/* * 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 "common.h" #include #include "git2/object.h" #include "git2/sys/odb_backend.h" #include "fileops.h" #include "hash.h" #include "odb.h" #include "delta.h" #include "filebuf.h" #include "object.h" #include "git2/odb_backend.h" #include "git2/types.h" typedef struct { /* object header data */ git_otype type; /* object type */ size_t size; /* object size */ } obj_hdr; typedef struct { git_odb_stream stream; git_filebuf fbuf; } loose_writestream; typedef struct loose_backend { git_odb_backend parent; int object_zlib_level; /** loose object zlib compression level. */ int fsync_object_files; /** loose object file fsync flag. */ mode_t object_file_mode; mode_t object_dir_mode; size_t objects_dirlen; char objects_dir[GIT_FLEX_ARRAY]; } loose_backend; /* State structure for exploring directories, * in order to locate objects matching a short oid. */ typedef struct { size_t dir_len; unsigned char short_oid[GIT_OID_HEXSZ]; /* hex formatted oid to match */ size_t short_oid_len; int found; /* number of matching * objects already found */ unsigned char res_oid[GIT_OID_HEXSZ]; /* hex formatted oid of * the object found */ } loose_locate_object_state; /*********************************************************** * * MISCELLANEOUS HELPER FUNCTIONS * ***********************************************************/ static int object_file_name( git_buf *name, const loose_backend *be, const git_oid *id) { size_t alloclen; /* expand length for object root + 40 hex sha1 chars + 2 * '/' + '\0' */ GITERR_CHECK_ALLOC_ADD(&alloclen, be->objects_dirlen, GIT_OID_HEXSZ); GITERR_CHECK_ALLOC_ADD(&alloclen, alloclen, 3); if (git_buf_grow(name, alloclen) < 0) return -1; git_buf_set(name, be->objects_dir, be->objects_dirlen); git_path_to_dir(name); /* loose object filename: aa/aaa... (41 bytes) */ git_oid_pathfmt(name->ptr + name->size, id); name->size += GIT_OID_HEXSZ + 1; name->ptr[name->size] = '\0'; return 0; } static int object_mkdir(const git_buf *name, const loose_backend *be) { return git_futils_mkdir_relative( name->ptr + be->objects_dirlen, be->objects_dir, be->object_dir_mode, GIT_MKDIR_PATH | GIT_MKDIR_SKIP_LAST | GIT_MKDIR_VERIFY_DIR, NULL); } static size_t get_binary_object_header(obj_hdr *hdr, git_buf *obj) { unsigned long c; unsigned char *data = (unsigned char *)obj->ptr; size_t shift, size, used = 0; if (git_buf_len(obj) == 0) return 0; c = data[used++]; hdr->type = (c >> 4) & 7; size = c & 15; shift = 4; while (c & 0x80) { if (git_buf_len(obj) <= used) return 0; if (sizeof(size_t) * 8 <= shift) return 0; c = data[used++]; size += (c & 0x7f) << shift; shift += 7; } hdr->size = size; return used; } static size_t get_object_header(obj_hdr *hdr, unsigned char *data) { char c, typename[10]; size_t size, used = 0; /* * type name string followed by space. */ while ((c = data[used]) != ' ') { typename[used++] = c; if (used >= sizeof(typename)) return 0; } typename[used] = 0; if (used == 0) return 0; hdr->type = git_object_string2type(typename); used++; /* consume the space */ /* * length follows immediately in decimal (without * leading zeros). */ size = data[used++] - '0'; if (size > 9) return 0; if (size) { while ((c = data[used]) != '\0') { size_t d = c - '0'; if (d > 9) break; used++; size = size * 10 + d; } } hdr->size = size; /* * the length must be followed by a zero byte */ if (data[used++] != '\0') return 0; return used; } /*********************************************************** * * ZLIB RELATED FUNCTIONS * ***********************************************************/ static void init_stream(z_stream *s, void *out, size_t len) { memset(s, 0, sizeof(*s)); s->next_out = out; s->avail_out = (uInt)len; } static void set_stream_input(z_stream *s, void *in, size_t len) { s->next_in = in; s->avail_in = (uInt)len; } static void set_stream_output(z_stream *s, void *out, size_t len) { s->next_out = out; s->avail_out = (uInt)len; } static int start_inflate(z_stream *s, git_buf *obj, void *out, size_t len) { int status; init_stream(s, out, len); set_stream_input(s, obj->ptr, git_buf_len(obj)); if ((status = inflateInit(s)) < Z_OK) return status; return inflate(s, 0); } static void abort_inflate(z_stream *s) { inflateEnd(s); } static int finish_inflate(z_stream *s) { int status = Z_OK; while (status == Z_OK) status = inflate(s, Z_FINISH); inflateEnd(s); if ((status != Z_STREAM_END) || (s->avail_in != 0)) { giterr_set(GITERR_ZLIB, "failed to finish zlib inflation; stream aborted prematurely"); return -1; } return 0; } static int is_zlib_compressed_data(unsigned char *data) { unsigned int w; w = ((unsigned int)(data[0]) << 8) + data[1]; return (data[0] & 0x8F) == 0x08 && !(w % 31); } static int inflate_buffer(void *in, size_t inlen, void *out, size_t outlen) { z_stream zs; int status = Z_OK; memset(&zs, 0x0, sizeof(zs)); zs.next_out = out; zs.avail_out = (uInt)outlen; zs.next_in = in; zs.avail_in = (uInt)inlen; if (inflateInit(&zs) < Z_OK) { giterr_set(GITERR_ZLIB, "failed to inflate buffer"); return -1; } while (status == Z_OK) status = inflate(&zs, Z_FINISH); inflateEnd(&zs); if (status != Z_STREAM_END /* || zs.avail_in != 0 */ || zs.total_out != outlen) { giterr_set(GITERR_ZLIB, "failed to inflate buffer; stream aborted prematurely"); return -1; } return 0; } static void *inflate_tail(z_stream *s, void *hb, size_t used, obj_hdr *hdr) { unsigned char *buf, *head = hb; size_t tail, alloc_size; /* * allocate a buffer to hold the inflated data and copy the * initial sequence of inflated data from the tail of the * head buffer, if any. */ if (GIT_ADD_SIZET_OVERFLOW(&alloc_size, hdr->size, 1) || (buf = git__malloc(alloc_size)) == NULL) { inflateEnd(s); return NULL; } tail = s->total_out - used; if (used > 0 && tail > 0) { if (tail > hdr->size) tail = hdr->size; memcpy(buf, head + used, tail); } used = tail; /* * inflate the remainder of the object data, if any */ if (hdr->size < used) inflateEnd(s); else { set_stream_output(s, buf + used, hdr->size - used); if (finish_inflate(s)) { git__free(buf); return NULL; } } return buf; } /* * At one point, there was a loose object format that was intended to * mimic the format used in pack-files. This was to allow easy copying * of loose object data into packs. This format is no longer used, but * we must still read it. */ static int inflate_packlike_loose_disk_obj(git_rawobj *out, git_buf *obj) { unsigned char *in, *buf; obj_hdr hdr; size_t len, used, alloclen; /* * read the object header, which is an (uncompressed) * binary encoding of the object type and size. */ if ((used = get_binary_object_header(&hdr, obj)) == 0 || !git_object_typeisloose(hdr.type)) { giterr_set(GITERR_ODB, "failed to inflate loose object"); return -1; } /* * allocate a buffer and inflate the data into it */ GITERR_CHECK_ALLOC_ADD(&alloclen, hdr.size, 1); buf = git__malloc(alloclen); GITERR_CHECK_ALLOC(buf); in = ((unsigned char *)obj->ptr) + used; len = obj->size - used; if (inflate_buffer(in, len, buf, hdr.size) < 0) { git__free(buf); return -1; } buf[hdr.size] = '\0'; out->data = buf; out->len = hdr.size; out->type = hdr.type; return 0; } static int inflate_disk_obj(git_rawobj *out, git_buf *obj) { unsigned char head[64], *buf; z_stream zs; obj_hdr hdr; size_t used; /* * check for a pack-like loose object */ if (!is_zlib_compressed_data((unsigned char *)obj->ptr)) return inflate_packlike_loose_disk_obj(out, obj); /* * inflate the initial part of the io buffer in order * to parse the object header (type and size). */ if (start_inflate(&zs, obj, head, sizeof(head)) < Z_OK || (used = get_object_header(&hdr, head)) == 0 || !git_object_typeisloose(hdr.type)) { abort_inflate(&zs); giterr_set(GITERR_ODB, "failed to inflate disk object"); return -1; } /* * allocate a buffer and inflate the object data into it * (including the initial sequence in the head buffer). */ if ((buf = inflate_tail(&zs, head, used, &hdr)) == NULL) return -1; buf[hdr.size] = '\0'; out->data = buf; out->len = hdr.size; out->type = hdr.type; return 0; } /*********************************************************** * * ODB OBJECT READING & WRITING * * Backend for the public API; read headers and full objects * from the ODB. Write raw data to the ODB. * ***********************************************************/ static int read_loose(git_rawobj *out, git_buf *loc) { int error; git_buf obj = GIT_BUF_INIT; assert(out && loc); if (git_buf_oom(loc)) return -1; out->data = NULL; out->len = 0; out->type = GIT_OBJ_BAD; if (!(error = git_futils_readbuffer(&obj, loc->ptr))) error = inflate_disk_obj(out, &obj); git_buf_free(&obj); return error; } static int read_header_loose(git_rawobj *out, git_buf *loc) { int error = 0, z_return = Z_ERRNO, read_bytes; git_file fd; z_stream zs; obj_hdr header_obj; unsigned char raw_buffer[16], inflated_buffer[64]; assert(out && loc); if (git_buf_oom(loc)) return -1; out->data = NULL; if ((fd = git_futils_open_ro(loc->ptr)) < 0) return fd; init_stream(&zs, inflated_buffer, sizeof(inflated_buffer)); z_return = inflateInit(&zs); while (z_return == Z_OK) { if ((read_bytes = p_read(fd, raw_buffer, sizeof(raw_buffer))) > 0) { set_stream_input(&zs, raw_buffer, read_bytes); z_return = inflate(&zs, 0); } else z_return = Z_STREAM_END; } if ((z_return != Z_STREAM_END && z_return != Z_BUF_ERROR) || get_object_header(&header_obj, inflated_buffer) == 0 || git_object_typeisloose(header_obj.type) == 0) { giterr_set(GITERR_ZLIB, "failed to read loose object header"); error = -1; } else { out->len = header_obj.size; out->type = header_obj.type; } finish_inflate(&zs); p_close(fd); return error; } static int locate_object( git_buf *object_location, loose_backend *backend, const git_oid *oid) { int error = object_file_name(object_location, backend, oid); if (!error && !git_path_exists(object_location->ptr)) return GIT_ENOTFOUND; return error; } /* Explore an entry of a directory and see if it matches a short oid */ static int fn_locate_object_short_oid(void *state, git_buf *pathbuf) { loose_locate_object_state *sstate = (loose_locate_object_state *)state; if (git_buf_len(pathbuf) - sstate->dir_len != GIT_OID_HEXSZ - 2) { /* Entry cannot be an object. Continue to next entry */ return 0; } if (git_path_isdir(pathbuf->ptr) == false) { /* We are already in the directory matching the 2 first hex characters, * compare the first ncmp characters of the oids */ if (!memcmp(sstate->short_oid + 2, (unsigned char *)pathbuf->ptr + sstate->dir_len, sstate->short_oid_len - 2)) { if (!sstate->found) { sstate->res_oid[0] = sstate->short_oid[0]; sstate->res_oid[1] = sstate->short_oid[1]; memcpy(sstate->res_oid+2, pathbuf->ptr+sstate->dir_len, GIT_OID_HEXSZ-2); } sstate->found++; } } if (sstate->found > 1) return GIT_EAMBIGUOUS; return 0; } /* Locate an object matching a given short oid */ static int locate_object_short_oid( git_buf *object_location, git_oid *res_oid, loose_backend *backend, const git_oid *short_oid, size_t len) { char *objects_dir = backend->objects_dir; size_t dir_len = strlen(objects_dir), alloc_len; loose_locate_object_state state; int error; /* prealloc memory for OBJ_DIR/xx/xx..38x..xx */ GITERR_CHECK_ALLOC_ADD(&alloc_len, dir_len, GIT_OID_HEXSZ); GITERR_CHECK_ALLOC_ADD(&alloc_len, alloc_len, 3); if (git_buf_grow(object_location, alloc_len) < 0) return -1; git_buf_set(object_location, objects_dir, dir_len); git_path_to_dir(object_location); /* save adjusted position at end of dir so it can be restored later */ dir_len = git_buf_len(object_location); /* Convert raw oid to hex formatted oid */ git_oid_fmt((char *)state.short_oid, short_oid); /* Explore OBJ_DIR/xx/ where xx is the beginning of hex formatted short oid */ if (git_buf_put(object_location, (char *)state.short_oid, 3) < 0) return -1; object_location->ptr[object_location->size - 1] = '/'; /* Check that directory exists */ if (git_path_isdir(object_location->ptr) == false) return git_odb__error_notfound("no matching loose object for prefix", short_oid, len); state.dir_len = git_buf_len(object_location); state.short_oid_len = len; state.found = 0; /* Explore directory to find a unique object matching short_oid */ error = git_path_direach( object_location, 0, fn_locate_object_short_oid, &state); if (error < 0 && error != GIT_EAMBIGUOUS) return error; if (!state.found) return git_odb__error_notfound("no matching loose object for prefix", short_oid, len); if (state.found > 1) return git_odb__error_ambiguous("multiple matches in loose objects"); /* Convert obtained hex formatted oid to raw */ error = git_oid_fromstr(res_oid, (char *)state.res_oid); if (error) return error; /* Update the location according to the oid obtained */ GITERR_CHECK_ALLOC_ADD(&alloc_len, dir_len, GIT_OID_HEXSZ); GITERR_CHECK_ALLOC_ADD(&alloc_len, alloc_len, 2); git_buf_truncate(object_location, dir_len); if (git_buf_grow(object_location, alloc_len) < 0) return -1; git_oid_pathfmt(object_location->ptr + dir_len, res_oid); object_location->size += GIT_OID_HEXSZ + 1; object_location->ptr[object_location->size] = '\0'; return 0; } /*********************************************************** * * LOOSE BACKEND PUBLIC API * * Implement the git_odb_backend API calls * ***********************************************************/ static int loose_backend__read_header(size_t *len_p, git_otype *type_p, git_odb_backend *backend, const git_oid *oid) { git_buf object_path = GIT_BUF_INIT; git_rawobj raw; int error; assert(backend && oid); raw.len = 0; raw.type = GIT_OBJ_BAD; if (locate_object(&object_path, (loose_backend *)backend, oid) < 0) { error = git_odb__error_notfound("no matching loose object", oid, GIT_OID_HEXSZ); } else if ((error = read_header_loose(&raw, &object_path)) == 0) { *len_p = raw.len; *type_p = raw.type; } git_buf_free(&object_path); return error; } static int loose_backend__read(void **buffer_p, size_t *len_p, git_otype *type_p, git_odb_backend *backend, const git_oid *oid) { git_buf object_path = GIT_BUF_INIT; git_rawobj raw; int error = 0; assert(backend && oid); if (locate_object(&object_path, (loose_backend *)backend, oid) < 0) { error = git_odb__error_notfound("no matching loose object", oid, GIT_OID_HEXSZ); } else if ((error = read_loose(&raw, &object_path)) == 0) { *buffer_p = raw.data; *len_p = raw.len; *type_p = raw.type; } git_buf_free(&object_path); return error; } static int loose_backend__read_prefix( git_oid *out_oid, void **buffer_p, size_t *len_p, git_otype *type_p, git_odb_backend *backend, const git_oid *short_oid, size_t len) { int error = 0; assert(len >= GIT_OID_MINPREFIXLEN && len <= GIT_OID_HEXSZ); if (len == GIT_OID_HEXSZ) { /* We can fall back to regular read method */ error = loose_backend__read(buffer_p, len_p, type_p, backend, short_oid); if (!error) git_oid_cpy(out_oid, short_oid); } else { git_buf object_path = GIT_BUF_INIT; git_rawobj raw; assert(backend && short_oid); if ((error = locate_object_short_oid(&object_path, out_oid, (loose_backend *)backend, short_oid, len)) == 0 && (error = read_loose(&raw, &object_path)) == 0) { *buffer_p = raw.data; *len_p = raw.len; *type_p = raw.type; } git_buf_free(&object_path); } return error; } static int loose_backend__exists(git_odb_backend *backend, const git_oid *oid) { git_buf object_path = GIT_BUF_INIT; int error; assert(backend && oid); error = locate_object(&object_path, (loose_backend *)backend, oid); git_buf_free(&object_path); return !error; } static int loose_backend__exists_prefix( git_oid *out, git_odb_backend *backend, const git_oid *short_id, size_t len) { git_buf object_path = GIT_BUF_INIT; int error; assert(backend && out && short_id && len >= GIT_OID_MINPREFIXLEN); error = locate_object_short_oid( &object_path, out, (loose_backend *)backend, short_id, len); git_buf_free(&object_path); return error; } struct foreach_state { size_t dir_len; git_odb_foreach_cb cb; void *data; }; GIT_INLINE(int) filename_to_oid(git_oid *oid, const char *ptr) { int v, i = 0; if (strlen(ptr) != GIT_OID_HEXSZ+1) return -1; if (ptr[2] != '/') { return -1; } v = (git__fromhex(ptr[i]) << 4) | git__fromhex(ptr[i+1]); if (v < 0) return -1; oid->id[0] = (unsigned char) v; ptr += 3; for (i = 0; i < 38; i += 2) { v = (git__fromhex(ptr[i]) << 4) | git__fromhex(ptr[i + 1]); if (v < 0) return -1; oid->id[1 + i/2] = (unsigned char) v; } return 0; } static int foreach_object_dir_cb(void *_state, git_buf *path) { git_oid oid; struct foreach_state *state = (struct foreach_state *) _state; if (filename_to_oid(&oid, path->ptr + state->dir_len) < 0) return 0; return giterr_set_after_callback_function( state->cb(&oid, state->data), "git_odb_foreach"); } static int foreach_cb(void *_state, git_buf *path) { struct foreach_state *state = (struct foreach_state *) _state; /* non-dir is some stray file, ignore it */ if (!git_path_isdir(git_buf_cstr(path))) return 0; return git_path_direach(path, 0, foreach_object_dir_cb, state); } static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb cb, void *data) { char *objects_dir; int error; git_buf buf = GIT_BUF_INIT; struct foreach_state state; loose_backend *backend = (loose_backend *) _backend; assert(backend && cb); objects_dir = backend->objects_dir; git_buf_sets(&buf, objects_dir); git_path_to_dir(&buf); if (git_buf_oom(&buf)) return -1; memset(&state, 0, sizeof(state)); state.cb = cb; state.data = data; state.dir_len = git_buf_len(&buf); error = git_path_direach(&buf, 0, foreach_cb, &state); git_buf_free(&buf); return error; } static int loose_backend__stream_fwrite(git_odb_stream *_stream, const git_oid *oid) { loose_writestream *stream = (loose_writestream *)_stream; loose_backend *backend = (loose_backend *)_stream->backend; git_buf final_path = GIT_BUF_INIT; int error = 0; if (object_file_name(&final_path, backend, oid) < 0 || object_mkdir(&final_path, backend) < 0) error = -1; else error = git_filebuf_commit_at( &stream->fbuf, final_path.ptr); git_buf_free(&final_path); return error; } static int loose_backend__stream_write(git_odb_stream *_stream, const char *data, size_t len) { loose_writestream *stream = (loose_writestream *)_stream; return git_filebuf_write(&stream->fbuf, data, len); } static void loose_backend__stream_free(git_odb_stream *_stream) { loose_writestream *stream = (loose_writestream *)_stream; git_filebuf_cleanup(&stream->fbuf); git__free(stream); } static int filebuf_flags(loose_backend *backend) { int flags = GIT_FILEBUF_TEMPORARY | (backend->object_zlib_level << GIT_FILEBUF_DEFLATE_SHIFT); if (backend->fsync_object_files || git_repository__fsync_gitdir) flags |= GIT_FILEBUF_FSYNC; return flags; } static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_backend, git_off_t length, git_otype type) { loose_backend *backend; loose_writestream *stream = NULL; char hdr[64]; git_buf tmp_path = GIT_BUF_INIT; int hdrlen; assert(_backend && length >= 0); backend = (loose_backend *)_backend; *stream_out = NULL; hdrlen = git_odb__format_object_header(hdr, sizeof(hdr), length, type); stream = git__calloc(1, sizeof(loose_writestream)); GITERR_CHECK_ALLOC(stream); stream->stream.backend = _backend; stream->stream.read = NULL; /* read only */ stream->stream.write = &loose_backend__stream_write; stream->stream.finalize_write = &loose_backend__stream_fwrite; stream->stream.free = &loose_backend__stream_free; stream->stream.mode = GIT_STREAM_WRONLY; if (git_buf_joinpath(&tmp_path, backend->objects_dir, "tmp_object") < 0 || git_filebuf_open(&stream->fbuf, tmp_path.ptr, filebuf_flags(backend), backend->object_file_mode) < 0 || stream->stream.write((git_odb_stream *)stream, hdr, hdrlen) < 0) { git_filebuf_cleanup(&stream->fbuf); git__free(stream); stream = NULL; } git_buf_free(&tmp_path); *stream_out = (git_odb_stream *)stream; return !stream ? -1 : 0; } static int loose_backend__write(git_odb_backend *_backend, const git_oid *oid, const void *data, size_t len, git_otype type) { int error = 0, header_len; git_buf final_path = GIT_BUF_INIT; char header[64]; git_filebuf fbuf = GIT_FILEBUF_INIT; loose_backend *backend; backend = (loose_backend *)_backend; /* prepare the header for the file */ header_len = git_odb__format_object_header(header, sizeof(header), len, type); if (git_buf_joinpath(&final_path, backend->objects_dir, "tmp_object") < 0 || git_filebuf_open(&fbuf, final_path.ptr, filebuf_flags(backend), backend->object_file_mode) < 0) { error = -1; goto cleanup; } git_filebuf_write(&fbuf, header, header_len); git_filebuf_write(&fbuf, data, len); if (object_file_name(&final_path, backend, oid) < 0 || object_mkdir(&final_path, backend) < 0 || git_filebuf_commit_at(&fbuf, final_path.ptr) < 0) error = -1; cleanup: if (error < 0) git_filebuf_cleanup(&fbuf); git_buf_free(&final_path); return error; } static int loose_backend__freshen( git_odb_backend *_backend, const git_oid *oid) { loose_backend *backend = (loose_backend *)_backend; git_buf path = GIT_BUF_INIT; int error; if (object_file_name(&path, backend, oid) < 0) return -1; error = git_futils_touch(path.ptr, NULL); git_buf_free(&path); return error; } static void loose_backend__free(git_odb_backend *_backend) { loose_backend *backend; assert(_backend); backend = (loose_backend *)_backend; git__free(backend); } int git_odb_backend_loose( git_odb_backend **backend_out, const char *objects_dir, int compression_level, int do_fsync, unsigned int dir_mode, unsigned int file_mode) { loose_backend *backend; size_t objects_dirlen, alloclen; assert(backend_out && objects_dir); objects_dirlen = strlen(objects_dir); GITERR_CHECK_ALLOC_ADD(&alloclen, sizeof(loose_backend), objects_dirlen); GITERR_CHECK_ALLOC_ADD(&alloclen, alloclen, 2); backend = git__calloc(1, alloclen); GITERR_CHECK_ALLOC(backend); backend->parent.version = GIT_ODB_BACKEND_VERSION; backend->objects_dirlen = objects_dirlen; memcpy(backend->objects_dir, objects_dir, objects_dirlen); if (backend->objects_dir[backend->objects_dirlen - 1] != '/') backend->objects_dir[backend->objects_dirlen++] = '/'; if (compression_level < 0) compression_level = Z_BEST_SPEED; if (dir_mode == 0) dir_mode = GIT_OBJECT_DIR_MODE; if (file_mode == 0) file_mode = GIT_OBJECT_FILE_MODE; backend->object_zlib_level = compression_level; backend->fsync_object_files = do_fsync; backend->object_dir_mode = dir_mode; backend->object_file_mode = file_mode; backend->parent.read = &loose_backend__read; backend->parent.write = &loose_backend__write; backend->parent.read_prefix = &loose_backend__read_prefix; backend->parent.read_header = &loose_backend__read_header; backend->parent.writestream = &loose_backend__stream; backend->parent.exists = &loose_backend__exists; backend->parent.exists_prefix = &loose_backend__exists_prefix; backend->parent.foreach = &loose_backend__foreach; backend->parent.freshen = &loose_backend__freshen; backend->parent.free = &loose_backend__free; *backend_out = (git_odb_backend *)backend; return 0; }