git/object-file.c

/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 *
 * This handles basic git object files - packing, unpacking,
 * creation etc.
 */
#include "cache.h"
#include "config.h"
#include "string-list.h"
#include "lockfile.h"
#include "delta.h"
#include "pack.h"
#include "blob.h"
#include "commit.h"
#include "run-command.h"
#include "tag.h"
#include "tree.h"
#include "tree-walk.h"
#include "refs.h"
#include "pack-revindex.h"
#include "hash-lookup.h"
#include "bulk-checkin.h"
#include "repository.h"
#include "replace-object.h"
#include "streaming.h"
#include "dir.h"
#include "list.h"
#include "mergesort.h"
#include "quote.h"
#include "packfile.h"
#include "object-store.h"
#include "promisor-remote.h"
#include "submodule.h"
#include "fsck.h"
#include "hook.h"
#include "sigchain.h"
#include "sub-process.h"
#include "pkt-line.h"
#include "gvfs-helper-client.h"

/* The maximum size for an object header. */
#define MAX_HEADER_LEN 32


#define EMPTY_TREE_SHA1_BIN_LITERAL \
	 "\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
	 "\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
#define EMPTY_TREE_SHA256_BIN_LITERAL \
	"\x6e\xf1\x9b\x41\x22\x5c\x53\x69\xf1\xc1" \
	"\x04\xd4\x5d\x8d\x85\xef\xa9\xb0\x57\xb5" \
	"\x3b\x14\xb4\xb9\xb9\x39\xdd\x74\xde\xcc" \
	"\x53\x21"

#define EMPTY_BLOB_SHA1_BIN_LITERAL \
	"\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b" \
	"\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91"
#define EMPTY_BLOB_SHA256_BIN_LITERAL \
	"\x47\x3a\x0f\x4c\x3b\xe8\xa9\x36\x81\xa2" \
	"\x67\xe3\xb1\xe9\xa7\xdc\xda\x11\x85\x43" \
	"\x6f\xe1\x41\xf7\x74\x91\x20\xa3\x03\x72" \
	"\x18\x13"

static const struct object_id empty_tree_oid = {
	.hash = EMPTY_TREE_SHA1_BIN_LITERAL,
	.algo = GIT_HASH_SHA1,
};
static const struct object_id empty_blob_oid = {
	.hash = EMPTY_BLOB_SHA1_BIN_LITERAL,
	.algo = GIT_HASH_SHA1,
};
static const struct object_id null_oid_sha1 = {
	.hash = {0},
	.algo = GIT_HASH_SHA1,
};
static const struct object_id empty_tree_oid_sha256 = {
	.hash = EMPTY_TREE_SHA256_BIN_LITERAL,
	.algo = GIT_HASH_SHA256,
};
static const struct object_id empty_blob_oid_sha256 = {
	.hash = EMPTY_BLOB_SHA256_BIN_LITERAL,
	.algo = GIT_HASH_SHA256,
};
static const struct object_id null_oid_sha256 = {
	.hash = {0},
	.algo = GIT_HASH_SHA256,
};

static void git_hash_sha1_init(git_hash_ctx *ctx)
{
	git_SHA1_Init(&ctx->sha1);
}

static void git_hash_sha1_clone(git_hash_ctx *dst, const git_hash_ctx *src)
{
	git_SHA1_Clone(&dst->sha1, &src->sha1);
}

static void git_hash_sha1_update(git_hash_ctx *ctx, const void *data, size_t len)
{
	git_SHA1_Update(&ctx->sha1, data, len);
}

static void git_hash_sha1_final(unsigned char *hash, git_hash_ctx *ctx)
{
	git_SHA1_Final(hash, &ctx->sha1);
}

static void git_hash_sha1_final_oid(struct object_id *oid, git_hash_ctx *ctx)
{
	git_SHA1_Final(oid->hash, &ctx->sha1);
	memset(oid->hash + GIT_SHA1_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA1_RAWSZ);
	oid->algo = GIT_HASH_SHA1;
}


static void git_hash_sha256_init(git_hash_ctx *ctx)
{
	git_SHA256_Init(&ctx->sha256);
}

static void git_hash_sha256_clone(git_hash_ctx *dst, const git_hash_ctx *src)
{
	git_SHA256_Clone(&dst->sha256, &src->sha256);
}

static void git_hash_sha256_update(git_hash_ctx *ctx, const void *data, size_t len)
{
	git_SHA256_Update(&ctx->sha256, data, len);
}

static void git_hash_sha256_final(unsigned char *hash, git_hash_ctx *ctx)
{
	git_SHA256_Final(hash, &ctx->sha256);
}

static void git_hash_sha256_final_oid(struct object_id *oid, git_hash_ctx *ctx)
{
	git_SHA256_Final(oid->hash, &ctx->sha256);
	/*
	 * This currently does nothing, so the compiler should optimize it out,
	 * but keep it in case we extend the hash size again.
	 */
	memset(oid->hash + GIT_SHA256_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA256_RAWSZ);
	oid->algo = GIT_HASH_SHA256;
}

static void git_hash_unknown_init(git_hash_ctx *ctx UNUSED)
{
	BUG("trying to init unknown hash");
}

static void git_hash_unknown_clone(git_hash_ctx *dst UNUSED,
				   const git_hash_ctx *src UNUSED)
{
	BUG("trying to clone unknown hash");
}

static void git_hash_unknown_update(git_hash_ctx *ctx UNUSED,
				    const void *data UNUSED,
				    size_t len UNUSED)
{
	BUG("trying to update unknown hash");
}

static void git_hash_unknown_final(unsigned char *hash UNUSED,
				   git_hash_ctx *ctx UNUSED)
{
	BUG("trying to finalize unknown hash");
}

static void git_hash_unknown_final_oid(struct object_id *oid UNUSED,
				       git_hash_ctx *ctx UNUSED)
{
	BUG("trying to finalize unknown hash");
}

const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
	{
		.name = NULL,
		.format_id = 0x00000000,
		.rawsz = 0,
		.hexsz = 0,
		.blksz = 0,
		.init_fn = git_hash_unknown_init,
		.clone_fn = git_hash_unknown_clone,
		.update_fn = git_hash_unknown_update,
		.final_fn = git_hash_unknown_final,
		.final_oid_fn = git_hash_unknown_final_oid,
		.empty_tree = NULL,
		.empty_blob = NULL,
		.null_oid = NULL,
	},
	{
		.name = "sha1",
		.format_id = GIT_SHA1_FORMAT_ID,
		.rawsz = GIT_SHA1_RAWSZ,
		.hexsz = GIT_SHA1_HEXSZ,
		.blksz = GIT_SHA1_BLKSZ,
		.init_fn = git_hash_sha1_init,
		.clone_fn = git_hash_sha1_clone,
		.update_fn = git_hash_sha1_update,
		.final_fn = git_hash_sha1_final,
		.final_oid_fn = git_hash_sha1_final_oid,
		.empty_tree = &empty_tree_oid,
		.empty_blob = &empty_blob_oid,
		.null_oid = &null_oid_sha1,
	},
	{
		.name = "sha256",
		.format_id = GIT_SHA256_FORMAT_ID,
		.rawsz = GIT_SHA256_RAWSZ,
		.hexsz = GIT_SHA256_HEXSZ,
		.blksz = GIT_SHA256_BLKSZ,
		.init_fn = git_hash_sha256_init,
		.clone_fn = git_hash_sha256_clone,
		.update_fn = git_hash_sha256_update,
		.final_fn = git_hash_sha256_final,
		.final_oid_fn = git_hash_sha256_final_oid,
		.empty_tree = &empty_tree_oid_sha256,
		.empty_blob = &empty_blob_oid_sha256,
		.null_oid = &null_oid_sha256,
	}
};

const struct object_id *null_oid(void)
{
	return the_hash_algo->null_oid;
}

const char *empty_tree_oid_hex(void)
{
	static char buf[GIT_MAX_HEXSZ + 1];
	return oid_to_hex_r(buf, the_hash_algo->empty_tree);
}

const char *empty_blob_oid_hex(void)
{
	static char buf[GIT_MAX_HEXSZ + 1];
	return oid_to_hex_r(buf, the_hash_algo->empty_blob);
}

int hash_algo_by_name(const char *name)
{
	int i;
	if (!name)
		return GIT_HASH_UNKNOWN;
	for (i = 1; i < GIT_HASH_NALGOS; i++)
		if (!strcmp(name, hash_algos[i].name))
			return i;
	return GIT_HASH_UNKNOWN;
}

int hash_algo_by_id(uint32_t format_id)
{
	int i;
	for (i = 1; i < GIT_HASH_NALGOS; i++)
		if (format_id == hash_algos[i].format_id)
			return i;
	return GIT_HASH_UNKNOWN;
}

int hash_algo_by_length(int len)
{
	int i;
	for (i = 1; i < GIT_HASH_NALGOS; i++)
		if (len == hash_algos[i].rawsz)
			return i;
	return GIT_HASH_UNKNOWN;
}

/*
 * This is meant to hold a *small* number of objects that you would
 * want read_object_file() to be able to return, but yet you do not want
 * to write them into the object store (e.g. a browse-only
 * application).
 */
static struct cached_object {
	struct object_id oid;
	enum object_type type;
	void *buf;
	unsigned long size;
} *cached_objects;
static int cached_object_nr, cached_object_alloc;

static struct cached_object empty_tree = {
	.oid = {
		.hash = EMPTY_TREE_SHA1_BIN_LITERAL,
	},
	.type = OBJ_TREE,
	.buf = "",
};

static struct cached_object *find_cached_object(const struct object_id *oid)
{
	int i;
	struct cached_object *co = cached_objects;

	for (i = 0; i < cached_object_nr; i++, co++) {
		if (oideq(&co->oid, oid))
			return co;
	}
	if (oideq(oid, the_hash_algo->empty_tree))
		return &empty_tree;
	return NULL;
}


static int get_conv_flags(unsigned flags)
{
	if (flags & HASH_RENORMALIZE)
		return CONV_EOL_RENORMALIZE;
	else if (flags & HASH_WRITE_OBJECT)
		return global_conv_flags_eol | CONV_WRITE_OBJECT;
	else
		return 0;
}


int mkdir_in_gitdir(const char *path)
{
	if (mkdir(path, 0777)) {
		int saved_errno = errno;
		struct stat st;
		struct strbuf sb = STRBUF_INIT;

		if (errno != EEXIST)
			return -1;
		/*
		 * Are we looking at a path in a symlinked worktree
		 * whose original repository does not yet have it?
		 * e.g. .git/rr-cache pointing at its original
		 * repository in which the user hasn't performed any
		 * conflict resolution yet?
		 */
		if (lstat(path, &st) || !S_ISLNK(st.st_mode) ||
		    strbuf_readlink(&sb, path, st.st_size) ||
		    !is_absolute_path(sb.buf) ||
		    mkdir(sb.buf, 0777)) {
			strbuf_release(&sb);
			errno = saved_errno;
			return -1;
		}
		strbuf_release(&sb);
	}
	return adjust_shared_perm(path);
}

static enum scld_error safe_create_leading_directories_1(char *path, int share)
{
	char *next_component = path + offset_1st_component(path);
	enum scld_error ret = SCLD_OK;

	while (ret == SCLD_OK && next_component) {
		struct stat st;
		char *slash = next_component, slash_character;

		while (*slash && !is_dir_sep(*slash))
			slash++;

		if (!*slash)
			break;

		next_component = slash + 1;
		while (is_dir_sep(*next_component))
			next_component++;
		if (!*next_component)
			break;

		slash_character = *slash;
		*slash = '\0';
		if (!stat(path, &st)) {
			/* path exists */
			if (!S_ISDIR(st.st_mode)) {
				errno = ENOTDIR;
				ret = SCLD_EXISTS;
			}
		} else if (mkdir(path, 0777)) {
			if (errno == EEXIST &&
			    !stat(path, &st) && S_ISDIR(st.st_mode))
				; /* somebody created it since we checked */
			else if (errno == ENOENT)
				/*
				 * Either mkdir() failed because
				 * somebody just pruned the containing
				 * directory, or stat() failed because
				 * the file that was in our way was
				 * just removed.  Either way, inform
				 * the caller that it might be worth
				 * trying again:
				 */
				ret = SCLD_VANISHED;
			else
				ret = SCLD_FAILED;
		} else if (share && adjust_shared_perm(path)) {
			ret = SCLD_PERMS;
		}
		*slash = slash_character;
	}
	return ret;
}

enum scld_error safe_create_leading_directories(char *path)
{
	return safe_create_leading_directories_1(path, 1);
}

enum scld_error safe_create_leading_directories_no_share(char *path)
{
	return safe_create_leading_directories_1(path, 0);
}

enum scld_error safe_create_leading_directories_const(const char *path)
{
	int save_errno;
	/* path points to cache entries, so xstrdup before messing with it */
	char *buf = xstrdup(path);
	enum scld_error result = safe_create_leading_directories(buf);

	save_errno = errno;
	free(buf);
	errno = save_errno;
	return result;
}

static void fill_loose_path(struct strbuf *buf, const struct object_id *oid)
{
	int i;
	for (i = 0; i < the_hash_algo->rawsz; i++) {
		static char hex[] = "0123456789abcdef";
		unsigned int val = oid->hash[i];
		strbuf_addch(buf, hex[val >> 4]);
		strbuf_addch(buf, hex[val & 0xf]);
		if (!i)
			strbuf_addch(buf, '/');
	}
}

static const char *odb_loose_path(struct object_directory *odb,
				  struct strbuf *buf,
				  const struct object_id *oid)
{
	strbuf_reset(buf);
	strbuf_addstr(buf, odb->path);
	strbuf_addch(buf, '/');
	fill_loose_path(buf, oid);
	return buf->buf;
}

const char *loose_object_path(struct repository *r, struct strbuf *buf,
			      const struct object_id *oid)
{
	return odb_loose_path(r->objects->odb, buf, oid);
}

static int gvfs_matched_shared_cache_to_alternate;

/*
 * Return non-zero iff the path is usable as an alternate object database.
 */
static int alt_odb_usable(struct raw_object_store *o,
			  struct strbuf *path,
			  const char *normalized_objdir, khiter_t *pos)
{
	int r;

	if (!strbuf_cmp(path, &gvfs_shared_cache_pathname)) {
		/*
		 * `gvfs.sharedCache` is the preferred alternate that we
		 * will use with `gvfs-helper.exe` to dynamically fetch
		 * missing objects.  It is set during git_default_config().
		 *
		 * Make sure the directory exists on disk before we let the
		 * stock code discredit it.
		 */
		struct strbuf buf_pack_foo = STRBUF_INIT;
		enum scld_error scld;

		/*
		 * Force create the "<odb>" and "<odb>/pack" directories, if
		 * not present on disk.  Append an extra bogus directory to
		 * get safe_create_leading_directories() to see "<odb>/pack"
		 * as a leading directory of something deeper (which it
		 * won't create).
		 */
		strbuf_addf(&buf_pack_foo, "%s/pack/foo", path->buf);

		scld = safe_create_leading_directories(buf_pack_foo.buf);
		if (scld != SCLD_OK && scld != SCLD_EXISTS) {
			error_errno(_("could not create shared-cache ODB '%s'"),
				    gvfs_shared_cache_pathname.buf);

			strbuf_release(&buf_pack_foo);

			/*
			 * Pretend no shared-cache was requested and
			 * effectively fallback to ".git/objects" for
			 * fetching missing objects.
			 */
			strbuf_release(&gvfs_shared_cache_pathname);
			return 0;
		}

		/*
		 * We know that there is an alternate (either from
		 * .git/objects/info/alternates or from a memory-only
		 * entry) associated with the shared-cache directory.
		 */
		gvfs_matched_shared_cache_to_alternate++;
		strbuf_release(&buf_pack_foo);
	}

	/* Detect cases where alternate disappeared */
	if (!is_directory(path->buf)) {
		error(_("object directory %s does not exist; "
			"check .git/objects/info/alternates"),
		      path->buf);
		return 0;
	}

	/*
	 * Prevent the common mistake of listing the same
	 * thing twice, or object directory itself.
	 */
	if (!o->odb_by_path) {
		khiter_t p;

		o->odb_by_path = kh_init_odb_path_map();
		assert(!o->odb->next);
		p = kh_put_odb_path_map(o->odb_by_path, o->odb->path, &r);
		assert(r == 1); /* never used */
		kh_value(o->odb_by_path, p) = o->odb;
	}
	if (fspatheq(path->buf, normalized_objdir))
		return 0;
	*pos = kh_put_odb_path_map(o->odb_by_path, path->buf, &r);
	/* r: 0 = exists, 1 = never used, 2 = deleted */
	return r == 0 ? 0 : 1;
}

/*
 * Prepare alternate object database registry.
 *
 * The variable alt_odb_list points at the list of struct
 * object_directory.  The elements on this list come from
 * non-empty elements from colon separated ALTERNATE_DB_ENVIRONMENT
 * environment variable, and $GIT_OBJECT_DIRECTORY/info/alternates,
 * whose contents is similar to that environment variable but can be
 * LF separated.  Its base points at a statically allocated buffer that
 * contains "/the/directory/corresponding/to/.git/objects/...", while
 * its name points just after the slash at the end of ".git/objects/"
 * in the example above, and has enough space to hold all hex characters
 * of the object ID, an extra slash for the first level indirection, and
 * the terminating NUL.
 */
static void read_info_alternates(struct repository *r,
				 const char *relative_base,
				 int depth);
static int link_alt_odb_entry(struct repository *r, const struct strbuf *entry,
	const char *relative_base, int depth, const char *normalized_objdir)
{
	struct object_directory *ent;
	struct strbuf pathbuf = STRBUF_INIT;
	struct strbuf tmp = STRBUF_INIT;
	khiter_t pos;
	int ret = -1;

	if (!is_absolute_path(entry->buf) && relative_base) {
		strbuf_realpath(&pathbuf, relative_base, 1);
		strbuf_addch(&pathbuf, '/');
	}
	strbuf_addbuf(&pathbuf, entry);

	if (!strbuf_realpath(&tmp, pathbuf.buf, 0)) {
		error(_("unable to normalize alternate object path: %s"),
		      pathbuf.buf);
		goto error;
	}
	strbuf_swap(&pathbuf, &tmp);

	/*
	 * The trailing slash after the directory name is given by
	 * this function at the end. Remove duplicates.
	 */
	while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
		strbuf_setlen(&pathbuf, pathbuf.len - 1);

	if (!alt_odb_usable(r->objects, &pathbuf, normalized_objdir, &pos))
		goto error;

	CALLOC_ARRAY(ent, 1);
	/* pathbuf.buf is already in r->objects->odb_by_path */
	ent->path = strbuf_detach(&pathbuf, NULL);

	/* add the alternate entry */
	*r->objects->odb_tail = ent;
	r->objects->odb_tail = &(ent->next);
	ent->next = NULL;
	assert(r->objects->odb_by_path);
	kh_value(r->objects->odb_by_path, pos) = ent;

	/* recursively add alternates */
	read_info_alternates(r, ent->path, depth + 1);
	ret = 0;
 error:
	strbuf_release(&tmp);
	strbuf_release(&pathbuf);
	return ret;
}

static const char *parse_alt_odb_entry(const char *string,
				       int sep,
				       struct strbuf *out)
{
	const char *end;

	strbuf_reset(out);

	if (*string == '#') {
		/* comment; consume up to next separator */
		end = strchrnul(string, sep);
	} else if (*string == '"' && !unquote_c_style(out, string, &end)) {
		/*
		 * quoted path; unquote_c_style has copied the
		 * data for us and set "end". Broken quoting (e.g.,
		 * an entry that doesn't end with a quote) falls
		 * back to the unquoted case below.
		 */
	} else {
		/* normal, unquoted path */
		end = strchrnul(string, sep);
		strbuf_add(out, string, end - string);
	}

	if (*end)
		end++;
	return end;
}

static void link_alt_odb_entries(struct repository *r, const char *alt,
				 int sep, const char *relative_base, int depth)
{
	struct strbuf objdirbuf = STRBUF_INIT;
	struct strbuf entry = STRBUF_INIT;

	if (!alt || !*alt)
		return;

	if (depth > 5) {
		error(_("%s: ignoring alternate object stores, nesting too deep"),
				relative_base);
		return;
	}

	strbuf_realpath(&objdirbuf, r->objects->odb->path, 1);

	while (*alt) {
		alt = parse_alt_odb_entry(alt, sep, &entry);
		if (!entry.len)
			continue;
		link_alt_odb_entry(r, &entry,
				   relative_base, depth, objdirbuf.buf);
	}
	strbuf_release(&entry);
	strbuf_release(&objdirbuf);
}

static void read_info_alternates(struct repository *r,
				 const char *relative_base,
				 int depth)
{
	char *path;
	struct strbuf buf = STRBUF_INIT;

	path = xstrfmt("%s/info/alternates", relative_base);
	if (strbuf_read_file(&buf, path, 1024) < 0) {
		warn_on_fopen_errors(path);
		free(path);
		return;
	}

	link_alt_odb_entries(r, buf.buf, '\n', relative_base, depth);
	strbuf_release(&buf);
	free(path);
}

void add_to_alternates_file(const char *reference)
{
	struct lock_file lock = LOCK_INIT;
	char *alts = git_pathdup("objects/info/alternates");
	FILE *in, *out;
	int found = 0;

	hold_lock_file_for_update(&lock, alts, LOCK_DIE_ON_ERROR);
	out = fdopen_lock_file(&lock, "w");
	if (!out)
		die_errno(_("unable to fdopen alternates lockfile"));

	in = fopen(alts, "r");
	if (in) {
		struct strbuf line = STRBUF_INIT;

		while (strbuf_getline(&line, in) != EOF) {
			if (!strcmp(reference, line.buf)) {
				found = 1;
				break;
			}
			fprintf_or_die(out, "%s\n", line.buf);
		}

		strbuf_release(&line);
		fclose(in);
	}
	else if (errno != ENOENT)
		die_errno(_("unable to read alternates file"));

	if (found) {
		rollback_lock_file(&lock);
	} else {
		fprintf_or_die(out, "%s\n", reference);
		if (commit_lock_file(&lock))
			die_errno(_("unable to move new alternates file into place"));
		if (the_repository->objects->loaded_alternates)
			link_alt_odb_entries(the_repository, reference,
					     '\n', NULL, 0);
	}
	free(alts);
}

void add_to_alternates_memory(const char *reference)
{
	/*
	 * Make sure alternates are initialized, or else our entry may be
	 * overwritten when they are.
	 */
	prepare_alt_odb(the_repository);

	link_alt_odb_entries(the_repository, reference,
			     '\n', NULL, 0);
}

struct object_directory *set_temporary_primary_odb(const char *dir, int will_destroy)
{
	struct object_directory *new_odb;

	/*
	 * Make sure alternates are initialized, or else our entry may be
	 * overwritten when they are.
	 */
	prepare_alt_odb(the_repository);

	/*
	 * Make a new primary odb and link the old primary ODB in as an
	 * alternate
	 */
	new_odb = xcalloc(1, sizeof(*new_odb));
	new_odb->path = xstrdup(dir);

	/*
	 * Disable ref updates while a temporary odb is active, since
	 * the objects in the database may roll back.
	 */
	new_odb->disable_ref_updates = 1;
	new_odb->will_destroy = will_destroy;
	new_odb->next = the_repository->objects->odb;
	the_repository->objects->odb = new_odb;
	return new_odb->next;
}

void restore_primary_odb(struct object_directory *restore_odb, const char *old_path)
{
	struct object_directory *cur_odb = the_repository->objects->odb;

	if (strcmp(old_path, cur_odb->path))
		BUG("expected %s as primary object store; found %s",
		    old_path, cur_odb->path);

	if (cur_odb->next != restore_odb)
		BUG("we expect the old primary object store to be the first alternate");

	the_repository->objects->odb = restore_odb;
	free_object_directory(cur_odb);
}

/*
 * Compute the exact path an alternate is at and returns it. In case of
 * error NULL is returned and the human readable error is added to `err`
 * `path` may be relative and should point to $GIT_DIR.
 * `err` must not be null.
 */
char *compute_alternate_path(const char *path, struct strbuf *err)
{
	char *ref_git = NULL;
	const char *repo;
	int seen_error = 0;

	ref_git = real_pathdup(path, 0);
	if (!ref_git) {
		seen_error = 1;
		strbuf_addf(err, _("path '%s' does not exist"), path);
		goto out;
	}

	repo = read_gitfile(ref_git);
	if (!repo)
		repo = read_gitfile(mkpath("%s/.git", ref_git));
	if (repo) {
		free(ref_git);
		ref_git = xstrdup(repo);
	}

	if (!repo && is_directory(mkpath("%s/.git/objects", ref_git))) {
		char *ref_git_git = mkpathdup("%s/.git", ref_git);
		free(ref_git);
		ref_git = ref_git_git;
	} else if (!is_directory(mkpath("%s/objects", ref_git))) {
		struct strbuf sb = STRBUF_INIT;
		seen_error = 1;
		if (get_common_dir(&sb, ref_git)) {
			strbuf_addf(err,
				    _("reference repository '%s' as a linked "
				      "checkout is not supported yet."),
				    path);
			goto out;
		}

		strbuf_addf(err, _("reference repository '%s' is not a "
					"local repository."), path);
		goto out;
	}

	if (!access(mkpath("%s/shallow", ref_git), F_OK)) {
		strbuf_addf(err, _("reference repository '%s' is shallow"),
			    path);
		seen_error = 1;
		goto out;
	}

	if (!access(mkpath("%s/info/grafts", ref_git), F_OK)) {
		strbuf_addf(err,
			    _("reference repository '%s' is grafted"),
			    path);
		seen_error = 1;
		goto out;
	}

out:
	if (seen_error) {
		FREE_AND_NULL(ref_git);
	}

	return ref_git;
}

struct object_directory *find_odb(struct repository *r, const char *obj_dir)
{
	struct object_directory *odb;
	char *obj_dir_real = real_pathdup(obj_dir, 1);
	struct strbuf odb_path_real = STRBUF_INIT;

	prepare_alt_odb(r);
	for (odb = r->objects->odb; odb; odb = odb->next) {
		strbuf_realpath(&odb_path_real, odb->path, 1);
		if (!strcmp(obj_dir_real, odb_path_real.buf))
			break;
	}

	free(obj_dir_real);
	strbuf_release(&odb_path_real);

	if (!odb)
		die(_("could not find object directory matching %s"), obj_dir);
	return odb;
}

static void fill_alternate_refs_command(struct child_process *cmd,
					const char *repo_path)
{
	const char *value;

	if (!git_config_get_value("core.alternateRefsCommand", &value)) {
		cmd->use_shell = 1;

		strvec_push(&cmd->args, value);
		strvec_push(&cmd->args, repo_path);
	} else {
		cmd->git_cmd = 1;

		strvec_pushf(&cmd->args, "--git-dir=%s", repo_path);
		strvec_push(&cmd->args, "for-each-ref");
		strvec_push(&cmd->args, "--format=%(objectname)");

		if (!git_config_get_value("core.alternateRefsPrefixes", &value)) {
			strvec_push(&cmd->args, "--");
			strvec_split(&cmd->args, value);
		}
	}

	strvec_pushv(&cmd->env, (const char **)local_repo_env);
	cmd->out = -1;
}

static void read_alternate_refs(const char *path,
				alternate_ref_fn *cb,
				void *data)
{
	struct child_process cmd = CHILD_PROCESS_INIT;
	struct strbuf line = STRBUF_INIT;
	FILE *fh;

	fill_alternate_refs_command(&cmd, path);

	if (start_command(&cmd))
		return;

	fh = xfdopen(cmd.out, "r");
	while (strbuf_getline_lf(&line, fh) != EOF) {
		struct object_id oid;
		const char *p;

		if (parse_oid_hex(line.buf, &oid, &p) || *p) {
			warning(_("invalid line while parsing alternate refs: %s"),
				line.buf);
			break;
		}

		cb(&oid, data);
	}

	fclose(fh);
	finish_command(&cmd);
	strbuf_release(&line);
}

struct alternate_refs_data {
	alternate_ref_fn *fn;
	void *data;
};

static int refs_from_alternate_cb(struct object_directory *e,
				  void *data)
{
	struct strbuf path = STRBUF_INIT;
	size_t base_len;
	struct alternate_refs_data *cb = data;

	if (!strbuf_realpath(&path, e->path, 0))
		goto out;
	if (!strbuf_strip_suffix(&path, "/objects"))
		goto out;
	base_len = path.len;

	/* Is this a git repository with refs? */
	strbuf_addstr(&path, "/refs");
	if (!is_directory(path.buf))
		goto out;
	strbuf_setlen(&path, base_len);

	read_alternate_refs(path.buf, cb->fn, cb->data);

out:
	strbuf_release(&path);
	return 0;
}

void for_each_alternate_ref(alternate_ref_fn fn, void *data)
{
	struct alternate_refs_data cb;
	cb.fn = fn;
	cb.data = data;
	foreach_alt_odb(refs_from_alternate_cb, &cb);
}

int foreach_alt_odb(alt_odb_fn fn, void *cb)
{
	struct object_directory *ent;
	int r = 0;

	prepare_alt_odb(the_repository);
	for (ent = the_repository->objects->odb->next; ent; ent = ent->next) {
		r = fn(ent, cb);
		if (r)
			break;
	}
	return r;
}

void prepare_alt_odb(struct repository *r)
{
	if (r->objects->loaded_alternates)
		return;

	link_alt_odb_entries(r, r->objects->alternate_db, PATH_SEP, NULL, 0);

	read_info_alternates(r, r->objects->odb->path, 0);

	if (gvfs_shared_cache_pathname.len &&
	    !gvfs_matched_shared_cache_to_alternate) {
		/*
		 * There is no entry in .git/objects/info/alternates for
		 * the requested shared-cache directory.  Therefore, the
		 * odb-list does not contain this directory.
		 *
		 * Force this directory into the odb-list as an in-memory
		 * alternate.  Implicitly create the directory on disk, if
		 * necessary.
		 *
		 * See GIT_ALTERNATE_OBJECT_DIRECTORIES for another example
		 * of this kind of usage.
		 *
		 * Note: This has the net-effect of allowing Git to treat
		 * `gvfs.sharedCache` as an unofficial alternate.  This
		 * usage should be discouraged for compatbility reasons
		 * with other tools in the overall Git ecosystem (that
		 * won't know about this trick).  It would be much better
		 * for us to update .git/objects/info/alternates instead.
		 * The code here is considered a backstop.
		 */
		link_alt_odb_entries(r, gvfs_shared_cache_pathname.buf,
				     '\n', NULL, 0);
	}

	r->objects->loaded_alternates = 1;
}

#define CAP_GET    (1u<<0)

static int subprocess_map_initialized;
static struct hashmap subprocess_map;

struct read_object_process {
	struct subprocess_entry subprocess;
	unsigned int supported_capabilities;
};

static int start_read_object_fn(struct subprocess_entry *subprocess)
{
	struct read_object_process *entry = (struct read_object_process *)subprocess;
	static int versions[] = {1, 0};
	static struct subprocess_capability capabilities[] = {
		{ "get", CAP_GET },
		{ NULL, 0 }
	};

	return subprocess_handshake(subprocess, "git-read-object", versions,
				    NULL, capabilities,
				    &entry->supported_capabilities);
}

static int read_object_process(const struct object_id *oid)
{
	int err;
	struct read_object_process *entry;
	struct child_process *process;
	struct strbuf status = STRBUF_INIT;
	const char *cmd = find_hook("read-object");
	uint64_t start;

	start = getnanotime();

	trace2_region_enter("subprocess", "read_object", the_repository);

	if (!subprocess_map_initialized) {
		subprocess_map_initialized = 1;
		hashmap_init(&subprocess_map, (hashmap_cmp_fn)cmd2process_cmp,
			     NULL, 0);
		entry = NULL;
	} else {
		entry = (struct read_object_process *) subprocess_find_entry(&subprocess_map, cmd);
	}

	if (!entry) {
		entry = xmalloc(sizeof(*entry));
		entry->supported_capabilities = 0;

		if (subprocess_start(&subprocess_map, &entry->subprocess, cmd,
				     start_read_object_fn)) {
			free(entry);
			err = -1;
			goto leave_region;
		}
	}
	process = &entry->subprocess.process;

	if (!(CAP_GET & entry->supported_capabilities)) {
		err = -1;
		goto leave_region;
	}

	sigchain_push(SIGPIPE, SIG_IGN);

	err = packet_write_fmt_gently(process->in, "command=get\n");
	if (err)
		goto done;

	err = packet_write_fmt_gently(process->in, "sha1=%s\n", oid_to_hex(oid));
	if (err)
		goto done;

	err = packet_flush_gently(process->in);
	if (err)
		goto done;

	err = subprocess_read_status(process->out, &status);
	err = err ? err : strcmp(status.buf, "success");

done:
	sigchain_pop(SIGPIPE);

	if (err || errno == EPIPE) {
		err = err ? err : errno;
		if (!strcmp(status.buf, "error")) {
			/* The process signaled a problem with the file. */
		}
		else if (!strcmp(status.buf, "abort")) {
			/*
			 * The process signaled a permanent problem. Don't try to read
			 * objects with the same command for the lifetime of the current
			 * Git process.
			 */
			entry->supported_capabilities &= ~CAP_GET;
		}
		else {
			/*
			 * Something went wrong with the read-object process.
			 * Force shutdown and restart if needed.
			 */
			error("external process '%s' failed", cmd);
			subprocess_stop(&subprocess_map,
					(struct subprocess_entry *)entry);
			free(entry);
		}
	}

	trace_performance_since(start, "read_object_process");

leave_region:
	trace2_region_leave_printf("subprocess", "read_object", the_repository,
				   "result %d", err);

	return err;
}

/* Returns 1 if we have successfully freshened the file, 0 otherwise. */
static int freshen_file(const char *fn)
{
	return !utime(fn, NULL);
}

/*
 * All of the check_and_freshen functions return 1 if the file exists and was
 * freshened (if freshening was requested), 0 otherwise. If they return
 * 0, you should not assume that it is safe to skip a write of the object (it
 * either does not exist on disk, or has a stale mtime and may be subject to
 * pruning).
 */
int check_and_freshen_file(const char *fn, int freshen)
{
	if (access(fn, F_OK))
		return 0;
	if (freshen && !freshen_file(fn))
		return 0;
	return 1;
}

static int check_and_freshen_odb(struct object_directory *odb,
				 const struct object_id *oid,
				 int freshen)
{
	static struct strbuf path = STRBUF_INIT;
	odb_loose_path(odb, &path, oid);
	return check_and_freshen_file(path.buf, freshen);
}

static int check_and_freshen_local(const struct object_id *oid, int freshen)
{
	return check_and_freshen_odb(the_repository->objects->odb, oid, freshen);
}

static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
{
	struct object_directory *odb;

	prepare_alt_odb(the_repository);
	for (odb = the_repository->objects->odb->next; odb; odb = odb->next) {
		if (check_and_freshen_odb(odb, oid, freshen))
			return 1;
	}
	return 0;
}

static int check_and_freshen(const struct object_id *oid, int freshen,
			     int skip_virtualized_objects)
{
	int ret;
	int tried_hook = 0;

retry:
	ret = check_and_freshen_local(oid, freshen) ||
	       check_and_freshen_nonlocal(oid, freshen);
	if (!ret && core_virtualize_objects && !skip_virtualized_objects &&
	    !tried_hook) {
		tried_hook = 1;
		if (!read_object_process(oid))
			goto retry;
	}

	return ret;
}

int has_loose_object_nonlocal(const struct object_id *oid)
{
	return check_and_freshen_nonlocal(oid, 0);
}

int has_loose_object(const struct object_id *oid)
{
	return check_and_freshen(oid, 0, 0);
}

static void mmap_limit_check(size_t length)
{
	static size_t limit = 0;
	if (!limit) {
		limit = git_env_ulong("GIT_MMAP_LIMIT", 0);
		if (!limit)
			limit = SIZE_MAX;
	}
	if (length > limit)
		die(_("attempting to mmap %"PRIuMAX" over limit %"PRIuMAX),
		    (uintmax_t)length, (uintmax_t)limit);
}

void *xmmap_gently(void *start, size_t length,
		  int prot, int flags, int fd, off_t offset)
{
	void *ret;

	mmap_limit_check(length);
	ret = mmap(start, length, prot, flags, fd, offset);
	if (ret == MAP_FAILED && !length)
		ret = NULL;
	return ret;
}

const char *mmap_os_err(void)
{
	static const char blank[] = "";
#if defined(__linux__)
	if (errno == ENOMEM) {
		/* this continues an existing error message: */
		static const char enomem[] =
", check sys.vm.max_map_count and/or RLIMIT_DATA";
		return enomem;
	}
#endif /* OS-specific bits */
	return blank;
}

void *xmmap(void *start, size_t length,
	int prot, int flags, int fd, off_t offset)
{
	void *ret = xmmap_gently(start, length, prot, flags, fd, offset);
	if (ret == MAP_FAILED)
		die_errno(_("mmap failed%s"), mmap_os_err());
	return ret;
}

static int format_object_header_literally(char *str, size_t size,
					  const char *type, size_t objsize)
{
	return xsnprintf(str, size, "%s %"PRIuMAX, type, (uintmax_t)objsize) + 1;
}

int format_object_header(char *str, size_t size, enum object_type type,
			 size_t objsize)
{
	const char *name = type_name(type);

	if (!name)
		BUG("could not get a type name for 'enum object_type' value %d", type);

	return format_object_header_literally(str, size, name, objsize);
}

int check_object_signature(struct repository *r, const struct object_id *oid,
			   void *buf, unsigned long size,
			   enum object_type type)
{
	struct object_id real_oid;

	hash_object_file(r->hash_algo, buf, size, type, &real_oid);

	return !oideq(oid, &real_oid) ? -1 : 0;
}

int stream_object_signature(struct repository *r, const struct object_id *oid)
{
	struct object_id real_oid;
	unsigned long size;
	enum object_type obj_type;
	struct git_istream *st;
	git_hash_ctx c;
	char hdr[MAX_HEADER_LEN];
	int hdrlen;

	st = open_istream(r, oid, &obj_type, &size, NULL);
	if (!st)
		return -1;

	/* Generate the header */
	hdrlen = format_object_header(hdr, sizeof(hdr), obj_type, size);

	/* Sha1.. */
	r->hash_algo->init_fn(&c);
	r->hash_algo->update_fn(&c, hdr, hdrlen);
	for (;;) {
		char buf[1024 * 16];
		ssize_t readlen = read_istream(st, buf, sizeof(buf));

		if (readlen < 0) {
			close_istream(st);
			return -1;
		}
		if (!readlen)
			break;
		r->hash_algo->update_fn(&c, buf, readlen);
	}
	r->hash_algo->final_oid_fn(&real_oid, &c);
	close_istream(st);
	return !oideq(oid, &real_oid) ? -1 : 0;
}

int git_open_cloexec(const char *name, int flags)
{
	int fd;
	static int o_cloexec = O_CLOEXEC;

	fd = open(name, flags | o_cloexec);
	if ((o_cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) {
		/* Try again w/o O_CLOEXEC: the kernel might not support it */
		o_cloexec &= ~O_CLOEXEC;
		fd = open(name, flags | o_cloexec);
	}

#if defined(F_GETFD) && defined(F_SETFD) && defined(FD_CLOEXEC)
	{
		static int fd_cloexec = FD_CLOEXEC;

		if (!o_cloexec && 0 <= fd && fd_cloexec) {
			/* Opened w/o O_CLOEXEC?  try with fcntl(2) to add it */
			int flags = fcntl(fd, F_GETFD);
			if (fcntl(fd, F_SETFD, flags | fd_cloexec))
				fd_cloexec = 0;
		}
	}
#endif
	return fd;
}

/*
 * Find "oid" as a loose object in the local repository or in an alternate.
 * Returns 0 on success, negative on failure.
 *
 * The "path" out-parameter will give the path of the object we found (if any).
 * Note that it may point to static storage and is only valid until another
 * call to stat_loose_object().
 */
static int stat_loose_object(struct repository *r, const struct object_id *oid,
			     struct stat *st, const char **path)
{
	struct object_directory *odb;
	static struct strbuf buf = STRBUF_INIT;

	prepare_alt_odb(r);
	for (odb = r->objects->odb; odb; odb = odb->next) {
		*path = odb_loose_path(odb, &buf, oid);
		if (!lstat(*path, st))
			return 0;
	}

	return -1;
}

/*
 * Like stat_loose_object(), but actually open the object and return the
 * descriptor. See the caveats on the "path" parameter above.
 */
static int open_loose_object(struct repository *r,
			     const struct object_id *oid, const char **path)
{
	int fd;
	struct object_directory *odb;
	int most_interesting_errno = ENOENT;
	static struct strbuf buf = STRBUF_INIT;

	prepare_alt_odb(r);
	for (odb = r->objects->odb; odb; odb = odb->next) {
		*path = odb_loose_path(odb, &buf, oid);
		fd = git_open(*path);
		if (fd >= 0)
			return fd;

		if (most_interesting_errno == ENOENT)
			most_interesting_errno = errno;
	}
	errno = most_interesting_errno;
	return -1;
}

static int quick_has_loose(struct repository *r,
			   const struct object_id *oid)
{
	struct object_directory *odb;

	prepare_alt_odb(r);
	for (odb = r->objects->odb; odb; odb = odb->next) {
		if (oidtree_contains(odb_loose_cache(odb, oid), oid))
			return 1;
	}
	return 0;
}

/*
 * Map and close the given loose object fd. The path argument is used for
 * error reporting.
 */
static void *map_fd(int fd, const char *path, unsigned long *size)
{
	void *map = NULL;
	struct stat st;

	if (!fstat(fd, &st)) {
		*size = xsize_t(st.st_size);
		if (!*size) {
			/* mmap() is forbidden on empty files */
			error(_("object file %s is empty"), path);
			close(fd);
			return NULL;
		}
		map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
	}
	close(fd);
	return map;
}

void *map_loose_object(struct repository *r,
		       const struct object_id *oid,
		       unsigned long *size)
{
	const char *p;
	int fd = open_loose_object(r, oid, &p);

	if (fd < 0)
		return NULL;
	return map_fd(fd, p, size);
}

enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
						    unsigned char *map,
						    unsigned long mapsize,
						    void *buffer,
						    unsigned long bufsiz,
						    struct strbuf *header)
{
	int status;

	/* Get the data stream */
	memset(stream, 0, sizeof(*stream));
	stream->next_in = map;
	stream->avail_in = mapsize;
	stream->next_out = buffer;
	stream->avail_out = bufsiz;

	git_inflate_init(stream);
	obj_read_unlock();
	status = git_inflate(stream, 0);
	obj_read_lock();
	if (status < Z_OK)
		return ULHR_BAD;

	/*
	 * Check if entire header is unpacked in the first iteration.
	 */
	if (memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
		return ULHR_OK;

	/*
	 * We have a header longer than MAX_HEADER_LEN. The "header"
	 * here is only non-NULL when we run "cat-file
	 * --allow-unknown-type".
	 */
	if (!header)
		return ULHR_TOO_LONG;

	/*
	 * buffer[0..bufsiz] was not large enough.  Copy the partial
	 * result out to header, and then append the result of further
	 * reading the stream.
	 */
	strbuf_add(header, buffer, stream->next_out - (unsigned char *)buffer);
	stream->next_out = buffer;
	stream->avail_out = bufsiz;

	do {
		obj_read_unlock();
		status = git_inflate(stream, 0);
		obj_read_lock();
		strbuf_add(header, buffer, stream->next_out - (unsigned char *)buffer);
		if (memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
			return 0;
		stream->next_out = buffer;
		stream->avail_out = bufsiz;
	} while (status != Z_STREAM_END);
	return ULHR_TOO_LONG;
}

static void *unpack_loose_rest(git_zstream *stream,
			       void *buffer, unsigned long size,
			       const struct object_id *oid)
{
	int bytes = strlen(buffer) + 1;
	unsigned char *buf = xmallocz(size);
	unsigned long n;
	int status = Z_OK;

	n = stream->total_out - bytes;
	if (n > size)
		n = size;
	memcpy(buf, (char *) buffer + bytes, n);
	bytes = n;
	if (bytes <= size) {
		/*
		 * The above condition must be (bytes <= size), not
		 * (bytes < size).  In other words, even though we
		 * expect no more output and set avail_out to zero,
		 * the input zlib stream may have bytes that express
		 * "this concludes the stream", and we *do* want to
		 * eat that input.
		 *
		 * Otherwise we would not be able to test that we
		 * consumed all the input to reach the expected size;
		 * we also want to check that zlib tells us that all
		 * went well with status == Z_STREAM_END at the end.
		 */
		stream->next_out = buf + bytes;
		stream->avail_out = size - bytes;
		while (status == Z_OK) {
			obj_read_unlock();
			status = git_inflate(stream, Z_FINISH);
			obj_read_lock();
		}
	}
	if (status == Z_STREAM_END && !stream->avail_in) {
		git_inflate_end(stream);
		return buf;
	}

	if (status < 0)
		error(_("corrupt loose object '%s'"), oid_to_hex(oid));
	else if (stream->avail_in)
		error(_("garbage at end of loose object '%s'"),
		      oid_to_hex(oid));
	free(buf);
	return NULL;
}

/*
 * We used to just use "sscanf()", but that's actually way
 * too permissive for what we want to check. So do an anal
 * object header parse by hand.
 */
int parse_loose_header(const char *hdr, struct object_info *oi)
{
	const char *type_buf = hdr;
	size_t size;
	int type, type_len = 0;

	/*
	 * The type can be of any size but is followed by
	 * a space.
	 */
	for (;;) {
		char c = *hdr++;
		if (!c)
			return -1;
		if (c == ' ')
			break;
		type_len++;
	}

	type = type_from_string_gently(type_buf, type_len, 1);
	if (oi->type_name)
		strbuf_add(oi->type_name, type_buf, type_len);
	if (oi->typep)
		*oi->typep = type;

	/*
	 * The length must follow immediately, and be in canonical
	 * decimal format (ie "010" is not valid).
	 */
	size = *hdr++ - '0';
	if (size > 9)
		return -1;
	if (size) {
		for (;;) {
			unsigned long c = *hdr - '0';
			if (c > 9)
				break;
			hdr++;
			size = st_add(st_mult(size, 10), c);
		}
	}

	if (oi->sizep)
		*oi->sizep = cast_size_t_to_ulong(size);

	/*
	 * The length must be followed by a zero byte
	 */
	if (*hdr)
		return -1;

	/*
	 * The format is valid, but the type may still be bogus. The
	 * Caller needs to check its oi->typep.
	 */
	return 0;
}

static int loose_object_info(struct repository *r,
			     const struct object_id *oid,
			     struct object_info *oi, int flags)
{
	int status = 0;
	int fd;
	unsigned long mapsize;
	const char *path;
	void *map;
	git_zstream stream;
	char hdr[MAX_HEADER_LEN];
	struct strbuf hdrbuf = STRBUF_INIT;
	unsigned long size_scratch;
	enum object_type type_scratch;
	int allow_unknown = flags & OBJECT_INFO_ALLOW_UNKNOWN_TYPE;

	if (oi->delta_base_oid)
		oidclr(oi->delta_base_oid);

	/*
	 * If we don't care about type or size, then we don't
	 * need to look inside the object at all. Note that we
	 * do not optimize out the stat call, even if the
	 * caller doesn't care about the disk-size, since our
	 * return value implicitly indicates whether the
	 * object even exists.
	 */
	if (!oi->typep && !oi->type_name && !oi->sizep && !oi->contentp) {
		struct stat st;
		if (!oi->disk_sizep && (flags & OBJECT_INFO_QUICK))
			return quick_has_loose(r, oid) ? 0 : -1;
		if (stat_loose_object(r, oid, &st, &path) < 0)
			return -1;
		if (oi->disk_sizep)
			*oi->disk_sizep = st.st_size;
		return 0;
	}

	fd = open_loose_object(r, oid, &path);
	if (fd < 0) {
		if (errno != ENOENT)
			error_errno(_("unable to open loose object %s"), oid_to_hex(oid));
		return -1;
	}
	map = map_fd(fd, path, &mapsize);
	if (!map)
		return -1;

	if (!oi->sizep)
		oi->sizep = &size_scratch;
	if (!oi->typep)
		oi->typep = &type_scratch;

	if (oi->disk_sizep)
		*oi->disk_sizep = mapsize;

	switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
				    allow_unknown ? &hdrbuf : NULL)) {
	case ULHR_OK:
		if (parse_loose_header(hdrbuf.len ? hdrbuf.buf : hdr, oi) < 0)
			status = error(_("unable to parse %s header"), oid_to_hex(oid));
		else if (!allow_unknown && *oi->typep < 0)
			die(_("invalid object type"));

		if (!oi->contentp)
			break;
		*oi->contentp = unpack_loose_rest(&stream, hdr, *oi->sizep, oid);
		if (*oi->contentp)
			goto cleanup;

		status = -1;
		break;
	case ULHR_BAD:
		status = error(_("unable to unpack %s header"),
			       oid_to_hex(oid));
		break;
	case ULHR_TOO_LONG:
		status = error(_("header for %s too long, exceeds %d bytes"),
			       oid_to_hex(oid), MAX_HEADER_LEN);
		break;
	}

	if (status && (flags & OBJECT_INFO_DIE_IF_CORRUPT))
		die(_("loose object %s (stored in %s) is corrupt"),
		    oid_to_hex(oid), path);

	git_inflate_end(&stream);
cleanup:
	munmap(map, mapsize);
	if (oi->sizep == &size_scratch)
		oi->sizep = NULL;
	strbuf_release(&hdrbuf);
	if (oi->typep == &type_scratch)
		oi->typep = NULL;
	oi->whence = OI_LOOSE;
	return status;
}

int obj_read_use_lock = 0;
pthread_mutex_t obj_read_mutex;

void enable_obj_read_lock(void)
{
	if (obj_read_use_lock)
		return;

	obj_read_use_lock = 1;
	init_recursive_mutex(&obj_read_mutex);
}

void disable_obj_read_lock(void)
{
	if (!obj_read_use_lock)
		return;

	obj_read_use_lock = 0;
	pthread_mutex_destroy(&obj_read_mutex);
}

int fetch_if_missing = 1;

static int do_oid_object_info_extended(struct repository *r,
				       const struct object_id *oid,
				       struct object_info *oi, unsigned flags)
{
	static struct object_info blank_oi = OBJECT_INFO_INIT;
	struct cached_object *co;
	struct pack_entry e;
	int rtype;
	const struct object_id *real = oid;
	int already_retried = 0;
	int tried_hook = 0;
	int tried_gvfs_helper = 0;

	if (flags & OBJECT_INFO_LOOKUP_REPLACE)
		real = lookup_replace_object(r, oid);

	if (is_null_oid(real))
		return -1;

	if (!oi)
		oi = &blank_oi;

retry:
	co = find_cached_object(real);
	if (co) {
		if (oi->typep)
			*(oi->typep) = co->type;
		if (oi->sizep)
			*(oi->sizep) = co->size;
		if (oi->disk_sizep)
			*(oi->disk_sizep) = 0;
		if (oi->delta_base_oid)
			oidclr(oi->delta_base_oid);
		if (oi->type_name)
			strbuf_addstr(oi->type_name, type_name(co->type));
		if (oi->contentp)
			*oi->contentp = xmemdupz(co->buf, co->size);
		oi->whence = OI_CACHED;
		return 0;
	}

	while (1) {
		if (find_pack_entry(r, real, &e))
			break;

		/* Most likely it's a loose object. */
		if (!loose_object_info(r, real, oi, flags))
			return 0;

		if (core_use_gvfs_helper && !tried_gvfs_helper) {
			enum gh_client__created ghc;

			if (flags & OBJECT_INFO_SKIP_FETCH_OBJECT)
				return -1;

			gh_client__get_immediate(real, &ghc);
			tried_gvfs_helper = 1;

			/*
			 * Retry the lookup IIF `gvfs-helper` created one
			 * or more new packfiles or loose objects.
			 */
			if (ghc != GHC__CREATED__NOTHING)
				continue;

			/*
			 * If `gvfs-helper` fails, we just want to return -1.
			 * But allow the other providers to have a shot at it.
			 * (At least until we have a chance to consolidate
			 * them.)
			 */
		}

		/* Not a loose object; someone else may have just packed it. */
		if (!(flags & OBJECT_INFO_QUICK)) {
			reprepare_packed_git(r);
			if (find_pack_entry(r, real, &e))
				break;
			if (core_virtualize_objects && !tried_hook) {
				// TODO Assert or at least trace2 if gvfs-helper
				// TODO was tried and failed and then read-object-hook
				// TODO is successful at getting this object.
				tried_hook = 1;
				// TODO BUG? Should 'oid' be 'real' ?
				if (!read_object_process(oid))
					goto retry;
			}
		}

		/*
		 * If r is the_repository, this might be an attempt at
		 * accessing a submodule object as if it were in the_repository
		 * (having called add_submodule_odb() on that submodule's ODB).
		 * If any such ODBs exist, register them and try again.
		 */
		if (r == the_repository &&
		    register_all_submodule_odb_as_alternates())
			/* We added some alternates; retry */
			continue;

		/* Check if it is a missing object */
		if (fetch_if_missing && repo_has_promisor_remote(r) &&
		    !already_retried &&
		    !(flags & OBJECT_INFO_SKIP_FETCH_OBJECT)) {
			promisor_remote_get_direct(r, real, 1);
			already_retried = 1;
			continue;
		}

		if (flags & OBJECT_INFO_DIE_IF_CORRUPT) {
			const struct packed_git *p;
			if ((flags & OBJECT_INFO_LOOKUP_REPLACE) && !oideq(real, oid))
				die(_("replacement %s not found for %s"),
				    oid_to_hex(real), oid_to_hex(oid));
			if ((p = has_packed_and_bad(r, real)))
				die(_("packed object %s (stored in %s) is corrupt"),
				    oid_to_hex(real), p->pack_name);
		}
		return -1;
	}

	if (oi == &blank_oi)
		/*
		 * We know that the caller doesn't actually need the
		 * information below, so return early.
		 */
		return 0;
	rtype = packed_object_info(r, e.p, e.offset, oi);
	if (rtype < 0) {
		mark_bad_packed_object(e.p, real);
		return do_oid_object_info_extended(r, real, oi, 0);
	} else if (oi->whence == OI_PACKED) {
		oi->u.packed.offset = e.offset;
		oi->u.packed.pack = e.p;
		oi->u.packed.is_delta = (rtype == OBJ_REF_DELTA ||
					 rtype == OBJ_OFS_DELTA);
	}

	return 0;
}

int oid_object_info_extended(struct repository *r, const struct object_id *oid,
			     struct object_info *oi, unsigned flags)
{
	int ret;
	obj_read_lock();
	ret = do_oid_object_info_extended(r, oid, oi, flags);
	obj_read_unlock();
	return ret;
}


/* returns enum object_type or negative */
int oid_object_info(struct repository *r,
		    const struct object_id *oid,
		    unsigned long *sizep)
{
	enum object_type type;
	struct object_info oi = OBJECT_INFO_INIT;

	oi.typep = &type;
	oi.sizep = sizep;
	if (oid_object_info_extended(r, oid, &oi,
				      OBJECT_INFO_LOOKUP_REPLACE) < 0)
		return -1;
	return type;
}

int pretend_object_file(void *buf, unsigned long len, enum object_type type,
			struct object_id *oid)
{
	struct cached_object *co;

	hash_object_file(the_hash_algo, buf, len, type, oid);
	if (has_object_file_with_flags(oid, OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT) ||
	    find_cached_object(oid))
		return 0;
	ALLOC_GROW(cached_objects, cached_object_nr + 1, cached_object_alloc);
	co = &cached_objects[cached_object_nr++];
	co->size = len;
	co->type = type;
	co->buf = xmalloc(len);
	memcpy(co->buf, buf, len);
	oidcpy(&co->oid, oid);
	return 0;
}

/*
 * This function dies on corrupt objects; the callers who want to
 * deal with them should arrange to call oid_object_info_extended() and give
 * error messages themselves.
 */
void *repo_read_object_file(struct repository *r,
			    const struct object_id *oid,
			    enum object_type *type,
			    unsigned long *size)
{
	struct object_info oi = OBJECT_INFO_INIT;
	unsigned flags = OBJECT_INFO_DIE_IF_CORRUPT | OBJECT_INFO_LOOKUP_REPLACE;
	void *data;

	oi.typep = type;
	oi.sizep = size;
	oi.contentp = &data;
	if (oid_object_info_extended(r, oid, &oi, flags))
		return NULL;

	return data;
}

void *read_object_with_reference(struct repository *r,
				 const struct object_id *oid,
				 enum object_type required_type,
				 unsigned long *size,
				 struct object_id *actual_oid_return)
{
	enum object_type type;
	void *buffer;
	unsigned long isize;
	struct object_id actual_oid;

	oidcpy(&actual_oid, oid);
	while (1) {
		int ref_length = -1;
		const char *ref_type = NULL;

		buffer = repo_read_object_file(r, &actual_oid, &type, &isize);
		if (!buffer)
			return NULL;
		if (type == required_type) {
			*size = isize;
			if (actual_oid_return)
				oidcpy(actual_oid_return, &actual_oid);
			return buffer;
		}
		/* Handle references */
		else if (type == OBJ_COMMIT)
			ref_type = "tree ";
		else if (type == OBJ_TAG)
			ref_type = "object ";
		else {
			free(buffer);
			return NULL;
		}
		ref_length = strlen(ref_type);

		if (ref_length + the_hash_algo->hexsz > isize ||
		    memcmp(buffer, ref_type, ref_length) ||
		    get_oid_hex((char *) buffer + ref_length, &actual_oid)) {
			free(buffer);
			return NULL;
		}
		free(buffer);
		/* Now we have the ID of the referred-to object in
		 * actual_oid.  Check again. */
	}
}

static void hash_object_body(const struct git_hash_algo *algo, git_hash_ctx *c,
			     const void *buf, size_t len,
			     struct object_id *oid,
			     char *hdr, size_t *hdrlen)
{
	algo->init_fn(c);
	algo->update_fn(c, hdr, *hdrlen);
	algo->update_fn(c, buf, len);
	algo->final_oid_fn(oid, c);
}

static void write_object_file_prepare(const struct git_hash_algo *algo,
				      const void *buf, size_t len,
				      enum object_type type, struct object_id *oid,
				      char *hdr, size_t *hdrlen)
{
	git_hash_ctx c;

	/* Generate the header */
	*hdrlen = format_object_header(hdr, *hdrlen, type, len);

	/* Hash (function pointers) computation */
	hash_object_body(algo, &c, buf, len, oid, hdr, hdrlen);
}

static void write_object_file_prepare_literally(const struct git_hash_algo *algo,
				      const void *buf, size_t len,
				      const char *type, struct object_id *oid,
				      char *hdr, size_t *hdrlen)
{
	git_hash_ctx c;

	*hdrlen = format_object_header_literally(hdr, *hdrlen, type, len);
	hash_object_body(algo, &c, buf, len, oid, hdr, hdrlen);
}

/*
 * Move the just written object into its final resting place.
 */
int finalize_object_file(const char *tmpfile, const char *filename)
{
	int ret = 0;

	if (object_creation_mode == OBJECT_CREATION_USES_RENAMES)
		goto try_rename;
	else if (link(tmpfile, filename))
		ret = errno;

	/*
	 * Coda hack - coda doesn't like cross-directory links,
	 * so we fall back to a rename, which will mean that it
	 * won't be able to check collisions, but that's not a
	 * big deal.
	 *
	 * The same holds for FAT formatted media.
	 *
	 * When this succeeds, we just return.  We have nothing
	 * left to unlink.
	 */
	if (ret && ret != EEXIST) {
	try_rename:
		if (!rename(tmpfile, filename))
			goto out;
		ret = errno;
	}
	unlink_or_warn(tmpfile);
	if (ret) {
		if (ret != EEXIST) {
			return error_errno(_("unable to write file %s"), filename);
		}
		/* FIXME!!! Collision check here ? */
	}

out:
	if (adjust_shared_perm(filename))
		return error(_("unable to set permission to '%s'"), filename);
	return 0;
}

static void hash_object_file_literally(const struct git_hash_algo *algo,
				       const void *buf, size_t len,
				       const char *type, struct object_id *oid)
{
	char hdr[MAX_HEADER_LEN];
	size_t hdrlen = sizeof(hdr);

	write_object_file_prepare_literally(algo, buf, len, type, oid, hdr, &hdrlen);
}

void hash_object_file(const struct git_hash_algo *algo, const void *buf,
		      size_t len, enum object_type type,
		      struct object_id *oid)
{
	hash_object_file_literally(algo, buf, len, type_name(type), oid);
}

/* Finalize a file on disk, and close it. */
static void close_loose_object(int fd, const char *filename)
{
	if (the_repository->objects->odb->will_destroy)
		goto out;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		fsync_loose_object_bulk_checkin(fd, filename);
	else if (fsync_object_files > 0)
		fsync_or_die(fd, filename);
	else
		fsync_component_or_die(FSYNC_COMPONENT_LOOSE_OBJECT, fd,
				       filename);

out:
	if (close(fd) != 0)
		die_errno(_("error when closing loose object file"));
}

/* Size of directory component, including the ending '/' */
static inline int directory_size(const char *filename)
{
	const char *s = strrchr(filename, '/');
	if (!s)
		return 0;
	return s - filename + 1;
}

/*
 * This creates a temporary file in the same directory as the final
 * 'filename'
 *
 * We want to avoid cross-directory filename renames, because those
 * can have problems on various filesystems (FAT, NFS, Coda).
 */
static int create_tmpfile(struct strbuf *tmp, const char *filename)
{
	int fd, dirlen = directory_size(filename);

	strbuf_reset(tmp);
	strbuf_add(tmp, filename, dirlen);
	strbuf_addstr(tmp, "tmp_obj_XXXXXX");
	fd = git_mkstemp_mode(tmp->buf, 0444);
	if (fd < 0 && dirlen && errno == ENOENT) {
		/*
		 * Make sure the directory exists; note that the contents
		 * of the buffer are undefined after mkstemp returns an
		 * error, so we have to rewrite the whole buffer from
		 * scratch.
		 */
		strbuf_reset(tmp);
		strbuf_add(tmp, filename, dirlen - 1);
		if (mkdir(tmp->buf, 0777) && errno != EEXIST)
			return -1;
		if (adjust_shared_perm(tmp->buf))
			return -1;

		/* Try again */
		strbuf_addstr(tmp, "/tmp_obj_XXXXXX");
		fd = git_mkstemp_mode(tmp->buf, 0444);
	}
	return fd;
}

/**
 * Common steps for loose object writers to start writing loose
 * objects:
 *
 * - Create tmpfile for the loose object.
 * - Setup zlib stream for compression.
 * - Start to feed header to zlib stream.
 *
 * Returns a "fd", which should later be provided to
 * end_loose_object_common().
 */
static int start_loose_object_common(struct strbuf *tmp_file,
				     const char *filename, unsigned flags,
				     git_zstream *stream,
				     unsigned char *buf, size_t buflen,
				     git_hash_ctx *c,
				     char *hdr, int hdrlen)
{
	int fd;

	fd = create_tmpfile(tmp_file, filename);
	if (fd < 0) {
		if (flags & HASH_SILENT)
			return -1;
		else if (errno == EACCES)
			return error(_("insufficient permission for adding "
				       "an object to repository database %s"),
				     get_object_directory());
		else
			return error_errno(
				_("unable to create temporary file"));
	}

	/*  Setup zlib stream for compression */
	git_deflate_init(stream, zlib_compression_level);
	stream->next_out = buf;
	stream->avail_out = buflen;
	the_hash_algo->init_fn(c);

	/*  Start to feed header to zlib stream */
	stream->next_in = (unsigned char *)hdr;
	stream->avail_in = hdrlen;
	while (git_deflate(stream, 0) == Z_OK)
		; /* nothing */
	the_hash_algo->update_fn(c, hdr, hdrlen);

	return fd;
}

/**
 * Common steps for the inner git_deflate() loop for writing loose
 * objects. Returns what git_deflate() returns.
 */
static int write_loose_object_common(git_hash_ctx *c,
				     git_zstream *stream, const int flush,
				     unsigned char *in0, const int fd,
				     unsigned char *compressed,
				     const size_t compressed_len)
{
	int ret;

	ret = git_deflate(stream, flush ? Z_FINISH : 0);
	the_hash_algo->update_fn(c, in0, stream->next_in - in0);
	if (write_in_full(fd, compressed, stream->next_out - compressed) < 0)
		die_errno(_("unable to write loose object file"));
	stream->next_out = compressed;
	stream->avail_out = compressed_len;

	return ret;
}

/**
 * Common steps for loose object writers to end writing loose objects:
 *
 * - End the compression of zlib stream.
 * - Get the calculated oid to "oid".
 */
static int end_loose_object_common(git_hash_ctx *c, git_zstream *stream,
				   struct object_id *oid)
{
	int ret;

	ret = git_deflate_end_gently(stream);
	if (ret != Z_OK)
		return ret;
	the_hash_algo->final_oid_fn(oid, c);

	return Z_OK;
}

static int write_loose_object(const struct object_id *oid, char *hdr,
			      int hdrlen, const void *buf, unsigned long len,
			      time_t mtime, unsigned flags)
{
	int fd, ret;
	unsigned char compressed[4096];
	git_zstream stream;
	git_hash_ctx c;
	struct object_id parano_oid;
	static struct strbuf tmp_file = STRBUF_INIT;
	static struct strbuf filename = STRBUF_INIT;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		prepare_loose_object_bulk_checkin();

	loose_object_path(the_repository, &filename, oid);

	fd = start_loose_object_common(&tmp_file, filename.buf, flags,
				       &stream, compressed, sizeof(compressed),
				       &c, hdr, hdrlen);
	if (fd < 0)
		return -1;

	/* Then the data itself.. */
	stream.next_in = (void *)buf;
	stream.avail_in = len;
	do {
		unsigned char *in0 = stream.next_in;

		ret = write_loose_object_common(&c, &stream, 1, in0, fd,
						compressed, sizeof(compressed));
	} while (ret == Z_OK);

	if (ret != Z_STREAM_END)
		die(_("unable to deflate new object %s (%d)"), oid_to_hex(oid),
		    ret);
	ret = end_loose_object_common(&c, &stream, &parano_oid);
	if (ret != Z_OK)
		die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid),
		    ret);
	if (!oideq(oid, &parano_oid))
		die(_("confused by unstable object source data for %s"),
		    oid_to_hex(oid));

	close_loose_object(fd, tmp_file.buf);

	if (mtime) {
		struct utimbuf utb;
		utb.actime = mtime;
		utb.modtime = mtime;
		if (utime(tmp_file.buf, &utb) < 0 &&
		    !(flags & HASH_SILENT))
			warning_errno(_("failed utime() on %s"), tmp_file.buf);
	}

	return finalize_object_file(tmp_file.buf, filename.buf);
}

static int freshen_loose_object(const struct object_id *oid,
				int skip_virtualized_objects)
{
	return check_and_freshen(oid, 1, skip_virtualized_objects);
}

static int freshen_packed_object(const struct object_id *oid)
{
	struct pack_entry e;
	if (!find_pack_entry(the_repository, oid, &e))
		return 0;
	if (e.p->is_cruft)
		return 0;
	if (e.p->freshened)
		return 1;
	if (!freshen_file(e.p->pack_name))
		return 0;
	e.p->freshened = 1;
	return 1;
}

int stream_loose_object(struct input_stream *in_stream, size_t len,
			struct object_id *oid)
{
	int fd, ret, err = 0, flush = 0;
	unsigned char compressed[4096];
	git_zstream stream;
	git_hash_ctx c;
	struct strbuf tmp_file = STRBUF_INIT;
	struct strbuf filename = STRBUF_INIT;
	int dirlen;
	char hdr[MAX_HEADER_LEN];
	int hdrlen;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		prepare_loose_object_bulk_checkin();

	/* Since oid is not determined, save tmp file to odb path. */
	strbuf_addf(&filename, "%s/", get_object_directory());
	hdrlen = format_object_header(hdr, sizeof(hdr), OBJ_BLOB, len);

	/*
	 * Common steps for write_loose_object and stream_loose_object to
	 * start writing loose objects:
	 *
	 *  - Create tmpfile for the loose object.
	 *  - Setup zlib stream for compression.
	 *  - Start to feed header to zlib stream.
	 */
	fd = start_loose_object_common(&tmp_file, filename.buf, 0,
				       &stream, compressed, sizeof(compressed),
				       &c, hdr, hdrlen);
	if (fd < 0) {
		err = -1;
		goto cleanup;
	}

	/* Then the data itself.. */
	do {
		unsigned char *in0 = stream.next_in;

		if (!stream.avail_in && !in_stream->is_finished) {
			const void *in = in_stream->read(in_stream, &stream.avail_in);
			stream.next_in = (void *)in;
			in0 = (unsigned char *)in;
			/* All data has been read. */
			if (in_stream->is_finished)
				flush = 1;
		}
		ret = write_loose_object_common(&c, &stream, flush, in0, fd,
						compressed, sizeof(compressed));
		/*
		 * Unlike write_loose_object(), we do not have the entire
		 * buffer. If we get Z_BUF_ERROR due to too few input bytes,
		 * then we'll replenish them in the next input_stream->read()
		 * call when we loop.
		 */
	} while (ret == Z_OK || ret == Z_BUF_ERROR);

	if (stream.total_in != len + hdrlen)
		die(_("write stream object %ld != %"PRIuMAX), stream.total_in,
		    (uintmax_t)len + hdrlen);

	/*
	 * Common steps for write_loose_object and stream_loose_object to
	 * end writing loose oject:
	 *
	 *  - End the compression of zlib stream.
	 *  - Get the calculated oid.
	 */
	if (ret != Z_STREAM_END)
		die(_("unable to stream deflate new object (%d)"), ret);
	ret = end_loose_object_common(&c, &stream, oid);
	if (ret != Z_OK)
		die(_("deflateEnd on stream object failed (%d)"), ret);
	close_loose_object(fd, tmp_file.buf);

	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1)) {
		unlink_or_warn(tmp_file.buf);
		goto cleanup;
	}

	loose_object_path(the_repository, &filename, oid);

	/* We finally know the object path, and create the missing dir. */
	dirlen = directory_size(filename.buf);
	if (dirlen) {
		struct strbuf dir = STRBUF_INIT;
		strbuf_add(&dir, filename.buf, dirlen);

		if (mkdir_in_gitdir(dir.buf) && errno != EEXIST) {
			err = error_errno(_("unable to create directory %s"), dir.buf);
			strbuf_release(&dir);
			goto cleanup;
		}
		strbuf_release(&dir);
	}

	err = finalize_object_file(tmp_file.buf, filename.buf);
cleanup:
	strbuf_release(&tmp_file);
	strbuf_release(&filename);
	return err;
}

int write_object_file_flags(const void *buf, size_t len,
			    enum object_type type, struct object_id *oid,
			    unsigned flags)
{
	char hdr[MAX_HEADER_LEN];
	size_t hdrlen = sizeof(hdr);

	/* Normally if we have it in the pack then we do not bother writing
	 * it out into .git/objects/??/?{38} file.
	 */
	write_object_file_prepare(the_hash_algo, buf, len, type, oid, hdr,
				  &hdrlen);
	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
		return 0;
	return write_loose_object(oid, hdr, hdrlen, buf, len, 0, flags);
}

int write_object_file_literally(const void *buf, size_t len,
				const char *type, struct object_id *oid,
				unsigned flags)
{
	char *header;
	size_t hdrlen;
	int status = 0;

	/* type string, SP, %lu of the length plus NUL must fit this */
	hdrlen = strlen(type) + MAX_HEADER_LEN;
	header = xmalloc(hdrlen);
	write_object_file_prepare_literally(the_hash_algo, buf, len, type,
					    oid, header, &hdrlen);

	if (!(flags & HASH_WRITE_OBJECT))
		goto cleanup;
	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
		goto cleanup;
	status = write_loose_object(oid, header, hdrlen, buf, len, 0, 0);

cleanup:
	free(header);
	return status;
}

int force_object_loose(const struct object_id *oid, time_t mtime)
{
	void *buf;
	unsigned long len;
	struct object_info oi = OBJECT_INFO_INIT;
	enum object_type type;
	char hdr[MAX_HEADER_LEN];
	int hdrlen;
	int ret;

	if (has_loose_object(oid))
		return 0;
	oi.typep = &type;
	oi.sizep = &len;
	oi.contentp = &buf;
	if (oid_object_info_extended(the_repository, oid, &oi, 0))
		return error(_("cannot read object for %s"), oid_to_hex(oid));
	hdrlen = format_object_header(hdr, sizeof(hdr), type, len);
	ret = write_loose_object(oid, hdr, hdrlen, buf, len, mtime, 0);
	free(buf);

	return ret;
}

int has_object(struct repository *r, const struct object_id *oid,
	       unsigned flags)
{
	int quick = !(flags & HAS_OBJECT_RECHECK_PACKED);
	unsigned object_info_flags = OBJECT_INFO_SKIP_FETCH_OBJECT |
		(quick ? OBJECT_INFO_QUICK : 0);

	if (!startup_info->have_repository)
		return 0;
	return oid_object_info_extended(r, oid, NULL, object_info_flags) >= 0;
}

int repo_has_object_file_with_flags(struct repository *r,
				    const struct object_id *oid, int flags)
{
	if (!startup_info->have_repository)
		return 0;
	return oid_object_info_extended(r, oid, NULL, flags) >= 0;
}

int repo_has_object_file(struct repository *r,
			 const struct object_id *oid)
{
	return repo_has_object_file_with_flags(r, oid, 0);
}

/*
 * We can't use the normal fsck_error_function() for index_mem(),
 * because we don't yet have a valid oid for it to report. Instead,
 * report the minimal fsck error here, and rely on the caller to
 * give more context.
 */
static int hash_format_check_report(struct fsck_options *opts,
				     const struct object_id *oid,
				     enum object_type object_type,
				     enum fsck_msg_type msg_type,
				     enum fsck_msg_id msg_id,
				     const char *message)
{
	error(_("object fails fsck: %s"), message);
	return 1;
}

static int index_mem(struct index_state *istate,
		     struct object_id *oid, void *buf, size_t size,
		     enum object_type type,
		     const char *path, unsigned flags)
{
	int ret = 0;
	int re_allocated = 0;
	int write_object = flags & HASH_WRITE_OBJECT;

	if (!type)
		type = OBJ_BLOB;

	/*
	 * Convert blobs to git internal format
	 */
	if ((type == OBJ_BLOB) && path) {
		struct strbuf nbuf = STRBUF_INIT;
		if (convert_to_git(istate, path, buf, size, &nbuf,
				   get_conv_flags(flags))) {
			buf = strbuf_detach(&nbuf, &size);
			re_allocated = 1;
		}
	}
	if (flags & HASH_FORMAT_CHECK) {
		struct fsck_options opts = FSCK_OPTIONS_DEFAULT;

		opts.strict = 1;
		opts.error_func = hash_format_check_report;
		if (fsck_buffer(null_oid(), type, buf, size, &opts))
			die(_("refusing to create malformed object"));
		fsck_finish(&opts);
	}

	if (write_object)
		ret = write_object_file(buf, size, type, oid);
	else
		hash_object_file(the_hash_algo, buf, size, type, oid);
	if (re_allocated)
		free(buf);
	return ret;
}

static int index_stream_convert_blob(struct index_state *istate,
				     struct object_id *oid,
				     int fd,
				     const char *path,
				     unsigned flags)
{
	int ret = 0;
	const int write_object = flags & HASH_WRITE_OBJECT;
	struct strbuf sbuf = STRBUF_INIT;

	assert(path);
	assert(would_convert_to_git_filter_fd(istate, path));

	convert_to_git_filter_fd(istate, path, fd, &sbuf,
				 get_conv_flags(flags));

	if (write_object)
		ret = write_object_file(sbuf.buf, sbuf.len, OBJ_BLOB,
					oid);
	else
		hash_object_file(the_hash_algo, sbuf.buf, sbuf.len, OBJ_BLOB,
				 oid);
	strbuf_release(&sbuf);
	return ret;
}

static int index_pipe(struct index_state *istate, struct object_id *oid,
		      int fd, enum object_type type,
		      const char *path, unsigned flags)
{
	struct strbuf sbuf = STRBUF_INIT;
	int ret;

	if (strbuf_read(&sbuf, fd, 4096) >= 0)
		ret = index_mem(istate, oid, sbuf.buf, sbuf.len, type, path, flags);
	else
		ret = -1;
	strbuf_release(&sbuf);
	return ret;
}

#define SMALL_FILE_SIZE (32*1024)

static int index_core(struct index_state *istate,
		      struct object_id *oid, int fd, size_t size,
		      enum object_type type, const char *path,
		      unsigned flags)
{
	int ret;

	if (!size) {
		ret = index_mem(istate, oid, "", size, type, path, flags);
	} else if (size <= SMALL_FILE_SIZE) {
		char *buf = xmalloc(size);
		ssize_t read_result = read_in_full(fd, buf, size);
		if (read_result < 0)
			ret = error_errno(_("read error while indexing %s"),
					  path ? path : "<unknown>");
		else if (read_result != size)
			ret = error(_("short read while indexing %s"),
				    path ? path : "<unknown>");
		else
			ret = index_mem(istate, oid, buf, size, type, path, flags);
		free(buf);
	} else {
		void *buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
		ret = index_mem(istate, oid, buf, size, type, path, flags);
		munmap(buf, size);
	}
	return ret;
}

/*
 * This creates one packfile per large blob unless bulk-checkin
 * machinery is "plugged".
 *
 * This also bypasses the usual "convert-to-git" dance, and that is on
 * purpose. We could write a streaming version of the converting
 * functions and insert that before feeding the data to fast-import
 * (or equivalent in-core API described above). However, that is
 * somewhat complicated, as we do not know the size of the filter
 * result, which we need to know beforehand when writing a git object.
 * Since the primary motivation for trying to stream from the working
 * tree file and to avoid mmaping it in core is to deal with large
 * binary blobs, they generally do not want to get any conversion, and
 * callers should avoid this code path when filters are requested.
 */
static int index_stream(struct object_id *oid, int fd, size_t size,
			enum object_type type, const char *path,
			unsigned flags)
{
	return index_bulk_checkin(oid, fd, size, type, path, flags);
}

int index_fd(struct index_state *istate, struct object_id *oid,
	     int fd, struct stat *st,
	     enum object_type type, const char *path, unsigned flags)
{
	int ret;

	/*
	 * Call xsize_t() only when needed to avoid potentially unnecessary
	 * die() for large files.
	 */
	if (type == OBJ_BLOB && path && would_convert_to_git_filter_fd(istate, path))
		ret = index_stream_convert_blob(istate, oid, fd, path, flags);
	else if (!S_ISREG(st->st_mode))
		ret = index_pipe(istate, oid, fd, type, path, flags);
	else if (st->st_size <= big_file_threshold || type != OBJ_BLOB ||
		 (path && would_convert_to_git(istate, path)))
		ret = index_core(istate, oid, fd, xsize_t(st->st_size),
				 type, path, flags);
	else
		ret = index_stream(oid, fd, xsize_t(st->st_size), type, path,
				   flags);
	close(fd);
	return ret;
}

int index_path(struct index_state *istate, struct object_id *oid,
	       const char *path, struct stat *st, unsigned flags)
{
	int fd;
	struct strbuf sb = STRBUF_INIT;
	int rc = 0;

	switch (st->st_mode & S_IFMT) {
	case S_IFREG:
		fd = open(path, O_RDONLY);
		if (fd < 0)
			return error_errno("open(\"%s\")", path);
		if (index_fd(istate, oid, fd, st, OBJ_BLOB, path, flags) < 0)
			return error(_("%s: failed to insert into database"),
				     path);
		break;
	case S_IFLNK:
		if (strbuf_readlink(&sb, path, st->st_size))
			return error_errno("readlink(\"%s\")", path);
		if (!(flags & HASH_WRITE_OBJECT))
			hash_object_file(the_hash_algo, sb.buf, sb.len,
					 OBJ_BLOB, oid);
		else if (write_object_file(sb.buf, sb.len, OBJ_BLOB, oid))
			rc = error(_("%s: failed to insert into database"), path);
		strbuf_release(&sb);
		break;
	case S_IFDIR:
		return resolve_gitlink_ref(path, "HEAD", oid);
	default:
		return error(_("%s: unsupported file type"), path);
	}
	return rc;
}

int read_pack_header(int fd, struct pack_header *header)
{
	if (read_in_full(fd, header, sizeof(*header)) != sizeof(*header))
		/* "eof before pack header was fully read" */
		return PH_ERROR_EOF;

	if (header->hdr_signature != htonl(PACK_SIGNATURE))
		/* "protocol error (pack signature mismatch detected)" */
		return PH_ERROR_PACK_SIGNATURE;
	if (!pack_version_ok(header->hdr_version))
		/* "protocol error (pack version unsupported)" */
		return PH_ERROR_PROTOCOL;
	return 0;
}

void assert_oid_type(const struct object_id *oid, enum object_type expect)
{
	enum object_type type = oid_object_info(the_repository, oid, NULL);
	if (type < 0)
		die(_("%s is not a valid object"), oid_to_hex(oid));
	if (type != expect)
		die(_("%s is not a valid '%s' object"), oid_to_hex(oid),
		    type_name(expect));
}

int for_each_file_in_obj_subdir(unsigned int subdir_nr,
				struct strbuf *path,
				each_loose_object_fn obj_cb,
				each_loose_cruft_fn cruft_cb,
				each_loose_subdir_fn subdir_cb,
				void *data)
{
	size_t origlen, baselen;
	DIR *dir;
	struct dirent *de;
	int r = 0;
	struct object_id oid;

	if (subdir_nr > 0xff)
		BUG("invalid loose object subdirectory: %x", subdir_nr);

	origlen = path->len;
	strbuf_complete(path, '/');
	strbuf_addf(path, "%02x", subdir_nr);

	dir = opendir(path->buf);
	if (!dir) {
		if (errno != ENOENT)
			r = error_errno(_("unable to open %s"), path->buf);
		strbuf_setlen(path, origlen);
		return r;
	}

	oid.hash[0] = subdir_nr;
	strbuf_addch(path, '/');
	baselen = path->len;

	while ((de = readdir_skip_dot_and_dotdot(dir))) {
		size_t namelen;

		namelen = strlen(de->d_name);
		strbuf_setlen(path, baselen);
		strbuf_add(path, de->d_name, namelen);
		if (namelen == the_hash_algo->hexsz - 2 &&
		    !hex_to_bytes(oid.hash + 1, de->d_name,
				  the_hash_algo->rawsz - 1)) {
			oid_set_algo(&oid, the_hash_algo);
			if (obj_cb) {
				r = obj_cb(&oid, path->buf, data);
				if (r)
					break;
			}
			continue;
		}

		if (cruft_cb) {
			r = cruft_cb(de->d_name, path->buf, data);
			if (r)
				break;
		}
	}
	closedir(dir);

	strbuf_setlen(path, baselen - 1);
	if (!r && subdir_cb)
		r = subdir_cb(subdir_nr, path->buf, data);

	strbuf_setlen(path, origlen);

	return r;
}

int for_each_loose_file_in_objdir_buf(struct strbuf *path,
			    each_loose_object_fn obj_cb,
			    each_loose_cruft_fn cruft_cb,
			    each_loose_subdir_fn subdir_cb,
			    void *data)
{
	int r = 0;
	int i;

	for (i = 0; i < 256; i++) {
		r = for_each_file_in_obj_subdir(i, path, obj_cb, cruft_cb,
						subdir_cb, data);
		if (r)
			break;
	}

	return r;
}

int for_each_loose_file_in_objdir(const char *path,
				  each_loose_object_fn obj_cb,
				  each_loose_cruft_fn cruft_cb,
				  each_loose_subdir_fn subdir_cb,
				  void *data)
{
	struct strbuf buf = STRBUF_INIT;
	int r;

	strbuf_addstr(&buf, path);
	r = for_each_loose_file_in_objdir_buf(&buf, obj_cb, cruft_cb,
					      subdir_cb, data);
	strbuf_release(&buf);

	return r;
}

int for_each_loose_object(each_loose_object_fn cb, void *data,
			  enum for_each_object_flags flags)
{
	struct object_directory *odb;

	prepare_alt_odb(the_repository);
	for (odb = the_repository->objects->odb; odb; odb = odb->next) {
		int r = for_each_loose_file_in_objdir(odb->path, cb, NULL,
						      NULL, data);
		if (r)
			return r;

		if (flags & FOR_EACH_OBJECT_LOCAL_ONLY)
			break;
	}

	return 0;
}

static int append_loose_object(const struct object_id *oid, const char *path,
			       void *data)
{
	oidtree_insert(data, oid);
	return 0;
}

struct oidtree *odb_loose_cache(struct object_directory *odb,
				  const struct object_id *oid)
{
	int subdir_nr = oid->hash[0];
	struct strbuf buf = STRBUF_INIT;
	size_t word_bits = bitsizeof(odb->loose_objects_subdir_seen[0]);
	size_t word_index = subdir_nr / word_bits;
	size_t mask = (size_t)1u << (subdir_nr % word_bits);
	uint32_t *bitmap;

	if (subdir_nr < 0 ||
	    subdir_nr >= bitsizeof(odb->loose_objects_subdir_seen))
		BUG("subdir_nr out of range");

	bitmap = &odb->loose_objects_subdir_seen[word_index];
	if (*bitmap & mask)
		return odb->loose_objects_cache;
	if (!odb->loose_objects_cache) {
		ALLOC_ARRAY(odb->loose_objects_cache, 1);
		oidtree_init(odb->loose_objects_cache);
	}
	strbuf_addstr(&buf, odb->path);
	for_each_file_in_obj_subdir(subdir_nr, &buf,
				    append_loose_object,
				    NULL, NULL,
				    odb->loose_objects_cache);
	*bitmap |= mask;
	strbuf_release(&buf);
	return odb->loose_objects_cache;
}

void odb_loose_cache_add_new_oid(struct object_directory *odb,
				 const struct object_id *oid)
{
	struct oidtree *cache = odb_loose_cache(odb, oid);
	append_loose_object(oid, NULL, cache);
}

void odb_clear_loose_cache(struct object_directory *odb)
{
	oidtree_clear(odb->loose_objects_cache);
	FREE_AND_NULL(odb->loose_objects_cache);
	memset(&odb->loose_objects_subdir_seen, 0,
	       sizeof(odb->loose_objects_subdir_seen));
}

static int check_stream_oid(git_zstream *stream,
			    const char *hdr,
			    unsigned long size,
			    const char *path,
			    const struct object_id *expected_oid)
{
	git_hash_ctx c;
	struct object_id real_oid;
	unsigned char buf[4096];
	unsigned long total_read;
	int status = Z_OK;

	the_hash_algo->init_fn(&c);
	the_hash_algo->update_fn(&c, hdr, stream->total_out);

	/*
	 * We already read some bytes into hdr, but the ones up to the NUL
	 * do not count against the object's content size.
	 */
	total_read = stream->total_out - strlen(hdr) - 1;

	/*
	 * This size comparison must be "<=" to read the final zlib packets;
	 * see the comment in unpack_loose_rest for details.
	 */
	while (total_read <= size &&
	       (status == Z_OK ||
		(status == Z_BUF_ERROR && !stream->avail_out))) {
		stream->next_out = buf;
		stream->avail_out = sizeof(buf);
		if (size - total_read < stream->avail_out)
			stream->avail_out = size - total_read;
		status = git_inflate(stream, Z_FINISH);
		the_hash_algo->update_fn(&c, buf, stream->next_out - buf);
		total_read += stream->next_out - buf;
	}
	git_inflate_end(stream);

	if (status != Z_STREAM_END) {
		error(_("corrupt loose object '%s'"), oid_to_hex(expected_oid));
		return -1;
	}
	if (stream->avail_in) {
		error(_("garbage at end of loose object '%s'"),
		      oid_to_hex(expected_oid));
		return -1;
	}

	the_hash_algo->final_oid_fn(&real_oid, &c);
	if (!oideq(expected_oid, &real_oid)) {
		error(_("hash mismatch for %s (expected %s)"), path,
		      oid_to_hex(expected_oid));
		return -1;
	}

	return 0;
}

int read_loose_object(const char *path,
		      const struct object_id *expected_oid,
		      struct object_id *real_oid,
		      void **contents,
		      struct object_info *oi)
{
	int ret = -1;
	int fd;
	void *map = NULL;
	unsigned long mapsize;
	git_zstream stream;
	char hdr[MAX_HEADER_LEN];
	unsigned long *size = oi->sizep;

	fd = git_open(path);
	if (fd >= 0)
		map = map_fd(fd, path, &mapsize);
	if (!map) {
		error_errno(_("unable to mmap %s"), path);
		goto out;
	}

	if (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
				NULL) != ULHR_OK) {
		error(_("unable to unpack header of %s"), path);
		goto out;
	}

	if (parse_loose_header(hdr, oi) < 0) {
		error(_("unable to parse header of %s"), path);
		git_inflate_end(&stream);
		goto out;
	}

	if (*oi->typep == OBJ_BLOB && *size > big_file_threshold) {
		if (check_stream_oid(&stream, hdr, *size, path, expected_oid) < 0)
			goto out;
	} else {
		*contents = unpack_loose_rest(&stream, hdr, *size, expected_oid);
		if (!*contents) {
			error(_("unable to unpack contents of %s"), path);
			git_inflate_end(&stream);
			goto out;
		}
		hash_object_file_literally(the_repository->hash_algo,
					   *contents, *size,
					   oi->type_name->buf, real_oid);
		if (!oideq(expected_oid, real_oid))
			goto out;
	}

	ret = 0; /* everything checks out */

out:
	if (map)
		munmap(map, mapsize);
	return ret;
}