else {
-				new_head = next;
-			}
-
-			to_delete[to_delete_idx++] = var;
-		} else {
-			prev = var;
-		}
-
-		var = next;
-	}
-
-	if (new_head != NULL) {
-		git_strmap_set_value_at(b->values, pos, new_head);
-	} else {
-		git_strmap_delete_at(b->values, pos);
-	}
-
-	if (to_delete_idx > 0)
-		result = config_write(b, key, &preg, NULL);
-
-	while (to_delete_idx-- > 0)
-		cvar_free(to_delete[to_delete_idx]);
+	result = config_refresh(cfg);
 
+out:
 	git__free(key);
-	git__free(to_delete);
 	regfree(&preg);
 	return result;
 }
 
+static int config_snapshot(git_config_backend **out, git_config_backend *in)
+{
+	diskfile_backend *b = (diskfile_backend *) in;
+
+	return git_config_file__snapshot(out, b);
+}
+
 int git_config_file__ondisk(git_config_backend **out, const char *path)
 {
 	diskfile_backend *backend;
@@ -621,20 +686,119 @@ int git_config_file__ondisk(git_config_backend **out, const char *path)
 	backend = git__calloc(1, sizeof(diskfile_backend));
 	GITERR_CHECK_ALLOC(backend);
 
-	backend->parent.version = GIT_CONFIG_BACKEND_VERSION;
+	backend->header.parent.version = GIT_CONFIG_BACKEND_VERSION;
 
 	backend->file_path = git__strdup(path);
 	GITERR_CHECK_ALLOC(backend->file_path);
 
-	backend->parent.open = config_open;
-	backend->parent.get = config_get;
-	backend->parent.set = config_set;
-	backend->parent.set_multivar = config_set_multivar;
-	backend->parent.del = config_delete;
-	backend->parent.del_multivar = config_delete_multivar;
-	backend->parent.iterator = config_iterator_new;
-	backend->parent.refresh = config_refresh;
-	backend->parent.free = backend_free;
+	backend->header.parent.open = config_open;
+	backend->header.parent.get = config_get;
+	backend->header.parent.set = config_set;
+	backend->header.parent.set_multivar = config_set_multivar;
+	backend->header.parent.del = config_delete;
+	backend->header.parent.del_multivar = config_delete_multivar;
+	backend->header.parent.iterator = config_iterator_new;
+	backend->header.parent.refresh = config_refresh;
+	backend->header.parent.snapshot = config_snapshot;
+	backend->header.parent.free = backend_free;
+
+	*out = (git_config_backend *)backend;
+
+	return 0;
+}
+
+static int config_set_readonly(git_config_backend *cfg, const char *name, const char *value)
+{
+	GIT_UNUSED(cfg);
+	GIT_UNUSED(name);
+	GIT_UNUSED(value);
+
+	return config_error_readonly();
+}
+
+static int config_set_multivar_readonly(
+	git_config_backend *cfg, const char *name, const char *regexp, const char *value)
+{
+	GIT_UNUSED(cfg);
+	GIT_UNUSED(name);
+	GIT_UNUSED(regexp);
+	GIT_UNUSED(value);
+
+	return config_error_readonly();
+}
+
+static int config_delete_multivar_readonly(git_config_backend *cfg, const char *name, const char *regexp)
+{
+	GIT_UNUSED(cfg);
+	GIT_UNUSED(name);
+	GIT_UNUSED(regexp);
+
+	return config_error_readonly();
+}
+
+static int config_delete_readonly(git_config_backend *cfg, const char *name)
+{
+	GIT_UNUSED(cfg);
+	GIT_UNUSED(name);
+
+	return config_error_readonly();
+}
+
+static int config_refresh_readonly(git_config_backend *cfg)
+{
+	GIT_UNUSED(cfg);
+
+	return config_error_readonly();
+}
+
+static void backend_readonly_free(git_config_backend *_backend)
+{
+	diskfile_backend *backend = (diskfile_backend *)_backend;
+
+	if (backend == NULL)
+		return;
+
+	refcounted_strmap_free(backend->header.values);
+	git__free(backend);
+}
+
+static int config_readonly_open(git_config_backend *cfg, git_config_level_t level)
+{
+	diskfile_readonly_backend *b = (diskfile_readonly_backend *) cfg;
+	diskfile_backend *src = b->snapshot_from;
+	refcounted_strmap *src_map;
+
+	/* We're just copying data, don't care about the level */
+	GIT_UNUSED(level);
+
+	src_map = refcounted_strmap_take(&src->header);
+	b->header.values = src_map;
+
+	return 0;
+}
+
+int git_config_file__snapshot(git_config_backend **out, diskfile_backend *in)
+{
+	diskfile_readonly_backend *backend;
+
+	backend = git__calloc(1, sizeof(diskfile_readonly_backend));
+	GITERR_CHECK_ALLOC(backend);
+
+	backend->header.parent.version = GIT_CONFIG_BACKEND_VERSION;
+
+	backend->snapshot_from = in;
+
+	backend->header.readonly = 1;
+	backend->header.parent.version = GIT_CONFIG_BACKEND_VERSION;
+	backend->header.parent.open = config_readonly_open;
+	backend->header.parent.get = config_get;
+	backend->header.parent.set = config_set_readonly;
+	backend->header.parent.set_multivar = config_set_multivar_readonly;
+	backend->header.parent.del = config_delete_readonly;
+	backend->header.parent.del_multivar = config_delete_multivar_readonly;
+	backend->header.parent.iterator = config_iterator_new;
+	backend->header.parent.refresh = config_refresh_readonly;
+	backend->header.parent.free = backend_readonly_free;
 
 	*out = (git_config_backend *)backend;
 
@@ -1014,16 +1178,15 @@ static int included_path(git_buf *out, const char *dir, const char *path)
 	return git_path_join_unrooted(out, path, dir, NULL);
 }
 
-static int config_parse(diskfile_backend *cfg_file, struct reader *reader, git_config_level_t level, int depth)
+static int config_parse(git_strmap *values, diskfile_backend *cfg_file, struct reader *reader, git_config_level_t level, int depth)
 {
 	int c;
 	char *current_section = NULL;
 	char *var_name;
 	char *var_value;
-	cvar_t *var, *existing;
+	cvar_t *var;
 	git_buf buf = GIT_BUF_INIT;
 	int result = 0;
-	khiter_t pos;
 	uint32_t reader_idx;
 
 	if (depth >= MAX_INCLUDE_DEPTH) {
@@ -1088,21 +1251,13 @@ static int config_parse(diskfile_backend *cfg_file, struct reader *reader, git_c
 			var->entry->level = level;
 			var->included = !!depth;
 
-			/* Add or append the new config option */
-			pos = git_strmap_lookup_index(cfg_file->values, var->entry->name);
-			if (!git_strmap_valid_index(cfg_file->values, pos)) {
-				git_strmap_insert(cfg_file->values, var->entry->name, var, result);
-				if (result < 0)
-					break;
+
+			if ((result = append_entry(values, var)) < 0)
+				break;
+			else
 				result = 0;
-			} else {
-				existing = git_strmap_value_at(cfg_file->values, pos);
-				while (existing->next != NULL) {
-					existing = existing->next;
-				}
-				existing->next = var;
-			}
 
+			/* Add or append the new config option */
 			if (!git__strcmp(var->entry->name, "include.path")) {
 				struct reader *r;
 				git_buf path = GIT_BUF_INIT;
@@ -1131,7 +1286,7 @@ static int config_parse(diskfile_backend *cfg_file, struct reader *reader, git_c
 									    &r->file_size, NULL)) < 0)
 					break;
 
-				result = config_parse(cfg_file, r, level, depth+1);
+				result = config_parse(values, cfg_file, r, level, depth+1);
 				r = git_array_get(cfg_file->readers, index);
 				git_buf_free(&r->buffer);
 
@@ -1374,7 +1529,7 @@ static int config_write(diskfile_backend *cfg, const char *key, const regex_t *p
 			 * this, but instead we'll handle it gracefully with an error. */
 			if (value == NULL) {
 				giterr_set(GITERR_CONFIG,
-					"Race condition when writing a config file (a cvar has been removed)");
+					"race condition when writing a config file (a cvar has been removed)");
 				goto rewrite_fail;
 			}
 
diff --git a/src/diff_driver.c b/src/diff_driver.c
index 8136e0dd9..28c0a6b17 100644
--- a/src/diff_driver.c
+++ b/src/diff_driver.c
@@ -219,7 +219,7 @@ static int git_diff_driver_load(
 	git_diff_driver *drv = NULL;
 	size_t namelen = strlen(driver_name);
 	khiter_t pos;
-	git_config *cfg;
+	git_config *cfg, *repo_cfg;
 	git_buf name = GIT_BUF_INIT;
 	const git_config_entry *ce;
 	bool found_driver = false;
@@ -234,7 +234,7 @@ static int git_diff_driver_load(
 	}
 
 	/* if you can't read config for repo, just use default driver */
-	if (git_repository_config__weakptr(&cfg, repo) < 0) {
+	if (git_repository_config_snapshot(&cfg, repo) < 0) {
 		giterr_clear();
 		goto done;
 	}
@@ -321,6 +321,7 @@ static int git_diff_driver_load(
 
 done:
 	git_buf_free(&name);
+	git_config_free(cfg);
 
 	if (!*out) {
 		int error2 = git_diff_driver_builtin(out, reg, driver_name);
diff --git a/src/pack-objects.c b/src/pack-objects.c
index ace8afd17..8b6acee15 100644
--- a/src/pack-objects.c
+++ b/src/pack-objects.c
@@ -90,8 +90,8 @@ static int packbuilder_config(git_packbuilder *pb)
 	int ret;
 	int64_t val;
 
-	if (git_repository_config__weakptr(&config, pb->repo) < 0)
-		return -1;
+	if ((ret = git_repository_config_snapshot(&config, pb->repo)) < 0)
+		return ret;
 
 #define config_get(KEY,DST,DFLT) do { \
 	ret = git_config_get_int64(&val, config, KEY); \
@@ -109,6 +109,8 @@ static int packbuilder_config(git_packbuilder *pb)
 
 #undef config_get
 
+	git_config_free(config);
+
 	return 0;
 }
 
diff --git a/src/remote.c b/src/remote.c
index 8f302a51e..31ee97795 100644
--- a/src/remote.c
+++ b/src/remote.c
@@ -356,8 +356,8 @@ int git_remote_load(git_remote **out, git_repository *repo, const char *name)
 	if ((error = ensure_remote_name_is_valid(name)) < 0)
 		return error;
 
-	if (git_repository_config__weakptr(&config, repo) < 0)
-		return -1;
+	if ((error = git_repository_config_snapshot(&config, repo)) < 0)
+		return error;
 
 	remote = git__malloc(sizeof(git_remote));
 	GITERR_CHECK_ALLOC(remote);
@@ -437,6 +437,7 @@ int git_remote_load(git_remote **out, git_repository *repo, const char *name)
 	*out = remote;
 
 cleanup:
+	git_config_free(config);
 	git_buf_free(&buf);
 
 	if (error < 0)
diff --git a/src/repository.c b/src/repository.c
index df5f322ce..87f6f7ab7 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -169,13 +169,9 @@ int git_repository_new(git_repository **out)
 	return 0;
 }
 
-static int load_config_data(git_repository *repo)
+static int load_config_data(git_repository *repo, const git_config *config)
 {
 	int is_bare;
-	git_config *config;
-
-	if (git_repository_config__weakptr(&config, repo) < 0)
-		return -1;
 
 	/* Try to figure out if it's bare, default to non-bare if it's not set */
 	if (git_config_get_bool(&is_bare, config, "core.bare") < 0)
@@ -186,19 +182,15 @@ static int load_config_data(git_repository *repo)
 	return 0;
 }
 
-static int load_workdir(git_repository *repo, git_buf *parent_path)
+static int load_workdir(git_repository *repo, git_config *config, git_buf *parent_path)
 {
 	int         error;
-	git_config *config;
 	const git_config_entry *ce;
 	git_buf     worktree = GIT_BUF_INIT;
 
 	if (repo->is_bare)
 		return 0;
 
-	if ((error = git_repository_config__weakptr(&config, repo)) < 0)
-		return error;
-
 	if ((error = git_config__lookup_entry(
 			&ce, config, "core.worktree", false)) < 0)
 		return error;
@@ -451,6 +443,7 @@ int git_repository_open_ext(
 	int error;
 	git_buf path = GIT_BUF_INIT, parent = GIT_BUF_INIT;
 	git_repository *repo;
+	git_config *config;
 
 	if (repo_ptr)
 		*repo_ptr = NULL;
@@ -465,15 +458,20 @@ int git_repository_open_ext(
 	repo->path_repository = git_buf_detach(&path);
 	GITERR_CHECK_ALLOC(repo->path_repository);
 
+	if ((error = git_repository_config_snapshot(&config, repo)) < 0)
+		return error;
+
 	if ((flags & GIT_REPOSITORY_OPEN_BARE) != 0)
 		repo->is_bare = 1;
-	else if ((error = load_config_data(repo)) < 0 ||
-		(error = load_workdir(repo, &parent)) < 0)
+	else if ((error = load_config_data(repo, config)) < 0 ||
+		 (error = load_workdir(repo, config, &parent)) < 0)
 	{
+		git_config_free(config);
 		git_repository_free(repo);
 		return error;
 	}
 
+	git_config_free(config);
 	git_buf_free(&parent);
 	*repo_ptr = repo;
 	return 0;
@@ -627,6 +625,16 @@ int git_repository_config(git_config **out, git_repository *repo)
 	return 0;
 }
 
+int git_repository_config_snapshot(git_config **out, git_repository *repo)
+{
+	git_config *weak;
+
+	if (git_repository_config__weakptr(&weak, repo) < 0)
+		return -1;
+
+	return git_config_snapshot(out, weak);
+}
+
 void git_repository_set_config(git_repository *repo, git_config *config)
 {
 	assert(repo && config);
diff --git a/src/signature.c b/src/signature.c
index f501cd8b6..2545b7519 100644
--- a/src/signature.c
+++ b/src/signature.c
@@ -144,7 +144,7 @@ int git_signature_default(git_signature **out, git_repository *repo)
 	git_config *cfg;
 	const char *user_name, *user_email;
 
-	if ((error = git_repository_config(&cfg, repo)) < 0)
+	if ((error = git_repository_config_snapshot(&cfg, repo)) < 0)
 		return error;
 
 	if (!(error = git_config_get_string(&user_name, cfg, "user.name")) &&
diff --git a/tests/config/multivar.c b/tests/config/multivar.c
index afdb1e5f4..015008992 100644
--- a/tests/config/multivar.c
+++ b/tests/config/multivar.c
@@ -231,13 +231,13 @@ void test_config_multivar__delete(void)
 
 	n = 0;
 	cl_git_pass(git_config_get_multivar_foreach(cfg, _name, NULL, cb, &n));
-	cl_assert(n == 2);
+	cl_assert_equal_i(2, n);
 
 	cl_git_pass(git_config_delete_multivar(cfg, _name, "github"));
 
 	n = 0;
 	cl_git_pass(git_config_get_multivar_foreach(cfg, _name, NULL, cb, &n));
-	cl_assert(n == 1);
+	cl_assert_equal_i(1, n);
 
 	git_config_free(cfg);
 
@@ -245,7 +245,7 @@ void test_config_multivar__delete(void)
 
 	n = 0;
 	cl_git_pass(git_config_get_multivar_foreach(cfg, _name, NULL, cb, &n));
-	cl_assert(n == 1);
+	cl_assert_equal_i(1, n);
 
 	git_config_free(cfg);
 }
diff --git a/tests/config/refresh.c b/tests/config/refresh.c
index 99d677f0e..08cd45b95 100644
--- a/tests/config/refresh.c
+++ b/tests/config/refresh.c
@@ -26,9 +26,6 @@ void test_config_refresh__update_value(void)
 
 	cl_git_rewritefile(TEST_FILE, "[section]\n\tvalue = 10\n\n");
 
-	cl_git_pass(git_config_get_int32(&v, cfg, "section.value"));
-	cl_assert_equal_i(1, v);
-
 	cl_git_pass(git_config_refresh(cfg));
 
 	cl_git_pass(git_config_get_int32(&v, cfg, "section.value"));
@@ -53,9 +50,9 @@ void test_config_refresh__delete_value(void)
 
 	cl_git_rewritefile(TEST_FILE, "[section]\n\tnewval = 10\n\n");
 
-	cl_git_pass(git_config_get_int32(&v, cfg, "section.value"));
-	cl_assert_equal_i(1, v);
-	cl_git_fail(git_config_get_int32(&v, cfg, "section.newval"));
+	cl_git_fail_with(GIT_ENOTFOUND, git_config_get_int32(&v, cfg, "section.value"));
+
+	cl_git_pass(git_config_get_int32(&v, cfg, "section.newval"));
 
 	cl_git_pass(git_config_refresh(cfg));
 
diff --git a/tests/config/snapshot.c b/tests/config/snapshot.c
new file mode 100644
index 000000000..c9f15921a
--- /dev/null
+++ b/tests/config/snapshot.c
@@ -0,0 +1,64 @@
+#include "clar_libgit2.h"
+
+void test_config_snapshot__create_snapshot(void)
+{
+	int32_t tmp;
+	git_config *cfg, *snapshot;
+	const char *filename = "config-ext-change";
+
+	cl_git_mkfile(filename, "[old]\nvalue = 5\n");
+
+	cl_git_pass(git_config_open_ondisk(&cfg, filename));
+
+	cl_git_pass(git_config_get_int32(&tmp, cfg, "old.value"));
+	cl_assert_equal_i(5, tmp);
+
+	cl_git_pass(git_config_snapshot(&snapshot, cfg));
+
+	/* Change the value on the file itself (simulate external process) */
+	cl_git_mkfile(filename, "[old]\nvalue = 56\n");
+
+	cl_git_pass(git_config_get_int32(&tmp, cfg, "old.value"));
+	cl_assert_equal_i(56, tmp);
+
+	cl_git_pass(git_config_get_int32(&tmp, snapshot, "old.value"));
+	cl_assert_equal_i(5, tmp);
+	
+	git_config_free(snapshot);
+	git_config_free(cfg);
+}
+
+static int count_me(const git_config_entry *entry, void *payload)
+{
+	int *n = (int *) payload;
+
+	GIT_UNUSED(entry);
+
+	(*n)++;
+
+	return 0;
+}
+
+void test_config_snapshot__multivar(void)
+{
+	int count = 0;
+	git_config *cfg, *snapshot;
+	const char *filename = "config-file";
+
+	cl_git_mkfile(filename, "[old]\nvalue = 5\nvalue = 6\n");
+
+	cl_git_pass(git_config_open_ondisk(&cfg, filename));
+	cl_git_pass(git_config_get_multivar_foreach(cfg, "old.value", NULL, count_me, &count));
+
+	cl_assert_equal_i(2, count);
+
+	cl_git_pass(git_config_snapshot(&snapshot, cfg));
+	git_config_free(cfg);
+
+	count = 0;
+	cl_git_pass(git_config_get_multivar_foreach(snapshot, "old.value", NULL, count_me, &count));
+
+	cl_assert_equal_i(2, count);
+
+	git_config_free(snapshot);
+}
diff --git a/tests/config/write.c b/tests/config/write.c
index 922d75557..402be9317 100644
--- a/tests/config/write.c
+++ b/tests/config/write.c
@@ -304,3 +304,30 @@ void test_config_write__updating_a_locked_config_file_returns_ELOCKED(void)
 	git_config_free(cfg);
 }
 
+void test_config_write__outside_change(void)
+{
+	int32_t tmp;
+	git_config *cfg;
+	const char *filename = "config-ext-change";
+
+	cl_git_mkfile(filename, "[old]\nvalue = 5\n");
+
+	cl_git_pass(git_config_open_ondisk(&cfg, filename));
+
+	cl_git_pass(git_config_get_int32(&tmp, cfg, "old.value"));
+
+	/* Change the value on the file itself (simulate external process) */
+	cl_git_mkfile(filename, "[old]\nvalue = 6\n");
+
+	cl_git_pass(git_config_set_int32(cfg, "new.value", 7));
+
+	cl_git_pass(git_config_get_int32(&tmp, cfg, "old.value"));
+	cl_assert_equal_i(6, tmp);
+
+	cl_git_pass(git_config_refresh(cfg));
+
+	cl_git_pass(git_config_get_int32(&tmp, cfg, "old.value"));
+	cl_assert_equal_i(6, tmp);
+
+	git_config_free(cfg);
+}