thodg/libgit2/src/refdb_fs.c

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• Hash : d00d5464
  Author :
  Date : 2013-03-01T15:37:33
  

  immutable references and a pluggable ref database

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• src/refdb_fs.c

• /*
   * 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 "refs.h"
  #include "hash.h"
  #include "repository.h"
  #include "fileops.h"
  #include "pack.h"
  #include "reflog.h"
  #include "config.h"
  #include "refdb.h"
  #include "refdb_fs.h"
  
  #include <git2/tag.h>
  #include <git2/object.h>
  #include <git2/refdb.h>
  #include <git2/refdb_backend.h>
  
  GIT__USE_STRMAP;
  
  #define DEFAULT_NESTING_LEVEL	5
  #define MAX_NESTING_LEVEL		10
  
  enum {
  	GIT_PACKREF_HAS_PEEL = 1,
  	GIT_PACKREF_WAS_LOOSE = 2
  };
  
  struct packref {
  	git_oid oid;
  	git_oid peel;
  	char flags;
  	char name[GIT_FLEX_ARRAY];
  };
  
  typedef struct refdb_fs_backend {
  	git_refdb_backend parent;
  
  	git_repository *repo;
  	const char *path;
  	git_refdb *refdb;
  
  	git_refcache refcache;
  } refdb_fs_backend;
  
  static int reference_read(
  	git_buf *file_content,
  	time_t *mtime,
  	const char *repo_path,
  	const char *ref_name,
  	int *updated)
  {
  	git_buf path = GIT_BUF_INIT;
  	int result;
  
  	assert(file_content && repo_path && ref_name);
  
  	/* Determine the full path of the file */
  	if (git_buf_joinpath(&path, repo_path, ref_name) < 0)
  		return -1;
  	
  	result = git_futils_readbuffer_updated(file_content, path.ptr, mtime, NULL, updated);
  	git_buf_free(&path);
  
  	return result;
  }
  
  static int packed_parse_oid(
  	struct packref **ref_out,
  	const char **buffer_out,
  	const char *buffer_end)
  {
  	struct packref *ref = NULL;
  
  	const char *buffer = *buffer_out;
  	const char *refname_begin, *refname_end;
  
  	size_t refname_len;
  	git_oid id;
  
  	refname_begin = (buffer + GIT_OID_HEXSZ + 1);
  	if (refname_begin >= buffer_end || refname_begin[-1] != ' ')
  		goto corrupt;
  
  	/* Is this a valid object id? */
  	if (git_oid_fromstr(&id, buffer) < 0)
  		goto corrupt;
  
  	refname_end = memchr(refname_begin, '\n', buffer_end - refname_begin);
  	if (refname_end == NULL)
  		refname_end = buffer_end;
  
  	if (refname_end[-1] == '\r')
  		refname_end--;
  
  	refname_len = refname_end - refname_begin;
  
  	ref = git__malloc(sizeof(struct packref) + refname_len + 1);
  	GITERR_CHECK_ALLOC(ref);
  
  	memcpy(ref->name, refname_begin, refname_len);
  	ref->name[refname_len] = 0;
  
  	git_oid_cpy(&ref->oid, &id);
  
  	ref->flags = 0;
  
  	*ref_out = ref;
  	*buffer_out = refname_end + 1;
  
  	return 0;
  
  corrupt:
  	git__free(ref);
  	giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
  	return -1;
  }
  
  static int packed_parse_peel(
  	struct packref *tag_ref,
  	const char **buffer_out,
  	const char *buffer_end)
  {
  	const char *buffer = *buffer_out + 1;
  
  	assert(buffer[-1] == '^');
  
  	/* Ensure it's not the first entry of the file */
  	if (tag_ref == NULL)
  		goto corrupt;
  
  	/* Ensure reference is a tag */
  	if (git__prefixcmp(tag_ref->name, GIT_REFS_TAGS_DIR) != 0)
  		goto corrupt;
  
  	if (buffer + GIT_OID_HEXSZ > buffer_end)
  		goto corrupt;
  
  	/* Is this a valid object id? */
  	if (git_oid_fromstr(&tag_ref->peel, buffer) < 0)
  		goto corrupt;
  
  	buffer = buffer + GIT_OID_HEXSZ;
  	if (*buffer == '\r')
  		buffer++;
  
  	if (buffer != buffer_end) {
  		if (*buffer == '\n')
  			buffer++;
  		else
  			goto corrupt;
  	}
  
  	*buffer_out = buffer;
  	return 0;
  
  corrupt:
  	giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
  	return -1;
  }
  
  static int packed_load(refdb_fs_backend *backend)
  {
  	int result, updated;
  	git_buf packfile = GIT_BUF_INIT;
  	const char *buffer_start, *buffer_end;
  	git_refcache *ref_cache = &backend->refcache;
  
  	/* First we make sure we have allocated the hash table */
  	if (ref_cache->packfile == NULL) {
  		ref_cache->packfile = git_strmap_alloc();
  		GITERR_CHECK_ALLOC(ref_cache->packfile);
  	}
  	
  	result = reference_read(&packfile, &ref_cache->packfile_time,
  		backend->path, GIT_PACKEDREFS_FILE, &updated);
  
  	/*
  	 * If we couldn't find the file, we need to clear the table and
  	 * return. On any other error, we return that error. If everything
  	 * went fine and the file wasn't updated, then there's nothing new
  	 * for us here, so just return. Anything else means we need to
  	 * refresh the packed refs.
  	 */
  	if (result == GIT_ENOTFOUND) {
  		git_strmap_clear(ref_cache->packfile);
  		return 0;
  	}
  
  	if (result < 0)
  		return -1;
  	
  	if (!updated)
  		return 0;
  
  	/*
  	 * At this point, we want to refresh the packed refs. We already
  	 * have the contents in our buffer.
  	 */
  	git_strmap_clear(ref_cache->packfile);
  
  	buffer_start = (const char *)packfile.ptr;
  	buffer_end = (const char *)(buffer_start) + packfile.size;
  
  	while (buffer_start < buffer_end && buffer_start[0] == '#') {
  		buffer_start = strchr(buffer_start, '\n');
  		if (buffer_start == NULL)
  			goto parse_failed;
  
  		buffer_start++;
  	}
  
  	while (buffer_start < buffer_end) {
  		int err;
  		struct packref *ref = NULL;
  
  		if (packed_parse_oid(&ref, &buffer_start, buffer_end) < 0)
  			goto parse_failed;
  
  		if (buffer_start[0] == '^') {
  			if (packed_parse_peel(ref, &buffer_start, buffer_end) < 0)
  				goto parse_failed;
  		}
  
  		git_strmap_insert(ref_cache->packfile, ref->name, ref, err);
  		if (err < 0)
  			goto parse_failed;
  	}
  
  	git_buf_free(&packfile);
  	return 0;
  
  parse_failed:
  	git_strmap_free(ref_cache->packfile);
  	ref_cache->packfile = NULL;
  	git_buf_free(&packfile);
  	return -1;
  }
  
  static int loose_parse_oid(git_oid *oid, git_buf *file_content)
  {
  	size_t len;
  	const char *str;
  
  	len = git_buf_len(file_content);
  	if (len < GIT_OID_HEXSZ)
  		goto corrupted;
  
  	/* str is guranteed to be zero-terminated */
  	str = git_buf_cstr(file_content);
  
  	/* we need to get 40 OID characters from the file */
  	if (git_oid_fromstr(oid, git_buf_cstr(file_content)) < 0)
  		goto corrupted;
  
  	/* If the file is longer than 40 chars, the 41st must be a space */
  	str += GIT_OID_HEXSZ;
  	if (*str == '\0' || git__isspace(*str))
  		return 0;
  
  corrupted:
  	giterr_set(GITERR_REFERENCE, "Corrupted loose reference file");
  	return -1;
  }
  
  static int loose_lookup_to_packfile(
  	struct packref **ref_out,
  	refdb_fs_backend *backend,
  	const char *name)
  {
  	git_buf ref_file = GIT_BUF_INIT;
  	struct packref *ref = NULL;
  	size_t name_len;
  
  	*ref_out = NULL;
  
  	if (reference_read(&ref_file, NULL, backend->path, name, NULL) < 0)
  		return -1;
  
  	git_buf_rtrim(&ref_file);
  
  	name_len = strlen(name);
  	ref = git__malloc(sizeof(struct packref) + name_len + 1);
  	GITERR_CHECK_ALLOC(ref);
  
  	memcpy(ref->name, name, name_len);
  	ref->name[name_len] = 0;
  
  	if (loose_parse_oid(&ref->oid, &ref_file) < 0) {
  		git_buf_free(&ref_file);
  		git__free(ref);
  		return -1;
  	}
  
  	ref->flags = GIT_PACKREF_WAS_LOOSE;
  
  	*ref_out = ref;
  	git_buf_free(&ref_file);
  	return 0;
  }
  
  
  static int _dirent_loose_load(void *data, git_buf *full_path)
  {
  	refdb_fs_backend *backend = (refdb_fs_backend *)data;
  	void *old_ref = NULL;
  	struct packref *ref;
  	const char *file_path;
  	int err;
  
  	if (git_path_isdir(full_path->ptr) == true)
  		return git_path_direach(full_path, _dirent_loose_load, backend);
  
  	file_path = full_path->ptr + strlen(backend->path);
  
  	if (loose_lookup_to_packfile(&ref, backend, file_path) < 0)
  		return -1;
  
  	git_strmap_insert2(
  		backend->refcache.packfile, ref->name, ref, old_ref, err);
  	if (err < 0) {
  		git__free(ref);
  		return -1;
  	}
  
  	git__free(old_ref);
  	return 0;
  }
  
  /*
   * Load all the loose references from the repository
   * into the in-memory Packfile, and build a vector with
   * all the references so it can be written back to
   * disk.
   */
  static int packed_loadloose(refdb_fs_backend *backend)
  {
  	git_buf refs_path = GIT_BUF_INIT;
  	int result;
  
  	/* the packfile must have been previously loaded! */
  	assert(backend->refcache.packfile);
  
  	if (git_buf_joinpath(&refs_path, backend->path, GIT_REFS_DIR) < 0)
  		return -1;
  
  	/*
  	 * Load all the loose files from disk into the Packfile table.
  	 * This will overwrite any old packed entries with their
  	 * updated loose versions
  	 */
  	result = git_path_direach(&refs_path, _dirent_loose_load, backend);
  	git_buf_free(&refs_path);
  
  	return result;
  }
  
  static int refdb_fs_backend__exists(
  	int *exists,
  	git_refdb_backend *_backend,
  	const char *ref_name)
  {
  	refdb_fs_backend *backend;
  	git_buf ref_path = GIT_BUF_INIT;
  
  	assert(_backend);
  	backend = (refdb_fs_backend *)_backend;
  
  	if (packed_load(backend) < 0)
  		return -1;
  
  	if (git_buf_joinpath(&ref_path, backend->path, ref_name) < 0)
  		return -1;
  
  	if (git_path_isfile(ref_path.ptr) == true ||
  		git_strmap_exists(backend->refcache.packfile, ref_path.ptr))
  		*exists = 1;
  	else
  		*exists = 0;
  
  	git_buf_free(&ref_path);
  	return 0;
  }
  
  static const char *loose_parse_symbolic(git_buf *file_content)
  {
  	const unsigned int header_len = (unsigned int)strlen(GIT_SYMREF);
  	const char *refname_start;
  
  	refname_start = (const char *)file_content->ptr;
  
  	if (git_buf_len(file_content) < header_len + 1) {
  		giterr_set(GITERR_REFERENCE, "Corrupted loose reference file");
  		return NULL;
  	}
  
  	/*
  	 * Assume we have already checked for the header
  	 * before calling this function
  	 */
  	refname_start += header_len;
  
  	return refname_start;
  }
  
  static int loose_lookup(
  	git_reference **out,
  	refdb_fs_backend *backend,
  	const char *ref_name)
  {
  	const char *target;
  	git_oid oid;
  	git_buf ref_file = GIT_BUF_INIT;
  	int error = 0;
  
  	error = reference_read(&ref_file, NULL, backend->path, ref_name, NULL);
  
  	if (error < 0)
  		goto done;
  
  	if (git__prefixcmp((const char *)(ref_file.ptr), GIT_SYMREF) == 0) {
  		git_buf_rtrim(&ref_file);
  
  		if ((target = loose_parse_symbolic(&ref_file)) == NULL) {
  			error = -1;
  			goto done;
  		}
  
  		*out = git_reference__alloc(backend->refdb, ref_name, NULL, target);
  	} else {
  		if ((error = loose_parse_oid(&oid, &ref_file)) < 0)
  			goto done;
  		
  		*out = git_reference__alloc(backend->refdb, ref_name, &oid, NULL);
  	}
  
  	if (*out == NULL)
  		error = -1;
  
  done:
  	git_buf_free(&ref_file);
  	return error;
  }
  
  static int packed_map_entry(
  	struct packref **entry,
  	khiter_t *pos,
  	refdb_fs_backend *backend,
  	const char *ref_name)
  {
  	git_strmap *packfile_refs;
  
  	if (packed_load(backend) < 0)
  		return -1;
  	
  	/* Look up on the packfile */
  	packfile_refs = backend->refcache.packfile;
  
  	*pos = git_strmap_lookup_index(packfile_refs, ref_name);
  	
  	if (!git_strmap_valid_index(packfile_refs, *pos)) {
  		giterr_set(GITERR_REFERENCE, "Reference '%s' not found", ref_name);
  		return GIT_ENOTFOUND;
  	}
  
  	*entry = git_strmap_value_at(packfile_refs, *pos);
  	
  	return 0;
  }
  
  static int packed_lookup(
  	git_reference **out,
  	refdb_fs_backend *backend,
  	const char *ref_name)
  {
  	struct packref *entry;
  	khiter_t pos;
  	int error = 0;
  	
  	if ((error = packed_map_entry(&entry, &pos, backend, ref_name)) < 0)
  		return error;
  
  	if ((*out = git_reference__alloc(backend->refdb, ref_name, &entry->oid, NULL)) == NULL)
  		return -1;
  	
  	return 0;
  }
  
  static int refdb_fs_backend__lookup(
  	git_reference **out,
  	git_refdb_backend *_backend,
  	const char *ref_name)
  {
  	refdb_fs_backend *backend;
  	int result;
  
  	assert(_backend);
  
  	backend = (refdb_fs_backend *)_backend;
  
  	if ((result = loose_lookup(out, backend, ref_name)) == 0)
  		return 0;
  
  	/* only try to lookup this reference on the packfile if it
  	 * wasn't found on the loose refs; not if there was a critical error */
  	if (result == GIT_ENOTFOUND) {
  		giterr_clear();
  		result = packed_lookup(out, backend, ref_name);
  	}
  
  	return result;
  }
  
  struct dirent_list_data {
  	refdb_fs_backend *backend;
  	size_t repo_path_len;
  	unsigned int list_type:2;
  
  	git_reference_foreach_cb callback;
  	void *callback_payload;
  	int callback_error;
  };
  
  static git_ref_t loose_guess_rtype(const git_buf *full_path)
  {
  	git_buf ref_file = GIT_BUF_INIT;
  	git_ref_t type;
  
  	type = GIT_REF_INVALID;
  
  	if (git_futils_readbuffer(&ref_file, full_path->ptr) == 0) {
  		if (git__prefixcmp((const char *)(ref_file.ptr), GIT_SYMREF) == 0)
  			type = GIT_REF_SYMBOLIC;
  		else
  			type = GIT_REF_OID;
  	}
  
  	git_buf_free(&ref_file);
  	return type;
  }
  
  static int _dirent_loose_listall(void *_data, git_buf *full_path)
  {
  	struct dirent_list_data *data = (struct dirent_list_data *)_data;
  	const char *file_path = full_path->ptr + data->repo_path_len;
  
  	if (git_path_isdir(full_path->ptr) == true)
  		return git_path_direach(full_path, _dirent_loose_listall, _data);
  
  	/* do not add twice a reference that exists already in the packfile */
  	if (git_strmap_exists(data->backend->refcache.packfile, file_path))
  		return 0;
  
  	if (data->list_type != GIT_REF_LISTALL) {
  		if ((data->list_type & loose_guess_rtype(full_path)) == 0)
  			return 0; /* we are filtering out this reference */
  	}
  
  	/* Locked references aren't returned */
  	if (!git__suffixcmp(file_path, GIT_FILELOCK_EXTENSION))
  		return 0;
  
  	if (data->callback(file_path, data->callback_payload))
  		data->callback_error = GIT_EUSER;
  
  	return data->callback_error;
  }
  
  static int refdb_fs_backend__foreach(
  	git_refdb_backend *_backend,
  	unsigned int list_type,
  	git_reference_foreach_cb callback,
  	void *payload)
  {
  	refdb_fs_backend *backend;
  	int result;
  	struct dirent_list_data data;
  	git_buf refs_path = GIT_BUF_INIT;
  	const char *ref_name;
  	void *ref = NULL;
  	
  	GIT_UNUSED(ref);
  
  	assert(_backend);
  	backend = (refdb_fs_backend *)_backend;
  
  	if (packed_load(backend) < 0)
  		return -1;
  	
  	/* list all the packed references first */
  	if (list_type & GIT_REF_OID) {
  		git_strmap_foreach(backend->refcache.packfile, ref_name, ref, {
  			if (callback(ref_name, payload))
  				return GIT_EUSER;
  		});
  	}
  
  	/* now list the loose references, trying not to
  	 * duplicate the ref names already in the packed-refs file */
  
  	data.repo_path_len = strlen(backend->path);
  	data.list_type = list_type;
  	data.backend = backend;
  	data.callback = callback;
  	data.callback_payload = payload;
  	data.callback_error = 0;
  
  	if (git_buf_joinpath(&refs_path, backend->path, GIT_REFS_DIR) < 0)
  		return -1;
  
  	result = git_path_direach(&refs_path, _dirent_loose_listall, &data);
  
  	git_buf_free(&refs_path);
  
  	return data.callback_error ? GIT_EUSER : result;
  }
  
  static int loose_write(refdb_fs_backend *backend, const git_reference *ref)
  {
  	git_filebuf file = GIT_FILEBUF_INIT;
  	git_buf ref_path = GIT_BUF_INIT;
  
  	/* Remove a possibly existing empty directory hierarchy
  	 * which name would collide with the reference name
  	 */
  	if (git_futils_rmdir_r(ref->name, backend->path,
  		GIT_RMDIR_SKIP_NONEMPTY) < 0)
  		return -1;
  
  	if (git_buf_joinpath(&ref_path, backend->path, ref->name) < 0)
  		return -1;
  
  	if (git_filebuf_open(&file, ref_path.ptr, GIT_FILEBUF_FORCE) < 0) {
  		git_buf_free(&ref_path);
  		return -1;
  	}
  
  	git_buf_free(&ref_path);
  
  	if (ref->type == GIT_REF_OID) {
  		char oid[GIT_OID_HEXSZ + 1];
  
  		git_oid_fmt(oid, &ref->target.oid);
  		oid[GIT_OID_HEXSZ] = '\0';
  
  		git_filebuf_printf(&file, "%s\n", oid);
  
  	} else if (ref->type == GIT_REF_SYMBOLIC) {
  		git_filebuf_printf(&file, GIT_SYMREF "%s\n", ref->target.symbolic);
  	} else {
  		assert(0); /* don't let this happen */
  	}
  
  	return git_filebuf_commit(&file, GIT_REFS_FILE_MODE);
  }
  
  static int packed_sort(const void *a, const void *b)
  {
  	const struct packref *ref_a = (const struct packref *)a;
  	const struct packref *ref_b = (const struct packref *)b;
  
  	return strcmp(ref_a->name, ref_b->name);
  }
  
  /*
   * Find out what object this reference resolves to.
   *
   * For references that point to a 'big' tag (e.g. an
   * actual tag object on the repository), we need to
   * cache on the packfile the OID of the object to
   * which that 'big tag' is pointing to.
   */
  static int packed_find_peel(refdb_fs_backend *backend, struct packref *ref)
  {
  	git_object *object;
  
  	if (ref->flags & GIT_PACKREF_HAS_PEEL)
  		return 0;
  
  	/*
  	 * Only applies to tags, i.e. references
  	 * in the /refs/tags folder
  	 */
  	if (git__prefixcmp(ref->name, GIT_REFS_TAGS_DIR) != 0)
  		return 0;
  
  	/*
  	 * Find the tagged object in the repository
  	 */
  	if (git_object_lookup(&object, backend->repo, &ref->oid, GIT_OBJ_ANY) < 0)
  		return -1;
  
  	/*
  	 * If the tagged object is a Tag object, we need to resolve it;
  	 * if the ref is actually a 'weak' ref, we don't need to resolve
  	 * anything.
  	 */
  	if (git_object_type(object) == GIT_OBJ_TAG) {
  		git_tag *tag = (git_tag *)object;
  
  		/*
  		 * Find the object pointed at by this tag
  		 */
  		git_oid_cpy(&ref->peel, git_tag_target_id(tag));
  		ref->flags |= GIT_PACKREF_HAS_PEEL;
  
  		/*
  		 * The reference has now cached the resolved OID, and is
  		 * marked at such. When written to the packfile, it'll be
  		 * accompanied by this resolved oid
  		 */
  	}
  
  	git_object_free(object);
  	return 0;
  }
  
  /*
   * Write a single reference into a packfile
   */
  static int packed_write_ref(struct packref *ref, git_filebuf *file)
  {
  	char oid[GIT_OID_HEXSZ + 1];
  
  	git_oid_fmt(oid, &ref->oid);
  	oid[GIT_OID_HEXSZ] = 0;
  
  	/*
  	 * For references that peel to an object in the repo, we must
  	 * write the resulting peel on a separate line, e.g.
  	 *
  	 *	6fa8a902cc1d18527e1355773c86721945475d37 refs/tags/libgit2-0.4
  	 *	^2ec0cb7959b0bf965d54f95453f5b4b34e8d3100
  	 *
  	 * This obviously only applies to tags.
  	 * The required peels have already been loaded into `ref->peel_target`.
  	 */
  	if (ref->flags & GIT_PACKREF_HAS_PEEL) {
  		char peel[GIT_OID_HEXSZ + 1];
  		git_oid_fmt(peel, &ref->peel);
  		peel[GIT_OID_HEXSZ] = 0;
  
  		if (git_filebuf_printf(file, "%s %s\n^%s\n", oid, ref->name, peel) < 0)
  			return -1;
  	} else {
  		if (git_filebuf_printf(file, "%s %s\n", oid, ref->name) < 0)
  			return -1;
  	}
  
  	return 0;
  }
  
  /*
   * Remove all loose references
   *
   * Once we have successfully written a packfile,
   * all the loose references that were packed must be
   * removed from disk.
   *
   * This is a dangerous method; make sure the packfile
   * is well-written, because we are destructing references
   * here otherwise.
   */
  static int packed_remove_loose(
  	refdb_fs_backend *backend,
  	git_vector *packing_list)
  {
  	unsigned int i;
  	git_buf full_path = GIT_BUF_INIT;
  	int failed = 0;
  
  	for (i = 0; i < packing_list->length; ++i) {
  		struct packref *ref = git_vector_get(packing_list, i);
  
  		if ((ref->flags & GIT_PACKREF_WAS_LOOSE) == 0)
  			continue;
  
  		if (git_buf_joinpath(&full_path, backend->path, ref->name) < 0)
  			return -1; /* critical; do not try to recover on oom */
  
  		if (git_path_exists(full_path.ptr) == true && p_unlink(full_path.ptr) < 0) {
  			if (failed)
  				continue;
  
  			giterr_set(GITERR_REFERENCE,
  				"Failed to remove loose reference '%s' after packing: %s",
  				full_path.ptr, strerror(errno));
  
  			failed = 1;
  		}
  
  		/*
  		 * if we fail to remove a single file, this is *not* good,
  		 * but we should keep going and remove as many as possible.
  		 * After we've removed as many files as possible, we return
  		 * the error code anyway.
  		 */
  	}
  
  	git_buf_free(&full_path);
  	return failed ? -1 : 0;
  }
  
  /*
   * Write all the contents in the in-memory packfile to disk.
   */
  static int packed_write(refdb_fs_backend *backend)
  {
  	git_filebuf pack_file = GIT_FILEBUF_INIT;
  	unsigned int i;
  	git_buf pack_file_path = GIT_BUF_INIT;
  	git_vector packing_list;
  	unsigned int total_refs;
  
  	assert(backend && backend->refcache.packfile);
  
  	total_refs =
  		(unsigned int)git_strmap_num_entries(backend->refcache.packfile);
  
  	if (git_vector_init(&packing_list, total_refs, packed_sort) < 0)
  		return -1;
  
  	/* Load all the packfile into a vector */
  	{
  		struct packref *reference;
  
  		/* cannot fail: vector already has the right size */
  		git_strmap_foreach_value(backend->refcache.packfile, reference, {
  			git_vector_insert(&packing_list, reference);
  		});
  	}
  
  	/* sort the vector so the entries appear sorted on the packfile */
  	git_vector_sort(&packing_list);
  
  	/* Now we can open the file! */
  	if (git_buf_joinpath(&pack_file_path,
  		backend->path, GIT_PACKEDREFS_FILE) < 0)
  		goto cleanup_memory;
  
  	if (git_filebuf_open(&pack_file, pack_file_path.ptr, 0) < 0)
  		goto cleanup_packfile;
  
  	/* Packfiles have a header... apparently
  	 * This is in fact not required, but we might as well print it
  	 * just for kicks */
  	if (git_filebuf_printf(&pack_file, "%s\n", GIT_PACKEDREFS_HEADER) < 0)
  		goto cleanup_packfile;
  
  	for (i = 0; i < packing_list.length; ++i) {
  		struct packref *ref = (struct packref *)git_vector_get(&packing_list, i);
  
  		if (packed_find_peel(backend, ref) < 0)
  			goto cleanup_packfile;
  
  		if (packed_write_ref(ref, &pack_file) < 0)
  			goto cleanup_packfile;
  	}
  
  	/* if we've written all the references properly, we can commit
  	 * the packfile to make the changes effective */
  	if (git_filebuf_commit(&pack_file, GIT_PACKEDREFS_FILE_MODE) < 0)
  		goto cleanup_memory;
  
  	/* when and only when the packfile has been properly written,
  	 * we can go ahead and remove the loose refs */
  	 if (packed_remove_loose(backend, &packing_list) < 0)
  		 goto cleanup_memory;
  
  	 {
  		struct stat st;
  		if (p_stat(pack_file_path.ptr, &st) == 0)
  			backend->refcache.packfile_time = st.st_mtime;
  	 }
  
  	git_vector_free(&packing_list);
  	git_buf_free(&pack_file_path);
  
  	/* we're good now */
  	return 0;
  
  cleanup_packfile:
  	git_filebuf_cleanup(&pack_file);
  
  cleanup_memory:
  	git_vector_free(&packing_list);
  	git_buf_free(&pack_file_path);
  
  	return -1;
  }
  
  static int refdb_fs_backend__write(
  	git_refdb_backend *_backend,
  	const git_reference *ref)
  {
  	refdb_fs_backend *backend;
  
  	assert(_backend);
  	backend = (refdb_fs_backend *)_backend;
  
  	return loose_write(backend, ref);
  }
  
  static int refdb_fs_backend__delete(
  	git_refdb_backend *_backend,
  	const git_reference *ref)
  {
  	refdb_fs_backend *backend;
  	git_repository *repo;
  	git_buf loose_path = GIT_BUF_INIT;
  	struct packref *pack_ref;
  	khiter_t pack_ref_pos;
  	int error = 0, pack_error;
  	bool loose_deleted;
  
  	assert(_backend);
  	assert(ref);
  
  	backend = (refdb_fs_backend *)_backend;
  	repo = backend->repo;
  
  	/* If a loose reference exists, remove it from the filesystem */
  	
  	if (git_buf_joinpath(&loose_path, repo->path_repository, ref->name) < 0)
  		return -1;
  
  	if (git_path_isfile(loose_path.ptr)) {
  		error = p_unlink(loose_path.ptr);
  		loose_deleted = 1;
  	}
  	
  	git_buf_free(&loose_path);
  
  	if (error != 0)
  		return error;
  
  	/* If a packed reference exists, remove it from the packfile and repack */
  
  	if ((pack_error = packed_map_entry(&pack_ref, &pack_ref_pos, backend, ref->name)) == 0) {
  		git_strmap_delete_at(backend->refcache.packfile, pack_ref_pos);
  		git__free(pack_ref);
  
  		error = packed_write(backend);
  	}
  	
  	if (pack_error == GIT_ENOTFOUND)
  		error = loose_deleted ? 0 : GIT_ENOTFOUND;
  	else
  		error = pack_error;
  
  	return error;
  }
  
  static int refdb_fs_backend__compress(git_refdb_backend *_backend)
  {
  	refdb_fs_backend *backend;
  
  	assert(_backend);
  	backend = (refdb_fs_backend *)_backend;
  
  	if (packed_load(backend) < 0 || /* load the existing packfile */
  		packed_loadloose(backend) < 0 || /* add all the loose refs */
  		packed_write(backend) < 0) /* write back to disk */
  		return -1;
  
  	return 0;
  }
  
  static void refcache_free(git_refcache *refs)
  {
  	assert(refs);
  
  	if (refs->packfile) {
  		struct packref *reference;
  
  		git_strmap_foreach_value(refs->packfile, reference, {
  			git__free(reference);
  		});
  
  		git_strmap_free(refs->packfile);
  	}
  }
  
  static void refdb_fs_backend__free(git_refdb_backend *_backend)
  {
  	refdb_fs_backend *backend;
  
  	assert(_backend);
  	backend = (refdb_fs_backend *)_backend;
  
  	refcache_free(&backend->refcache);
  	git__free(backend);
  }
  
  int git_refdb_backend_fs(
  	git_refdb_backend **backend_out,
  	git_repository *repository,
  	git_refdb *refdb)
  {
  	refdb_fs_backend *backend;
  
  	backend = git__calloc(1, sizeof(refdb_fs_backend));
  	GITERR_CHECK_ALLOC(backend);
  
  	backend->repo = repository;
  	backend->path = repository->path_repository;
  	backend->refdb = refdb;
  
  	backend->parent.exists = &refdb_fs_backend__exists;
  	backend->parent.lookup = &refdb_fs_backend__lookup;
  	backend->parent.foreach = &refdb_fs_backend__foreach;
  	backend->parent.write = &refdb_fs_backend__write;
  	backend->parent.delete = &refdb_fs_backend__delete;
  	backend->parent.compress = &refdb_fs_backend__compress;
  	backend->parent.free = &refdb_fs_backend__free;
  
  	*backend_out = (git_refdb_backend *)backend;
  	return 0;
  }
  

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