Merge pull request #5186 from pks-t/pks/config-snapshot-separation

config: separate file and snapshot backends

5 files changed, 337 insertions, 233 deletions

diff --git a/src/config_backend.h b/src/config_backend.h
index 6d678ae43..dbb190514 100644
--- a/src/config_backend.h
+++ b/src/config_backend.h
@@ -26,6 +26,18 @@
 extern int git_config_backend_from_file(git_config_backend **out, const char *path);
 
 /**
+ * Create a readonly configuration file backend from another backend
+ *
+ * This copies the complete contents of the source backend to the
+ * new backend. The new backend will be completely read-only and
+ * cannot be modified.
+ *
+ * @param out the new snapshotted backend
+ * @param source the backend to copy
+ */
+extern int git_config_backend_snapshot(git_config_backend **out, git_config_backend *source);
+
+/**
  * Create an in-memory configuration file backend
  *
  * @param out the new backend
diff --git a/src/config_entries.c b/src/config_entries.c
index 18f8b21ff..2eb9e666c 100644
--- a/src/config_entries.c
+++ b/src/config_entries.c
@@ -67,6 +67,36 @@ int git_config_entries_new(git_config_entries **out)
 	return error;
 }
 
+int git_config_entries_dup_entry(git_config_entries *entries, const git_config_entry *entry)
+{
+	git_config_entry *duplicated;
+	int error;
+
+	duplicated = git__calloc(1, sizeof(git_config_entry));
+	GIT_ERROR_CHECK_ALLOC(duplicated);
+
+	duplicated->name = git__strdup(entry->name);
+	GIT_ERROR_CHECK_ALLOC(duplicated->name);
+
+	if (entry->value) {
+		duplicated->value = git__strdup(entry->value);
+		GIT_ERROR_CHECK_ALLOC(duplicated->value);
+	}
+	duplicated->level = entry->level;
+	duplicated->include_depth = entry->include_depth;
+
+	if ((error = git_config_entries_append(entries, duplicated)) < 0)
+		goto out;
+
+out:
+	if (error && duplicated) {
+		git__free((char *) duplicated->name);
+		git__free((char *) duplicated->value);
+		git__free(duplicated);
+	}
+	return error;
+}
+
 int git_config_entries_dup(git_config_entries **out, git_config_entries *entries)
 {
 	git_config_entries *result = NULL;
@@ -76,22 +106,9 @@ int git_config_entries_dup(git_config_entries **out, git_config_entries *entries
 	if ((error = git_config_entries_new(&result)) < 0)
 		goto out;
 
-	for (head = entries->list; head; head = head->next) {
-		git_config_entry *dup;
-
-		dup = git__calloc(1, sizeof(git_config_entry));
-		dup->name = git__strdup(head->entry->name);
-		GIT_ERROR_CHECK_ALLOC(dup->name);
-		if (head->entry->value) {
-			dup->value = git__strdup(head->entry->value);
-			GIT_ERROR_CHECK_ALLOC(dup->value);
-		}
-		dup->level = head->entry->level;
-		dup->include_depth = head->entry->include_depth;
-
-		if ((error = git_config_entries_append(result, dup)) < 0)
+	for (head = entries->list; head; head = head->next)
+		if ((git_config_entries_dup_entry(result, head->entry)) < 0)
 			goto out;
-	}
 
 	*out = result;
 	result = NULL;
diff --git a/src/config_entries.h b/src/config_entries.h
index 6fdbc41ba..832379e74 100644
--- a/src/config_entries.h
+++ b/src/config_entries.h
@@ -14,6 +14,7 @@ typedef struct git_config_entries git_config_entries;
 
 int git_config_entries_new(git_config_entries **out);
 int git_config_entries_dup(git_config_entries **out, git_config_entries *entries);
+int git_config_entries_dup_entry(git_config_entries *entries, const git_config_entry *entry);
 void git_config_entries_incref(git_config_entries *entries);
 void git_config_entries_free(git_config_entries *entries);
 /* Add or append the new config option */
diff --git a/src/config_file.c b/src/config_file.c
index 88bba90a7..3e8e30cbd 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -7,17 +7,19 @@
 
 #include "config.h"
 
-#include "filebuf.h"
-#include "sysdir.h"
-#include "buffer.h"
-#include "buf_text.h"
 #include "git2/config.h"
 #include "git2/sys/config.h"
 #include "git2/types.h"
-#include "strmap.h"
+
 #include "array.h"
-#include "config_parse.h"
+#include "buf_text.h"
+#include "buffer.h"
+#include "config_backend.h"
 #include "config_entries.h"
+#include "config_parse.h"
+#include "filebuf.h"
+#include "strmap.h"
+#include "sysdir.h"
 #include "wildmatch.h"
 
 #include <ctype.h>
@@ -26,24 +28,19 @@
 /* Max depth for [include] directives */
 #define MAX_INCLUDE_DEPTH 10
 
-typedef struct diskfile {
+typedef struct config_file {
 	git_futils_filestamp stamp;
 	git_oid checksum;
 	char *path;
-	git_array_t(struct diskfile) includes;
-} diskfile;
+	git_array_t(struct config_file) includes;
+} config_file;
 
 typedef struct {
 	git_config_backend parent;
-	/* mutex to coordinate accessing the values */
 	git_mutex values_mutex;
 	git_config_entries *entries;
 	const git_repository *repo;
 	git_config_level_t level;
-} diskfile_header;
-
-typedef struct {
-	diskfile_header header;
 
 	git_array_t(git_config_parser) readers;
 
@@ -51,61 +48,47 @@ typedef struct {
 	git_filebuf locked_buf;
 	git_buf locked_content;
 
-	diskfile file;
-} diskfile_backend;
-
-typedef struct {
-	diskfile_header header;
-
-	diskfile_backend *snapshot_from;
-} diskfile_readonly_backend;
+	config_file file;
+} config_file_backend;
 
 typedef struct {
 	const git_repository *repo;
-	diskfile *file;
+	config_file *file;
 	git_config_entries *entries;
 	git_config_level_t level;
 	unsigned int depth;
-} diskfile_parse_state;
+} config_file_parse_data;
 
-static int config_read(git_config_entries *entries, const git_repository *repo, diskfile *file, git_config_level_t level, int depth);
-static int config_read_buffer(git_config_entries *entries, const git_repository *repo, diskfile *file, git_config_level_t level, int depth, const char *buf, size_t buflen);
-static int config_write(diskfile_backend *cfg, const char *orig_key, const char *key, const p_regex_t *preg, const char *value);
+static int config_read(git_config_entries *entries, const git_repository *repo, config_file *file, git_config_level_t level, int depth);
+static int config_read_buffer(git_config_entries *entries, const git_repository *repo, config_file *file, git_config_level_t level, int depth, const char *buf, size_t buflen);
+static int config_write(config_file_backend *cfg, const char *orig_key, const char *key, const p_regex_t *preg, const char *value);
 static char *escape_value(const char *ptr);
 
-static int config_snapshot(git_config_backend **out, git_config_backend *in);
-
-static int config_error_readonly(void)
-{
-	git_error_set(GIT_ERROR_CONFIG, "this backend is read-only");
-	return -1;
-}
-
 /**
  * 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 git_config_entries *diskfile_entries_take(diskfile_header *h)
+static git_config_entries *diskfile_entries_take(config_file_backend *b)
 {
 	git_config_entries *entries;
 
-	if (git_mutex_lock(&h->values_mutex) < 0) {
+	if (git_mutex_lock(&b->values_mutex) < 0) {
 	    git_error_set(GIT_ERROR_OS, "failed to lock config backend");
 	    return NULL;
 	}
 
-	entries = h->entries;
+	entries = b->entries;
 	git_config_entries_incref(entries);
 
-	git_mutex_unlock(&h->values_mutex);
+	git_mutex_unlock(&b->values_mutex);
 
 	return entries;
 }
 
-static void config_file_clear(diskfile *file)
+static void config_file_clear(config_file *file)
 {
-	diskfile *include;
+	config_file *include;
 	uint32_t i;
 
 	if (file == NULL)
@@ -121,29 +104,29 @@ static void config_file_clear(diskfile *file)
 
 static int config_open(git_config_backend *cfg, git_config_level_t level, const git_repository *repo)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	int res;
 
-	b->header.level = level;
-	b->header.repo = repo;
+	b->level = level;
+	b->repo = repo;
 
-	if ((res = git_config_entries_new(&b->header.entries)) < 0)
+	if ((res = git_config_entries_new(&b->entries)) < 0)
 		return res;
 
 	if (!git_path_exists(b->file.path))
 		return 0;
 
-	if (res < 0 || (res = config_read(b->header.entries, repo, &b->file, level, 0)) < 0) {
-		git_config_entries_free(b->header.entries);
-		b->header.entries = NULL;
+	if (res < 0 || (res = config_read(b->entries, repo, &b->file, level, 0)) < 0) {
+		git_config_entries_free(b->entries);
+		b->entries = NULL;
 	}
 
 	return res;
 }
 
-static int config_is_modified(int *modified, diskfile *file)
+static int config_is_modified(int *modified, config_file *file)
 {
-	diskfile *include;
+	config_file *include;
 	git_buf buf = GIT_BUF_INIT;
 	git_oid hash;
 	uint32_t i;
@@ -179,28 +162,30 @@ out:
 
 static int config_set_entries(git_config_backend *cfg, git_config_entries *entries)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *old = NULL;
-	diskfile *include;
+	config_file *include;
 	int error;
 	uint32_t i;
 
-	if (b->header.parent.readonly)
-		return config_error_readonly();
+	if (b->parent.readonly) {
+		git_error_set(GIT_ERROR_CONFIG, "this backend is read-only");
+		return -1;
+	}
 
 	git_array_foreach(b->file.includes, i, include)
 		config_file_clear(include);
 	git_array_clear(b->file.includes);
 
-	if ((error = git_mutex_lock(&b->header.values_mutex)) < 0) {
+	if ((error = git_mutex_lock(&b->values_mutex)) < 0) {
 		git_error_set(GIT_ERROR_OS, "failed to lock config backend");
 		goto out;
 	}
 
-	old = b->header.entries;
-	b->header.entries = entries;
+	old = b->entries;
+	b->entries = entries;
 
-	git_mutex_unlock(&b->header.values_mutex);
+	git_mutex_unlock(&b->values_mutex);
 
 out:
 	git_config_entries_free(old);
@@ -209,13 +194,13 @@ out:
 
 static int config_refresh_from_buffer(git_config_backend *cfg, const char *buf, size_t buflen)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	int error;
 
 	if ((error = git_config_entries_new(&entries)) < 0 ||
-	    (error = config_read_buffer(entries, b->header.repo, &b->file,
-					b->header.level, 0, buf, buflen)) < 0 ||
+	    (error = config_read_buffer(entries, b->repo, &b->file,
+					b->level, 0, buf, buflen)) < 0 ||
 	    (error = config_set_entries(cfg, entries)) < 0)
 		goto out;
 
@@ -227,7 +212,7 @@ out:
 
 static int config_refresh(git_config_backend *cfg)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	int error, modified;
 
@@ -241,7 +226,7 @@ static int config_refresh(git_config_backend *cfg)
 		return 0;
 
 	if ((error = git_config_entries_new(&entries)) < 0 ||
-	    (error = config_read(entries, b->header.repo, &b->file, b->header.level, 0)) < 0 ||
+	    (error = config_read(entries, b->repo, &b->file, b->level, 0)) < 0 ||
 	    (error = config_set_entries(cfg, entries)) < 0)
 		goto out;
 
@@ -254,14 +239,14 @@ out:
 
 static void backend_free(git_config_backend *_backend)
 {
-	diskfile_backend *backend = GIT_CONTAINER_OF(_backend, diskfile_backend, header.parent);
+	config_file_backend *backend = GIT_CONTAINER_OF(_backend, config_file_backend, parent);
 
 	if (backend == NULL)
 		return;
 
 	config_file_clear(&backend->file);
-	git_config_entries_free(backend->header.entries);
-	git_mutex_free(&backend->header.values_mutex);
+	git_config_entries_free(backend->entries);
+	git_mutex_free(&backend->values_mutex);
 	git__free(backend);
 }
 
@@ -269,12 +254,12 @@ static int config_iterator_new(
 	git_config_iterator **iter,
 	struct git_config_backend *backend)
 {
-	diskfile_header *bh = GIT_CONTAINER_OF(backend, diskfile_header, parent);
+	config_file_backend *b = GIT_CONTAINER_OF(backend, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	int error;
 
 	if ((error = config_refresh(backend)) < 0 ||
-	    (error = git_config_entries_dup(&entries, bh->entries)) < 0 ||
+	    (error = git_config_entries_dup(&entries, b->entries)) < 0 ||
 	    (error = git_config_entries_iterator_new(iter, entries)) < 0)
 		goto out;
 
@@ -286,7 +271,7 @@ out:
 
 static int config_set(git_config_backend *cfg, const char *name, const char *value)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries;
 	git_config_entry *existing;
 	char *key, *esc_value = NULL;
@@ -295,7 +280,7 @@ static int config_set(git_config_backend *cfg, const char *name, const char *val
 	if ((error = git_config__normalize_name(name, &key)) < 0)
 		return error;
 
-	if ((entries = diskfile_entries_take(&b->header)) == NULL)
+	if ((entries = diskfile_entries_take(b)) == NULL)
 		return -1;
 
 	/* Check whether we'd be modifying an included or multivar key */
@@ -338,7 +323,7 @@ static void free_diskfile_entry(git_config_entry *entry)
  */
 static int config_get(git_config_backend *cfg, const char *key, git_config_entry **out)
 {
-	diskfile_header *h = GIT_CONTAINER_OF(cfg, diskfile_header, parent);
+	config_file_backend *h = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	git_config_entry *entry;
 	int error = 0;
@@ -364,7 +349,7 @@ static int config_get(git_config_backend *cfg, const char *key, git_config_entry
 static int config_set_multivar(
 	git_config_backend *cfg, const char *name, const char *regexp, const char *value)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	char *key;
 	p_regex_t preg;
 	int result;
@@ -394,7 +379,7 @@ out:
 
 static int config_delete(git_config_backend *cfg, const char *name)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	git_config_entry *entry;
 	char *key = NULL;
@@ -403,7 +388,7 @@ static int config_delete(git_config_backend *cfg, const char *name)
 	if ((error = git_config__normalize_name(name, &key)) < 0)
 		goto out;
 
-	if ((entries = diskfile_entries_take(&b->header)) == NULL)
+	if ((entries = diskfile_entries_take(b)) == NULL)
 		goto out;
 
 	/* Check whether we'd be modifying an included or multivar key */
@@ -424,7 +409,7 @@ out:
 
 static int config_delete_multivar(git_config_backend *cfg, const char *name, const char *regexp)
 {
-	diskfile_backend *b = GIT_CONTAINER_OF(cfg, diskfile_backend, header.parent);
+	config_file_backend *b = GIT_CONTAINER_OF(cfg, config_file_backend, parent);
 	git_config_entries *entries = NULL;
 	git_config_entry *entry = NULL;
 	p_regex_t preg = { 0 };
@@ -434,7 +419,7 @@ static int config_delete_multivar(git_config_backend *cfg, const char *name, con
 	if ((result = git_config__normalize_name(name, &key)) < 0)
 		goto out;
 
-	if ((entries = diskfile_entries_take(&b->header)) == NULL) {
+	if ((entries = diskfile_entries_take(b)) == NULL) {
 		result = -1;
 		goto out;
 	}
@@ -463,7 +448,7 @@ out:
 
 static int config_lock(git_config_backend *_cfg)
 {
-	diskfile_backend *cfg = GIT_CONTAINER_OF(_cfg, diskfile_backend, header.parent);
+	config_file_backend *cfg = GIT_CONTAINER_OF(_cfg, config_file_backend, parent);
 	int error;
 
 	if ((error = git_filebuf_open(&cfg->locked_buf, cfg->file.path, 0, GIT_CONFIG_FILE_MODE)) < 0)
@@ -482,7 +467,7 @@ static int config_lock(git_config_backend *_cfg)
 
 static int config_unlock(git_config_backend *_cfg, int success)
 {
-	diskfile_backend *cfg = GIT_CONTAINER_OF(_cfg, diskfile_backend, header.parent);
+	config_file_backend *cfg = GIT_CONTAINER_OF(_cfg, config_file_backend, parent);
 	int error = 0;
 
 	if (success) {
@@ -499,151 +484,35 @@ static int config_unlock(git_config_backend *_cfg, int success)
 
 int git_config_backend_from_file(git_config_backend **out, const char *path)
 {
-	diskfile_backend *backend;
+	config_file_backend *backend;
 
-	backend = git__calloc(1, sizeof(diskfile_backend));
+	backend = git__calloc(1, sizeof(config_file_backend));
 	GIT_ERROR_CHECK_ALLOC(backend);
 
-	backend->header.parent.version = GIT_CONFIG_BACKEND_VERSION;
-	git_mutex_init(&backend->header.values_mutex);
+	backend->parent.version = GIT_CONFIG_BACKEND_VERSION;
+	git_mutex_init(&backend->values_mutex);
 
 	backend->file.path = git__strdup(path);
 	GIT_ERROR_CHECK_ALLOC(backend->file.path);
 	git_array_init(backend->file.includes);
 
-	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.snapshot = config_snapshot;
-	backend->header.parent.lock = config_lock;
-	backend->header.parent.unlock = config_unlock;
-	backend->header.parent.free = backend_free;
+	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.snapshot = git_config_backend_snapshot;
+	backend->parent.lock = config_lock;
+	backend->parent.unlock = config_unlock;
+	backend->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_lock_readonly(git_config_backend *_cfg)
-{
-	GIT_UNUSED(_cfg);
-
-	return config_error_readonly();
-}
-
-static int config_unlock_readonly(git_config_backend *_cfg, int success)
-{
-	GIT_UNUSED(_cfg);
-	GIT_UNUSED(success);
-
-	return config_error_readonly();
-}
-
-static void backend_readonly_free(git_config_backend *_backend)
-{
-	diskfile_backend *backend = GIT_CONTAINER_OF(_backend, diskfile_backend, header.parent);
-
-	if (backend == NULL)
-		return;
-
-	git_config_entries_free(backend->header.entries);
-	git_mutex_free(&backend->header.values_mutex);
-	git__free(backend);
-}
-
-static int config_readonly_open(git_config_backend *cfg, git_config_level_t level, const git_repository *repo)
-{
-	diskfile_readonly_backend *b = GIT_CONTAINER_OF(cfg, diskfile_readonly_backend, header.parent);
-	diskfile_backend *src = b->snapshot_from;
-	diskfile_header *src_header = &src->header;
-	git_config_entries *entries;
-	int error;
-
-	if (!src_header->parent.readonly && (error = config_refresh(&src_header->parent)) < 0)
-		return error;
-
-	/* We're just copying data, don't care about the level or repo*/
-	GIT_UNUSED(level);
-	GIT_UNUSED(repo);
-
-	if ((entries = diskfile_entries_take(src_header)) == NULL)
-		return -1;
-	b->header.entries = entries;
-
-	return 0;
-}
-
-static int config_snapshot(git_config_backend **out, git_config_backend *in)
-{
-	diskfile_readonly_backend *backend;
-
-	backend = git__calloc(1, sizeof(diskfile_readonly_backend));
-	GIT_ERROR_CHECK_ALLOC(backend);
-
-	backend->header.parent.version = GIT_CONFIG_BACKEND_VERSION;
-	git_mutex_init(&backend->header.values_mutex);
-
-	backend->snapshot_from = GIT_CONTAINER_OF(in, diskfile_backend, header.parent);
-
-	backend->header.parent.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.lock = config_lock_readonly;
-	backend->header.parent.unlock = config_unlock_readonly;
-	backend->header.parent.free = backend_readonly_free;
-
-	*out = &backend->header.parent;
-
-	return 0;
-}
-
 static int included_path(git_buf *out, const char *dir, const char *path)
 {
 	/* From the user's home */
@@ -685,9 +554,9 @@ static char *escape_value(const char *ptr)
 	return git_buf_detach(&buf);
 }
 
-static int parse_include(diskfile_parse_state *parse_data, const char *file)
+static int parse_include(config_file_parse_data *parse_data, const char *file)
 {
-	diskfile *include;
+	config_file *include;
 	git_buf path = GIT_BUF_INIT;
 	char *dir;
 	int result;
@@ -790,7 +659,7 @@ static const struct {
 	{ "gitdir/i:", conditional_match_gitdir_i }
 };
 
-static int parse_conditional_include(diskfile_parse_state *parse_data, const char *section, const char *file)
+static int parse_conditional_include(config_file_parse_data *parse_data, const char *section, const char *file)
 {
 	char *condition;
 	size_t i;
@@ -831,7 +700,7 @@ static int read_on_variable(
 	size_t line_len,
 	void *data)
 {
-	diskfile_parse_state *parse_data = (diskfile_parse_state *)data;
+	config_file_parse_data *parse_data = (config_file_parse_data *)data;
 	git_buf buf = GIT_BUF_INIT;
 	git_config_entry *entry;
 	const char *c;
@@ -881,13 +750,13 @@ static int read_on_variable(
 static int config_read_buffer(
 	git_config_entries *entries,
 	const git_repository *repo,
-	diskfile *file,
+	config_file *file,
 	git_config_level_t level,
 	int depth,
 	const char *buf,
 	size_t buflen)
 {
-	diskfile_parse_state parse_data;
+	config_file_parse_data parse_data;
 	git_config_parser reader;
 	int error;
 
@@ -921,7 +790,7 @@ out:
 static int config_read(
 	git_config_entries *entries,
 	const git_repository *repo,
-	diskfile *file,
+	config_file *file,
 	git_config_level_t level,
 	int depth)
 {
@@ -1173,7 +1042,7 @@ static int write_on_eof(
 /*
  * This is pretty much the parsing, except we write out anything we don't have
  */
-static int config_write(diskfile_backend *cfg, const char *orig_key, const char *key, const p_regex_t *preg, const char* value)
+static int config_write(config_file_backend *cfg, const char *orig_key, const char *key, const p_regex_t *preg, const char* value)
 {
 	char *orig_section = NULL, *section = NULL, *orig_name, *name, *ldot;
 	git_buf buf = GIT_BUF_INIT, contents = GIT_BUF_INIT;
@@ -1233,7 +1102,7 @@ static int config_write(diskfile_backend *cfg, const char *orig_key, const char
 		if ((error = git_filebuf_commit(&file)) < 0)
 			goto done;
 
-		if ((error = config_refresh_from_buffer(&cfg->header.parent, buf.ptr, buf.size)) < 0)
+		if ((error = config_refresh_from_buffer(&cfg->parent, buf.ptr, buf.size)) < 0)
 			goto done;
 	}
 
diff --git a/src/config_snapshot.c b/src/config_snapshot.c
new file mode 100644
index 000000000..764abe208
--- /dev/null
+++ b/src/config_snapshot.c
@@ -0,0 +1,205 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "config.h"
+
+#include "config_entries.h"
+
+typedef struct {
+	git_config_backend parent;
+	git_mutex values_mutex;
+	git_config_entries *entries;
+	git_config_backend *source;
+} config_snapshot_backend;
+
+static int config_error_readonly(void)
+{
+	git_error_set(GIT_ERROR_CONFIG, "this backend is read-only");
+	return -1;
+}
+
+static int config_iterator_new_readonly(
+	git_config_iterator **iter,
+	struct git_config_backend *backend)
+{
+	config_snapshot_backend *b = GIT_CONTAINER_OF(backend, config_snapshot_backend, parent);
+	git_config_entries *entries = NULL;
+	int error;
+
+	if ((error = git_config_entries_dup(&entries, b->entries)) < 0 ||
+	    (error = git_config_entries_iterator_new(iter, entries)) < 0)
+		goto out;
+
+out:
+	/* Let iterator delete duplicated entries when it's done */
+	git_config_entries_free(entries);
+	return error;
+}
+
+/* release the map containing the entry as an equivalent to freeing it */
+static void free_diskfile_entry(git_config_entry *entry)
+{
+	git_config_entries *entries = (git_config_entries *) entry->payload;
+	git_config_entries_free(entries);
+}
+
+static int config_get_readonly(git_config_backend *cfg, const char *key, git_config_entry **out)
+{
+	config_snapshot_backend *b = GIT_CONTAINER_OF(cfg, config_snapshot_backend, parent);
+	git_config_entries *entries = NULL;
+	git_config_entry *entry;
+	int error = 0;
+
+	if (git_mutex_lock(&b->values_mutex) < 0) {
+	    git_error_set(GIT_ERROR_OS, "failed to lock config backend");
+	    return -1;
+	}
+
+	entries = b->entries;
+	git_config_entries_incref(entries);
+	git_mutex_unlock(&b->values_mutex);
+
+	if ((error = (git_config_entries_get(&entry, entries, key))) < 0) {
+		git_config_entries_free(entries);
+		return error;
+	}
+
+	entry->free = free_diskfile_entry;
+	entry->payload = entries;
+	*out = entry;
+
+	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_lock_readonly(git_config_backend *_cfg)
+{
+	GIT_UNUSED(_cfg);
+
+	return config_error_readonly();
+}
+
+static int config_unlock_readonly(git_config_backend *_cfg, int success)
+{
+	GIT_UNUSED(_cfg);
+	GIT_UNUSED(success);
+
+	return config_error_readonly();
+}
+
+static void backend_readonly_free(git_config_backend *_backend)
+{
+	config_snapshot_backend *backend = GIT_CONTAINER_OF(_backend, config_snapshot_backend, parent);
+
+	if (backend == NULL)
+		return;
+
+	git_config_entries_free(backend->entries);
+	git_mutex_free(&backend->values_mutex);
+	git__free(backend);
+}
+
+static int config_readonly_open(git_config_backend *cfg, git_config_level_t level, const git_repository *repo)
+{
+	config_snapshot_backend *b = GIT_CONTAINER_OF(cfg, config_snapshot_backend, parent);
+	git_config_entries *entries = NULL;
+	git_config_iterator *it = NULL;
+	git_config_entry *entry;
+	int error;
+
+	/* We're just copying data, don't care about the level or repo*/
+	GIT_UNUSED(level);
+	GIT_UNUSED(repo);
+
+	if ((error = git_config_entries_new(&entries)) < 0 ||
+	    (error = b->source->iterator(&it, b->source)) < 0)
+		goto out;
+
+	while ((error = git_config_next(&entry, it)) == 0)
+		if ((error = git_config_entries_dup_entry(entries, entry)) < 0)
+			goto out;
+
+	if (error < 0) {
+		if (error != GIT_ITEROVER)
+			goto out;
+		error = 0;
+	}
+
+	b->entries = entries;
+
+out:
+	git_config_iterator_free(it);
+	if (error)
+		git_config_entries_free(entries);
+	return error;
+}
+
+int git_config_backend_snapshot(git_config_backend **out, git_config_backend *source)
+{
+	config_snapshot_backend *backend;
+
+	backend = git__calloc(1, sizeof(config_snapshot_backend));
+	GIT_ERROR_CHECK_ALLOC(backend);
+
+	backend->parent.version = GIT_CONFIG_BACKEND_VERSION;
+	git_mutex_init(&backend->values_mutex);
+
+	backend->source = source;
+
+	backend->parent.readonly = 1;
+	backend->parent.version = GIT_CONFIG_BACKEND_VERSION;
+	backend->parent.open = config_readonly_open;
+	backend->parent.get = config_get_readonly;
+	backend->parent.set = config_set_readonly;
+	backend->parent.set_multivar = config_set_multivar_readonly;
+	backend->parent.del = config_delete_readonly;
+	backend->parent.del_multivar = config_delete_multivar_readonly;
+	backend->parent.iterator = config_iterator_new_readonly;
+	backend->parent.lock = config_lock_readonly;
+	backend->parent.unlock = config_unlock_readonly;
+	backend->parent.free = backend_readonly_free;
+
+	*out = &backend->parent;
+
+	return 0;
+}