Merge branch 'ps/odb-source-loose'

The loose object source has been refactored into a proper `struct
odb_source`.

* ps/odb-source-loose:
  odb/source-loose: drop pointer to the "files" source
  odb/source-loose: stub out remaining callbacks
  odb/source-loose: wire up `write_object_stream()` callback
  object-file: refactor writing objects to use loose source
  odb/source-loose: wire up `write_object()` callback
  loose: refactor object map to operate on `struct odb_source_loose`
  odb/source-loose: wire up `freshen_object()` callback
  odb/source-loose: drop `odb_source_loose_has_object()`
  odb/source-loose: wire up `count_objects()` callback
  odb/source-loose: wire up `find_abbrev_len()` callback
  odb/source-loose: wire up `for_each_object()` callback
  odb/source-loose: wire up `read_object_stream()` callback
  odb/source-loose: wire up `read_object_info()` callback
  odb/source-loose: wire up `close()` callback
  odb/source-loose: wire up `reprepare()` callback
  odb/source-loose: start converting to a proper `struct odb_source`
  odb/source-loose: store pointer to "files" instead of generic source
  odb/source-loose: move loose source into "odb/" subsystem

15 files changed, 973 insertions, 870 deletions

diff --git a/Makefile b/Makefile
index b31ecb0756..0976a69b4c 100644
--- a/Makefile
+++ b/Makefile
@@ -1217,6 +1217,7 @@ LIB_OBJS += odb.o
 LIB_OBJS += odb/source.o
 LIB_OBJS += odb/source-files.o
 LIB_OBJS += odb/source-inmemory.o
+LIB_OBJS += odb/source-loose.o
 LIB_OBJS += odb/streaming.o
 LIB_OBJS += odb/transaction.o
 LIB_OBJS += oid-array.o
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 924c1d224c..2b64f8f733 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -890,8 +890,9 @@ static void batch_each_object(struct batch_options *opt,
 	 */
 	odb_prepare_alternates(the_repository->objects);
 	for (source = the_repository->objects->sources; source; source = source->next) {
-		int ret = odb_source_loose_for_each_object(source, NULL, batch_one_object_oi,
-							   &payload, &opts);
+		struct odb_source_files *files = odb_source_files_downcast(source);
+		int ret = odb_source_for_each_object(&files->loose->base, NULL, batch_one_object_oi,
+						     &payload, &opts);
 		if (ret)
 			break;
 	}
diff --git a/builtin/gc.c b/builtin/gc.c
index 84a66d3240..c26c93ee0f 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -466,6 +466,7 @@ out:
 
 static int too_many_loose_objects(int limit)
 {
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
 	/*
 	 * This is weird, but stems from legacy behaviour: the GC auto
 	 * threshold was always essentially interpreted as if it was rounded up
@@ -474,9 +475,8 @@ static int too_many_loose_objects(int limit)
 	int auto_threshold = DIV_ROUND_UP(limit, 256) * 256;
 	unsigned long loose_count;
 
-	if (odb_source_loose_count_objects(the_repository->objects->sources,
-					   ODB_COUNT_OBJECTS_APPROXIMATE,
-					   &loose_count) < 0)
+	if (odb_source_count_objects(&files->loose->base, ODB_COUNT_OBJECTS_APPROXIMATE,
+				     &loose_count) < 0)
 		return 0;
 
 	return loose_count > auto_threshold;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index fe9fbecb30..50675481e1 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1750,9 +1750,11 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 		 * skip the local object source.
 		 */
 		struct odb_source *source = the_repository->objects->sources->next;
-		for (; source; source = source->next)
-			if (odb_source_loose_has_object(source, oid))
+		for (; source; source = source->next) {
+			struct odb_source_files *files = odb_source_files_downcast(source);
+			if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0))
 				return 0;
+		}
 	}
 
 	/*
@@ -4135,9 +4137,11 @@ static void add_cruft_object_entry(const struct object_id *oid, enum object_type
 			struct odb_source *source = the_repository->objects->sources;
 			int found = 0;
 
-			for (; !found && source; source = source->next)
-				if (odb_source_loose_has_object(source, oid))
+			for (; !found && source; source = source->next) {
+				struct odb_source_files *files = odb_source_files_downcast(source);
+				if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0))
 					found = 1;
+			}
 
 			/*
 			 * If a traversed tree has a missing blob then we want
diff --git a/http-walker.c b/http-walker.c
index f252de089f..b58a3b2a92 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -539,8 +539,9 @@ static int fetch_object(struct walker *walker, const struct object_id *oid)
 	} else if (!oideq(&obj_req->oid, &req->real_oid)) {
 		ret = error("File %s has bad hash", hex);
 	} else if (req->rename < 0) {
+		struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
 		struct strbuf buf = STRBUF_INIT;
-		odb_loose_path(the_repository->objects->sources, &buf, &req->oid);
+		odb_loose_path(files->loose, &buf, &req->oid);
 		ret = error("unable to write sha1 filename %s", buf.buf);
 		strbuf_release(&buf);
 	}
diff --git a/http.c b/http.c
index ea9b16861b..3fcc012233 100644
--- a/http.c
+++ b/http.c
@@ -2826,6 +2826,7 @@ static size_t fwrite_sha1_file(char *ptr, size_t eltsize, size_t nmemb,
 struct http_object_request *new_http_object_request(const char *base_url,
 						    const struct object_id *oid)
 {
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
 	char *hex = oid_to_hex(oid);
 	struct strbuf filename = STRBUF_INIT;
 	struct strbuf prevfile = STRBUF_INIT;
@@ -2840,7 +2841,7 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	oidcpy(&freq->oid, oid);
 	freq->localfile = -1;
 
-	odb_loose_path(the_repository->objects->sources, &filename, oid);
+	odb_loose_path(files->loose, &filename, oid);
 	strbuf_addf(&freq->tmpfile, "%s.temp", filename.buf);
 
 	strbuf_addf(&prevfile, "%s.prev", filename.buf);
@@ -2966,6 +2967,7 @@ void process_http_object_request(struct http_object_request *freq)
 
 int finish_http_object_request(struct http_object_request *freq)
 {
+	struct odb_source_files *files = odb_source_files_downcast(the_repository->objects->sources);
 	struct stat st;
 	struct strbuf filename = STRBUF_INIT;
 
@@ -2992,7 +2994,7 @@ int finish_http_object_request(struct http_object_request *freq)
 		unlink_or_warn(freq->tmpfile.buf);
 		return -1;
 	}
-	odb_loose_path(the_repository->objects->sources, &filename, &freq->oid);
+	odb_loose_path(files->loose, &filename, &freq->oid);
 	freq->rename = finalize_object_file(the_repository, freq->tmpfile.buf, filename.buf);
 	strbuf_release(&filename);
 
diff --git a/loose.c b/loose.c
index f7a3dd1a72..0b626c1b85 100644
--- a/loose.c
+++ b/loose.c
@@ -46,38 +46,36 @@ static int insert_oid_pair(kh_oid_map_t *map, const struct object_id *key, const
 	return 1;
 }
 
-static int insert_loose_map(struct odb_source *source,
+static int insert_loose_map(struct odb_source_loose *loose,
 			    const struct object_id *oid,
 			    const struct object_id *compat_oid)
 {
-	struct odb_source_files *files = odb_source_files_downcast(source);
-	struct loose_object_map *map = files->loose->map;
+	struct loose_object_map *map = loose->map;
 	int inserted = 0;
 
 	inserted |= insert_oid_pair(map->to_compat, oid, compat_oid);
 	inserted |= insert_oid_pair(map->to_storage, compat_oid, oid);
 	if (inserted)
-		oidtree_insert(files->loose->cache, compat_oid, NULL);
+		oidtree_insert(loose->cache, compat_oid, NULL);
 
 	return inserted;
 }
 
-static int load_one_loose_object_map(struct repository *repo, struct odb_source *source)
+static int load_one_loose_object_map(struct repository *repo, struct odb_source_loose *loose)
 {
-	struct odb_source_files *files = odb_source_files_downcast(source);
 	struct strbuf buf = STRBUF_INIT, path = STRBUF_INIT;
 	FILE *fp;
 
-	if (!files->loose->map)
-		loose_object_map_init(&files->loose->map);
-	if (!files->loose->cache) {
-		ALLOC_ARRAY(files->loose->cache, 1);
-		oidtree_init(files->loose->cache);
+	if (!loose->map)
+		loose_object_map_init(&loose->map);
+	if (!loose->cache) {
+		ALLOC_ARRAY(loose->cache, 1);
+		oidtree_init(loose->cache);
 	}
 
-	insert_loose_map(source, repo->hash_algo->empty_tree, repo->compat_hash_algo->empty_tree);
-	insert_loose_map(source, repo->hash_algo->empty_blob, repo->compat_hash_algo->empty_blob);
-	insert_loose_map(source, repo->hash_algo->null_oid, repo->compat_hash_algo->null_oid);
+	insert_loose_map(loose, repo->hash_algo->empty_tree, repo->compat_hash_algo->empty_tree);
+	insert_loose_map(loose, repo->hash_algo->empty_blob, repo->compat_hash_algo->empty_blob);
+	insert_loose_map(loose, repo->hash_algo->null_oid, repo->compat_hash_algo->null_oid);
 
 	repo_common_path_replace(repo, &path, "objects/loose-object-idx");
 	fp = fopen(path.buf, "rb");
@@ -97,7 +95,7 @@ static int load_one_loose_object_map(struct repository *repo, struct odb_source
 		    parse_oid_hex_algop(p, &compat_oid, &p, repo->compat_hash_algo) ||
 		    p != buf.buf + buf.len)
 			goto err;
-		insert_loose_map(source, &oid, &compat_oid);
+		insert_loose_map(loose, &oid, &compat_oid);
 	}
 
 	strbuf_release(&buf);
@@ -119,7 +117,8 @@ int repo_read_loose_object_map(struct repository *repo)
 	odb_prepare_alternates(repo->objects);
 
 	for (source = repo->objects->sources; source; source = source->next) {
-		if (load_one_loose_object_map(repo, source) < 0) {
+		struct odb_source_files *files = odb_source_files_downcast(source);
+		if (load_one_loose_object_map(repo, files->loose) < 0) {
 			return -1;
 		}
 	}
@@ -171,7 +170,7 @@ errout:
 	return -1;
 }
 
-static int write_one_object(struct odb_source *source,
+static int write_one_object(struct odb_source_loose *loose,
 			    const struct object_id *oid,
 			    const struct object_id *compat_oid)
 {
@@ -180,7 +179,7 @@ static int write_one_object(struct odb_source *source,
 	struct stat st;
 	struct strbuf buf = STRBUF_INIT, path = STRBUF_INIT;
 
-	strbuf_addf(&path, "%s/loose-object-idx", source->path);
+	strbuf_addf(&path, "%s/loose-object-idx", loose->base.path);
 	hold_lock_file_for_update_timeout(&lock, path.buf, LOCK_DIE_ON_ERROR, -1);
 
 	fd = open(path.buf, O_WRONLY | O_CREAT | O_APPEND, 0666);
@@ -196,7 +195,7 @@ static int write_one_object(struct odb_source *source,
 		goto errout;
 	if (close(fd))
 		goto errout;
-	adjust_shared_perm(source->odb->repo, path.buf);
+	adjust_shared_perm(loose->base.odb->repo, path.buf);
 	rollback_lock_file(&lock);
 	strbuf_release(&buf);
 	strbuf_release(&path);
@@ -210,18 +209,18 @@ errout:
 	return -1;
 }
 
-int repo_add_loose_object_map(struct odb_source *source,
+int repo_add_loose_object_map(struct odb_source_loose *loose,
 			      const struct object_id *oid,
 			      const struct object_id *compat_oid)
 {
 	int inserted = 0;
 
-	if (!should_use_loose_object_map(source->odb->repo))
+	if (!should_use_loose_object_map(loose->base.odb->repo))
 		return 0;
 
-	inserted = insert_loose_map(source, oid, compat_oid);
+	inserted = insert_loose_map(loose, oid, compat_oid);
 	if (inserted)
-		return write_one_object(source, oid, compat_oid);
+		return write_one_object(loose, oid, compat_oid);
 	return 0;
 }
 
diff --git a/loose.h b/loose.h
index 6af1702973..6c9b3f4571 100644
--- a/loose.h
+++ b/loose.h
@@ -4,7 +4,7 @@
 #include "khash.h"
 
 struct repository;
-struct odb_source;
+struct odb_source_loose;
 
 struct loose_object_map {
 	kh_oid_map_t *to_compat;
@@ -17,7 +17,7 @@ int repo_loose_object_map_oid(struct repository *repo,
 			      const struct object_id *src,
 			      const struct git_hash_algo *dest_algo,
 			      struct object_id *dest);
-int repo_add_loose_object_map(struct odb_source *source,
+int repo_add_loose_object_map(struct odb_source_loose *loose,
 			      const struct object_id *oid,
 			      const struct object_id *compat_oid);
 int repo_read_loose_object_map(struct repository *repo);
diff --git a/meson.build b/meson.build
index 064fe2e2f1..3247697f74 100644
--- a/meson.build
+++ b/meson.build
@@ -405,6 +405,7 @@ libgit_sources = [
   'odb/source.c',
   'odb/source-files.c',
   'odb/source-inmemory.c',
+  'odb/source-loose.c',
   'odb/streaming.c',
   'odb/transaction.c',
   'oid-array.c',
diff --git a/object-file.c b/object-file.c
index 90f995d000..bce941874e 100644
--- a/object-file.c
+++ b/object-file.c
@@ -22,7 +22,6 @@
 #include "odb.h"
 #include "odb/streaming.h"
 #include "odb/transaction.h"
-#include "oidtree.h"
 #include "pack.h"
 #include "packfile.h"
 #include "path.h"
@@ -31,12 +30,6 @@
 #include "tempfile.h"
 #include "tmp-objdir.h"
 
-/* The maximum size for an object header. */
-#define MAX_HEADER_LEN 32
-
-static struct oidtree *odb_source_loose_cache(struct odb_source *source,
-					      const struct object_id *oid);
-
 static int get_conv_flags(unsigned flags)
 {
 	if (flags & INDEX_RENORMALIZE)
@@ -61,14 +54,14 @@ static void fill_loose_path(struct strbuf *buf,
 	}
 }
 
-const char *odb_loose_path(struct odb_source *source,
+const char *odb_loose_path(struct odb_source_loose *loose,
 			   struct strbuf *buf,
 			   const struct object_id *oid)
 {
 	strbuf_reset(buf);
-	strbuf_addstr(buf, source->path);
+	strbuf_addstr(buf, loose->base.path);
 	strbuf_addch(buf, '/');
-	fill_loose_path(buf, oid, source->odb->repo->hash_algo);
+	fill_loose_path(buf, oid, loose->base.odb->repo->hash_algo);
 	return buf->buf;
 }
 
@@ -94,21 +87,6 @@ int check_and_freshen_file(const char *fn, int freshen)
 	return 1;
 }
 
-static int check_and_freshen_source(struct odb_source *source,
-				    const struct object_id *oid,
-				    int freshen)
-{
-	static struct strbuf path = STRBUF_INIT;
-	odb_loose_path(source, &path, oid);
-	return check_and_freshen_file(path.buf, freshen);
-}
-
-int odb_source_loose_has_object(struct odb_source *source,
-				const struct object_id *oid)
-{
-	return check_and_freshen_source(source, oid, 0);
-}
-
 int format_object_header(char *str, size_t size, enum object_type type,
 			 size_t objsize)
 {
@@ -165,34 +143,6 @@ int stream_object_signature(struct repository *r,
 }
 
 /*
- * Find "oid" as a loose object in given source, open the object and return its
- * file descriptor. Returns the file descriptor 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 open_loose_object(struct odb_source_loose *loose,
-			     const struct object_id *oid, const char **path)
-{
-	static struct strbuf buf = STRBUF_INIT;
-	int fd;
-
-	*path = odb_loose_path(loose->source, &buf, oid);
-	fd = git_open(*path);
-	if (fd >= 0)
-		return fd;
-
-	return -1;
-}
-
-static int quick_has_loose(struct odb_source_loose *loose,
-			   const struct object_id *oid)
-{
-	return !!oidtree_contains(odb_source_loose_cache(loose->source, oid), oid);
-}
-
-/*
  * Map and close the given loose object fd. The path argument is used for
  * error reporting.
  */
@@ -215,42 +165,11 @@ static void *map_fd(int fd, const char *path, unsigned long *size)
 	return map;
 }
 
-static void *odb_source_loose_map_object(struct odb_source *source,
-					 const struct object_id *oid,
-					 unsigned long *size)
-{
-	struct odb_source_files *files = odb_source_files_downcast(source);
-	const char *p;
-	int fd = open_loose_object(files->loose, oid, &p);
-
-	if (fd < 0)
-		return NULL;
-	return map_fd(fd, p, size);
-}
-
-enum unpack_loose_header_result {
-	ULHR_OK,
-	ULHR_BAD,
-	ULHR_TOO_LONG,
-};
-
-/**
- * unpack_loose_header() initializes the data stream needed to unpack
- * a loose object header.
- *
- * Returns:
- *
- * - ULHR_OK on success
- * - ULHR_BAD on error
- * - ULHR_TOO_LONG if the header was too long
- *
- * It will only parse up to MAX_HEADER_LEN bytes.
- */
-static enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
-							   unsigned char *map,
-							   unsigned long mapsize,
-							   void *buffer,
-							   unsigned long bufsiz)
+enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
+						    unsigned char *map,
+						    unsigned long mapsize,
+						    void *buffer,
+						    unsigned long bufsiz)
 {
 	int status;
 
@@ -280,9 +199,9 @@ static enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
 	return ULHR_TOO_LONG;
 }
 
-static void *unpack_loose_rest(git_zstream *stream,
-			       void *buffer, unsigned long size,
-			       const struct object_id *oid)
+void *unpack_loose_rest(git_zstream *stream,
+			void *buffer, unsigned long size,
+			const struct object_id *oid)
 {
 	size_t bytes = strlen(buffer) + 1, n;
 	unsigned char *buf = xmallocz(size);
@@ -340,7 +259,7 @@ static void *unpack_loose_rest(git_zstream *stream,
  * too permissive for what we want to check. So do an anal
  * object header parse by hand.
  */
-static int parse_loose_header(const char *hdr, struct object_info *oi)
+int parse_loose_header(const char *hdr, struct object_info *oi)
 {
 	const char *type_buf = hdr;
 	size_t size;
@@ -396,170 +315,6 @@ static int parse_loose_header(const char *hdr, struct object_info *oi)
 	return 0;
 }
 
-static int read_object_info_from_path(struct odb_source *source,
-				      const char *path,
-				      const struct object_id *oid,
-				      struct object_info *oi,
-				      enum object_info_flags flags)
-{
-	struct odb_source_files *files = odb_source_files_downcast(source);
-	int ret;
-	int fd;
-	unsigned long mapsize;
-	void *map = NULL;
-	git_zstream stream, *stream_to_end = NULL;
-	char hdr[MAX_HEADER_LEN];
-	unsigned long size_scratch;
-	enum object_type type_scratch;
-	struct stat st;
-
-	/*
-	 * 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 || (!oi->typep && !oi->sizep && !oi->contentp)) {
-		struct stat st;
-
-		if ((!oi || (!oi->disk_sizep && !oi->mtimep)) && (flags & OBJECT_INFO_QUICK)) {
-			ret = quick_has_loose(files->loose, oid) ? 0 : -1;
-			goto out;
-		}
-
-		if (lstat(path, &st) < 0) {
-			ret = -1;
-			goto out;
-		}
-
-		if (oi) {
-			if (oi->disk_sizep)
-				*oi->disk_sizep = st.st_size;
-			if (oi->mtimep)
-				*oi->mtimep = st.st_mtime;
-		}
-
-		ret = 0;
-		goto out;
-	}
-
-	fd = git_open(path);
-	if (fd < 0) {
-		if (errno != ENOENT)
-			error_errno(_("unable to open loose object %s"), oid_to_hex(oid));
-		ret = -1;
-		goto out;
-	}
-
-	if (fstat(fd, &st)) {
-		close(fd);
-		ret = -1;
-		goto out;
-	}
-
-	mapsize = xsize_t(st.st_size);
-	if (!mapsize) {
-		close(fd);
-		ret = error(_("object file %s is empty"), path);
-		goto out;
-	}
-
-	map = xmmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, fd, 0);
-	close(fd);
-	if (!map) {
-		ret = -1;
-		goto out;
-	}
-
-	if (oi->disk_sizep)
-		*oi->disk_sizep = mapsize;
-	if (oi->mtimep)
-		*oi->mtimep = st.st_mtime;
-
-	stream_to_end = &stream;
-
-	switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr))) {
-	case ULHR_OK:
-		if (!oi->sizep)
-			oi->sizep = &size_scratch;
-		if (!oi->typep)
-			oi->typep = &type_scratch;
-
-		if (parse_loose_header(hdr, oi) < 0) {
-			ret = error(_("unable to parse %s header"), oid_to_hex(oid));
-			goto corrupt;
-		}
-
-		if (*oi->typep < 0)
-			die(_("invalid object type"));
-
-		if (oi->contentp) {
-			*oi->contentp = unpack_loose_rest(&stream, hdr, *oi->sizep, oid);
-			if (!*oi->contentp) {
-				ret = -1;
-				goto corrupt;
-			}
-		}
-
-		break;
-	case ULHR_BAD:
-		ret = error(_("unable to unpack %s header"),
-			    oid_to_hex(oid));
-		goto corrupt;
-	case ULHR_TOO_LONG:
-		ret = error(_("header for %s too long, exceeds %d bytes"),
-			    oid_to_hex(oid), MAX_HEADER_LEN);
-		goto corrupt;
-	}
-
-	ret = 0;
-
-corrupt:
-	if (ret && (flags & OBJECT_INFO_DIE_IF_CORRUPT))
-		die(_("loose object %s (stored in %s) is corrupt"),
-		    oid_to_hex(oid), path);
-
-out:
-	if (stream_to_end)
-		git_inflate_end(stream_to_end);
-	if (map)
-		munmap(map, mapsize);
-	if (oi) {
-		if (oi->sizep == &size_scratch)
-			oi->sizep = NULL;
-		if (oi->typep == &type_scratch)
-			oi->typep = NULL;
-		if (oi->delta_base_oid)
-			oidclr(oi->delta_base_oid, source->odb->repo->hash_algo);
-		if (!ret)
-			oi->whence = OI_LOOSE;
-	}
-
-	return ret;
-}
-
-int odb_source_loose_read_object_info(struct odb_source *source,
-				      const struct object_id *oid,
-				      struct object_info *oi,
-				      enum object_info_flags flags)
-{
-	static struct strbuf buf = STRBUF_INIT;
-
-	/*
-	 * The second read shouldn't cause new loose objects to show up, unless
-	 * there was a race condition with a secondary process. We don't care
-	 * about this case though, so we simply skip reading loose objects a
-	 * second time.
-	 */
-	if (flags & OBJECT_INFO_SECOND_READ)
-		return -1;
-
-	odb_loose_path(source, &buf, oid);
-	return read_object_info_from_path(source, buf.buf, oid, oi, flags);
-}
-
 static void hash_object_body(const struct git_hash_algo *algo, struct git_hash_ctx *c,
 			     const void *buf, unsigned long len,
 			     struct object_id *oid,
@@ -571,10 +326,10 @@ static void hash_object_body(const struct git_hash_algo *algo, struct git_hash_c
 	git_hash_final_oid(oid, c);
 }
 
-static void write_object_file_prepare(const struct git_hash_algo *algo,
-				      const void *buf, unsigned long len,
-				      enum object_type type, struct object_id *oid,
-				      char *hdr, int *hdrlen)
+void write_object_file_prepare(const struct git_hash_algo *algo,
+			       const void *buf, unsigned long len,
+			       enum object_type type, struct object_id *oid,
+			       char *hdr, int *hdrlen)
 {
 	struct git_hash_ctx c;
 
@@ -820,14 +575,14 @@ static void flush_loose_object_transaction(struct odb_transaction_files *transac
 }
 
 /* Finalize a file on disk, and close it. */
-static void close_loose_object(struct odb_source *source,
+static void close_loose_object(struct odb_source_loose *loose,
 			       int fd, const char *filename)
 {
-	if (source->will_destroy)
+	if (loose->base.will_destroy)
 		goto out;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		fsync_loose_object_transaction(source->odb->transaction, fd, filename);
+		fsync_loose_object_transaction(loose->base.odb->transaction, fd, filename);
 	else if (fsync_object_files > 0)
 		fsync_or_die(fd, filename);
 	else
@@ -896,7 +651,7 @@ static int create_tmpfile(struct repository *repo,
  * Returns a "fd", which should later be provided to
  * end_loose_object_common().
  */
-static int start_loose_object_common(struct odb_source *source,
+static int start_loose_object_common(struct odb_source_loose *loose,
 				     struct strbuf *tmp_file,
 				     const char *filename, unsigned flags,
 				     git_zstream *stream,
@@ -904,18 +659,18 @@ static int start_loose_object_common(struct odb_source *source,
 				     struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
 				     char *hdr, int hdrlen)
 {
-	const struct git_hash_algo *algo = source->odb->repo->hash_algo;
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
+	const struct git_hash_algo *algo = loose->base.odb->repo->hash_algo;
+	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
 	int fd;
 
-	fd = create_tmpfile(source->odb->repo, tmp_file, filename);
+	fd = create_tmpfile(loose->base.odb->repo, tmp_file, filename);
 	if (fd < 0) {
 		if (flags & ODB_WRITE_OBJECT_SILENT)
 			return -1;
 		else if (errno == EACCES)
 			return error(_("insufficient permission for adding "
 				       "an object to repository database %s"),
-				     source->path);
+				     loose->base.path);
 		else
 			return error_errno(
 				_("unable to create temporary file"));
@@ -945,14 +700,14 @@ static int start_loose_object_common(struct odb_source *source,
  * Common steps for the inner git_deflate() loop for writing loose
  * objects. Returns what git_deflate() returns.
  */
-static int write_loose_object_common(struct odb_source *source,
+static int write_loose_object_common(struct odb_source_loose *loose,
 				     struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
 				     git_zstream *stream, const int flush,
 				     unsigned char *in0, const int fd,
 				     unsigned char *compressed,
 				     const size_t compressed_len)
 {
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
+	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
 	int ret;
 
 	ret = git_deflate(stream, flush ? Z_FINISH : 0);
@@ -973,12 +728,12 @@ static int write_loose_object_common(struct odb_source *source,
  * - End the compression of zlib stream.
  * - Get the calculated oid to "oid".
  */
-static int end_loose_object_common(struct odb_source *source,
+static int end_loose_object_common(struct odb_source_loose *loose,
 				   struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
 				   git_zstream *stream, struct object_id *oid,
 				   struct object_id *compat_oid)
 {
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
+	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
 	int ret;
 
 	ret = git_deflate_end_gently(stream);
@@ -991,10 +746,10 @@ static int end_loose_object_common(struct odb_source *source,
 	return Z_OK;
 }
 
-static int write_loose_object(struct odb_source *source,
-			      const struct object_id *oid, char *hdr,
-			      int hdrlen, const void *buf, unsigned long len,
-			      time_t mtime, unsigned flags)
+int write_loose_object(struct odb_source_loose *loose,
+		       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];
@@ -1005,11 +760,11 @@ static int write_loose_object(struct odb_source *source,
 	static struct strbuf filename = STRBUF_INIT;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		prepare_loose_object_transaction(source->odb->transaction);
+		prepare_loose_object_transaction(loose->base.odb->transaction);
 
-	odb_loose_path(source, &filename, oid);
+	odb_loose_path(loose, &filename, oid);
 
-	fd = start_loose_object_common(source, &tmp_file, filename.buf, flags,
+	fd = start_loose_object_common(loose, &tmp_file, filename.buf, flags,
 				       &stream, compressed, sizeof(compressed),
 				       &c, NULL, hdr, hdrlen);
 	if (fd < 0)
@@ -1021,14 +776,14 @@ static int write_loose_object(struct odb_source *source,
 	do {
 		unsigned char *in0 = stream.next_in;
 
-		ret = write_loose_object_common(source, &c, NULL, &stream, 1, in0, fd,
+		ret = write_loose_object_common(loose, &c, NULL, &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(source, &c, NULL, &stream, &parano_oid, NULL);
+	ret = end_loose_object_common(loose, &c, NULL, &stream, &parano_oid, NULL);
 	if (ret != Z_OK)
 		die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid),
 		    ret);
@@ -1036,7 +791,7 @@ static int write_loose_object(struct odb_source *source,
 		die(_("confused by unstable object source data for %s"),
 		    oid_to_hex(oid));
 
-	close_loose_object(source, fd, tmp_file.buf);
+	close_loose_object(loose, fd, tmp_file.buf);
 
 	if (mtime) {
 		struct utimbuf utb;
@@ -1047,21 +802,15 @@ static int write_loose_object(struct odb_source *source,
 			warning_errno(_("failed utime() on %s"), tmp_file.buf);
 	}
 
-	return finalize_object_file_flags(source->odb->repo, tmp_file.buf, filename.buf,
+	return finalize_object_file_flags(loose->base.odb->repo, tmp_file.buf, filename.buf,
 					  FOF_SKIP_COLLISION_CHECK);
 }
 
-int odb_source_loose_freshen_object(struct odb_source *source,
-				    const struct object_id *oid)
-{
-	return !!check_and_freshen_source(source, oid, 1);
-}
-
-int odb_source_loose_write_stream(struct odb_source *source,
+int odb_source_loose_write_stream(struct odb_source_loose *loose,
 				  struct odb_write_stream *in_stream, size_t len,
 				  struct object_id *oid)
 {
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
+	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
 	struct object_id compat_oid;
 	int fd, ret, err = 0, flush = 0;
 	unsigned char compressed[4096];
@@ -1075,10 +824,10 @@ int odb_source_loose_write_stream(struct odb_source *source,
 	int hdrlen;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		prepare_loose_object_transaction(source->odb->transaction);
+		prepare_loose_object_transaction(loose->base.odb->transaction);
 
 	/* Since oid is not determined, save tmp file to odb path. */
-	strbuf_addf(&filename, "%s/", source->path);
+	strbuf_addf(&filename, "%s/", loose->base.path);
 	hdrlen = format_object_header(hdr, sizeof(hdr), OBJ_BLOB, len);
 
 	/*
@@ -1089,7 +838,7 @@ int odb_source_loose_write_stream(struct odb_source *source,
 	 *  - Setup zlib stream for compression.
 	 *  - Start to feed header to zlib stream.
 	 */
-	fd = start_loose_object_common(source, &tmp_file, filename.buf, 0,
+	fd = start_loose_object_common(loose, &tmp_file, filename.buf, 0,
 				       &stream, compressed, sizeof(compressed),
 				       &c, &compat_c, hdr, hdrlen);
 	if (fd < 0) {
@@ -1117,7 +866,7 @@ int odb_source_loose_write_stream(struct odb_source *source,
 			if (in_stream->is_finished)
 				flush = 1;
 		}
-		ret = write_loose_object_common(source, &c, &compat_c, &stream, flush, in0, fd,
+		ret = write_loose_object_common(loose, &c, &compat_c, &stream, flush, in0, fd,
 						compressed, sizeof(compressed));
 		/*
 		 * Unlike write_loose_object(), we do not have the entire
@@ -1140,16 +889,16 @@ int odb_source_loose_write_stream(struct odb_source *source,
 	 */
 	if (ret != Z_STREAM_END)
 		die(_("unable to stream deflate new object (%d)"), ret);
-	ret = end_loose_object_common(source, &c, &compat_c, &stream, oid, &compat_oid);
+	ret = end_loose_object_common(loose, &c, &compat_c, &stream, oid, &compat_oid);
 	if (ret != Z_OK)
 		die(_("deflateEnd on stream object failed (%d)"), ret);
-	close_loose_object(source, fd, tmp_file.buf);
+	close_loose_object(loose, fd, tmp_file.buf);
 
-	if (odb_freshen_object(source->odb, oid)) {
+	if (odb_freshen_object(loose->base.odb, oid)) {
 		unlink_or_warn(tmp_file.buf);
 		goto cleanup;
 	}
-	odb_loose_path(source, &filename, oid);
+	odb_loose_path(loose, &filename, oid);
 
 	/* We finally know the object path, and create the missing dir. */
 	dirlen = directory_size(filename.buf);
@@ -1157,7 +906,7 @@ int odb_source_loose_write_stream(struct odb_source *source,
 		struct strbuf dir = STRBUF_INIT;
 		strbuf_add(&dir, filename.buf, dirlen);
 
-		if (safe_create_dir_in_gitdir(source->odb->repo, dir.buf) &&
+		if (safe_create_dir_in_gitdir(loose->base.odb->repo, dir.buf) &&
 		    errno != EEXIST) {
 			err = error_errno(_("unable to create directory %s"), dir.buf);
 			strbuf_release(&dir);
@@ -1166,60 +915,20 @@ int odb_source_loose_write_stream(struct odb_source *source,
 		strbuf_release(&dir);
 	}
 
-	err = finalize_object_file_flags(source->odb->repo, tmp_file.buf, filename.buf,
+	err = finalize_object_file_flags(loose->base.odb->repo, tmp_file.buf, filename.buf,
 					 FOF_SKIP_COLLISION_CHECK);
 	if (!err && compat)
-		err = repo_add_loose_object_map(source, oid, &compat_oid);
+		err = repo_add_loose_object_map(loose, oid, &compat_oid);
 cleanup:
 	strbuf_release(&tmp_file);
 	strbuf_release(&filename);
 	return err;
 }
 
-int odb_source_loose_write_object(struct odb_source *source,
-				  const void *buf, unsigned long len,
-				  enum object_type type, struct object_id *oid,
-				  struct object_id *compat_oid_in,
-				  enum odb_write_object_flags flags)
-{
-	const struct git_hash_algo *algo = source->odb->repo->hash_algo;
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
-	struct object_id compat_oid;
-	char hdr[MAX_HEADER_LEN];
-	int hdrlen = sizeof(hdr);
-
-	/* Generate compat_oid */
-	if (compat) {
-		if (compat_oid_in)
-			oidcpy(&compat_oid, compat_oid_in);
-		else if (type == OBJ_BLOB)
-			hash_object_file(compat, buf, len, type, &compat_oid);
-		else {
-			struct strbuf converted = STRBUF_INIT;
-			convert_object_file(source->odb->repo, &converted, algo, compat,
-					    buf, len, type, 0);
-			hash_object_file(compat, converted.buf, converted.len,
-					 type, &compat_oid);
-			strbuf_release(&converted);
-		}
-	}
-
-	/* 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(algo, buf, len, type, oid, hdr, &hdrlen);
-	if (odb_freshen_object(source->odb, oid))
-		return 0;
-	if (write_loose_object(source, oid, hdr, hdrlen, buf, len, 0, flags))
-		return -1;
-	if (compat)
-		return repo_add_loose_object_map(source, oid, &compat_oid);
-	return 0;
-}
-
 int force_object_loose(struct odb_source *source,
 		       const struct object_id *oid, time_t mtime)
 {
+	struct odb_source_files *files = odb_source_files_downcast(source);
 	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
 	void *buf;
 	unsigned long len;
@@ -1230,9 +939,11 @@ int force_object_loose(struct odb_source *source,
 	int hdrlen;
 	int ret;
 
-	for (struct odb_source *s = source->odb->sources; s; s = s->next)
-		if (odb_source_loose_has_object(s, oid))
+	for (struct odb_source *s = source->odb->sources; s; s = s->next) {
+		struct odb_source_files *files = odb_source_files_downcast(s);
+		if (!odb_source_read_object_info(&files->loose->base, oid, NULL, 0))
 			return 0;
+	}
 
 	oi.typep = &type;
 	oi.sizep = &len;
@@ -1245,9 +956,9 @@ int force_object_loose(struct odb_source *source,
 				     oid_to_hex(oid), compat->name);
 	}
 	hdrlen = format_object_header(hdr, sizeof(hdr), type, len);
-	ret = write_loose_object(source, oid, hdr, hdrlen, buf, len, mtime, 0);
+	ret = write_loose_object(files->loose, oid, hdr, hdrlen, buf, len, mtime, 0);
 	if (!ret && compat)
-		ret = repo_add_loose_object_map(source, oid, &compat_oid);
+		ret = repo_add_loose_object_map(files->loose, oid, &compat_oid);
 	free(buf);
 
 	return ret;
@@ -1741,13 +1452,13 @@ int read_pack_header(int fd, struct pack_header *header)
 	return 0;
 }
 
-static int for_each_file_in_obj_subdir(unsigned int subdir_nr,
-				       struct strbuf *path,
-				       const struct git_hash_algo *algop,
-				       each_loose_object_fn obj_cb,
-				       each_loose_cruft_fn cruft_cb,
-				       each_loose_subdir_fn subdir_cb,
-				       void *data)
+int for_each_file_in_obj_subdir(unsigned int subdir_nr,
+				struct strbuf *path,
+				const struct git_hash_algo *algop,
+				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;
@@ -1832,229 +1543,6 @@ int for_each_loose_file_in_source(struct odb_source *source,
 	return r;
 }
 
-struct for_each_object_wrapper_data {
-	struct odb_source *source;
-	const struct object_info *request;
-	odb_for_each_object_cb cb;
-	void *cb_data;
-};
-
-static int for_each_object_wrapper_cb(const struct object_id *oid,
-				      const char *path,
-				      void *cb_data)
-{
-	struct for_each_object_wrapper_data *data = cb_data;
-
-	if (data->request) {
-		struct object_info oi = *data->request;
-
-		if (read_object_info_from_path(data->source, path, oid, &oi, 0) < 0)
-			return -1;
-
-		return data->cb(oid, &oi, data->cb_data);
-	} else {
-		return data->cb(oid, NULL, data->cb_data);
-	}
-}
-
-static int for_each_prefixed_object_wrapper_cb(const struct object_id *oid,
-					       void *node_data UNUSED,
-					       void *cb_data)
-{
-	struct for_each_object_wrapper_data *data = cb_data;
-	if (data->request) {
-		struct object_info oi = *data->request;
-
-		if (odb_source_loose_read_object_info(data->source,
-						      oid, &oi, 0) < 0)
-			return -1;
-
-		return data->cb(oid, &oi, data->cb_data);
-	} else {
-		return data->cb(oid, NULL, data->cb_data);
-	}
-}
-
-int odb_source_loose_for_each_object(struct odb_source *source,
-				     const struct object_info *request,
-				     odb_for_each_object_cb cb,
-				     void *cb_data,
-				     const struct odb_for_each_object_options *opts)
-{
-	struct for_each_object_wrapper_data data = {
-		.source = source,
-		.request = request,
-		.cb = cb,
-		.cb_data = cb_data,
-	};
-
-	/* There are no loose promisor objects, so we can return immediately. */
-	if ((opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY))
-		return 0;
-	if ((opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY) && !source->local)
-		return 0;
-
-	if (opts->prefix)
-		return oidtree_each(odb_source_loose_cache(source, opts->prefix),
-				    opts->prefix, opts->prefix_hex_len,
-				    for_each_prefixed_object_wrapper_cb, &data);
-
-	return for_each_loose_file_in_source(source, for_each_object_wrapper_cb,
-					     NULL, NULL, &data);
-}
-
-static int count_loose_object(const struct object_id *oid UNUSED,
-			      struct object_info *oi UNUSED,
-			      void *payload)
-{
-	unsigned long *count = payload;
-	(*count)++;
-	return 0;
-}
-
-int odb_source_loose_count_objects(struct odb_source *source,
-				   enum odb_count_objects_flags flags,
-				   unsigned long *out)
-{
-	const unsigned hexsz = source->odb->repo->hash_algo->hexsz - 2;
-	char *path = NULL;
-	DIR *dir = NULL;
-	int ret;
-
-	if (flags & ODB_COUNT_OBJECTS_APPROXIMATE) {
-		unsigned long count = 0;
-		struct dirent *ent;
-
-		path = xstrfmt("%s/17", source->path);
-
-		dir = opendir(path);
-		if (!dir) {
-			if (errno == ENOENT) {
-				*out = 0;
-				ret = 0;
-				goto out;
-			}
-
-			ret = error_errno("cannot open object shard '%s'", path);
-			goto out;
-		}
-
-		while ((ent = readdir(dir)) != NULL) {
-			if (strspn(ent->d_name, "0123456789abcdef") != hexsz ||
-			    ent->d_name[hexsz] != '\0')
-				continue;
-			count++;
-		}
-
-		*out = count * 256;
-		ret = 0;
-	} else {
-		struct odb_for_each_object_options opts = { 0 };
-		*out = 0;
-		ret = odb_source_loose_for_each_object(source, NULL, count_loose_object,
-						       out, &opts);
-	}
-
-out:
-	if (dir)
-		closedir(dir);
-	free(path);
-	return ret;
-}
-
-struct find_abbrev_len_data {
-	const struct object_id *oid;
-	unsigned len;
-};
-
-static int find_abbrev_len_cb(const struct object_id *oid,
-			      struct object_info *oi UNUSED,
-			      void *cb_data)
-{
-	struct find_abbrev_len_data *data = cb_data;
-	unsigned len = oid_common_prefix_hexlen(oid, data->oid);
-	if (len != hash_algos[oid->algo].hexsz && len >= data->len)
-		data->len = len + 1;
-	return 0;
-}
-
-int odb_source_loose_find_abbrev_len(struct odb_source *source,
-				     const struct object_id *oid,
-				     unsigned min_len,
-				     unsigned *out)
-{
-	struct odb_for_each_object_options opts = {
-		.prefix = oid,
-		.prefix_hex_len = min_len,
-	};
-	struct find_abbrev_len_data data = {
-		.oid = oid,
-		.len = min_len,
-	};
-	int ret;
-
-	ret = odb_source_loose_for_each_object(source, NULL, find_abbrev_len_cb,
-					       &data, &opts);
-	*out = data.len;
-
-	return ret;
-}
-
-static int append_loose_object(const struct object_id *oid,
-			       const char *path UNUSED,
-			       void *data)
-{
-	oidtree_insert(data, oid, NULL);
-	return 0;
-}
-
-static struct oidtree *odb_source_loose_cache(struct odb_source *source,
-					      const struct object_id *oid)
-{
-	struct odb_source_files *files = odb_source_files_downcast(source);
-	int subdir_nr = oid->hash[0];
-	struct strbuf buf = STRBUF_INIT;
-	size_t word_bits = bitsizeof(files->loose->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 ||
-	    (size_t) subdir_nr >= bitsizeof(files->loose->subdir_seen))
-		BUG("subdir_nr out of range");
-
-	bitmap = &files->loose->subdir_seen[word_index];
-	if (*bitmap & mask)
-		return files->loose->cache;
-	if (!files->loose->cache) {
-		ALLOC_ARRAY(files->loose->cache, 1);
-		oidtree_init(files->loose->cache);
-	}
-	strbuf_addstr(&buf, source->path);
-	for_each_file_in_obj_subdir(subdir_nr, &buf,
-				    source->odb->repo->hash_algo,
-				    append_loose_object,
-				    NULL, NULL,
-				    files->loose->cache);
-	*bitmap |= mask;
-	strbuf_release(&buf);
-	return files->loose->cache;
-}
-
-static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
-{
-	oidtree_clear(loose->cache);
-	FREE_AND_NULL(loose->cache);
-	memset(&loose->subdir_seen, 0,
-	       sizeof(loose->subdir_seen));
-}
-
-void odb_source_loose_reprepare(struct odb_source *source)
-{
-	struct odb_source_files *files = odb_source_files_downcast(source);
-	odb_source_loose_clear_cache(files->loose);
-}
-
 static int check_stream_oid(git_zstream *stream,
 			    const char *hdr,
 			    unsigned long size,
@@ -2204,155 +1692,3 @@ struct odb_transaction *odb_transaction_files_begin(struct odb_source *source)
 
 	return &transaction->base;
 }
-
-struct odb_source_loose *odb_source_loose_new(struct odb_source *source)
-{
-	struct odb_source_loose *loose;
-	CALLOC_ARRAY(loose, 1);
-	loose->source = source;
-	return loose;
-}
-
-void odb_source_loose_free(struct odb_source_loose *loose)
-{
-	if (!loose)
-		return;
-	odb_source_loose_clear_cache(loose);
-	loose_object_map_clear(&loose->map);
-	free(loose);
-}
-
-struct odb_loose_read_stream {
-	struct odb_read_stream base;
-	git_zstream z;
-	enum {
-		ODB_LOOSE_READ_STREAM_INUSE,
-		ODB_LOOSE_READ_STREAM_DONE,
-		ODB_LOOSE_READ_STREAM_ERROR,
-	} z_state;
-	void *mapped;
-	unsigned long mapsize;
-	char hdr[32];
-	int hdr_avail;
-	int hdr_used;
-};
-
-static ssize_t read_istream_loose(struct odb_read_stream *_st, char *buf, size_t sz)
-{
-	struct odb_loose_read_stream *st =
-		container_of(_st, struct odb_loose_read_stream, base);
-	size_t total_read = 0;
-
-	switch (st->z_state) {
-	case ODB_LOOSE_READ_STREAM_DONE:
-		return 0;
-	case ODB_LOOSE_READ_STREAM_ERROR:
-		return -1;
-	default:
-		break;
-	}
-
-	if (st->hdr_used < st->hdr_avail) {
-		size_t to_copy = st->hdr_avail - st->hdr_used;
-		if (sz < to_copy)
-			to_copy = sz;
-		memcpy(buf, st->hdr + st->hdr_used, to_copy);
-		st->hdr_used += to_copy;
-		total_read += to_copy;
-	}
-
-	while (total_read < sz) {
-		int status;
-
-		st->z.next_out = (unsigned char *)buf + total_read;
-		st->z.avail_out = sz - total_read;
-		status = git_inflate(&st->z, Z_FINISH);
-
-		total_read = st->z.next_out - (unsigned char *)buf;
-
-		if (status == Z_STREAM_END) {
-			git_inflate_end(&st->z);
-			st->z_state = ODB_LOOSE_READ_STREAM_DONE;
-			break;
-		}
-		if (status != Z_OK && (status != Z_BUF_ERROR || total_read < sz)) {
-			git_inflate_end(&st->z);
-			st->z_state = ODB_LOOSE_READ_STREAM_ERROR;
-			return -1;
-		}
-	}
-	return total_read;
-}
-
-static int close_istream_loose(struct odb_read_stream *_st)
-{
-	struct odb_loose_read_stream *st =
-		container_of(_st, struct odb_loose_read_stream, base);
-
-	if (st->z_state == ODB_LOOSE_READ_STREAM_INUSE)
-		git_inflate_end(&st->z);
-	munmap(st->mapped, st->mapsize);
-	return 0;
-}
-
-int odb_source_loose_read_object_stream(struct odb_read_stream **out,
-					struct odb_source *source,
-					const struct object_id *oid)
-{
-	struct object_info oi = OBJECT_INFO_INIT;
-	struct odb_loose_read_stream *st;
-	unsigned long mapsize;
-	unsigned long size_ul;
-	void *mapped;
-
-	mapped = odb_source_loose_map_object(source, oid, &mapsize);
-	if (!mapped)
-		return -1;
-
-	/*
-	 * Note: we must allocate this structure early even though we may still
-	 * fail. This is because we need to initialize the zlib stream, and it
-	 * is not possible to copy the stream around after the fact because it
-	 * has self-referencing pointers.
-	 */
-	CALLOC_ARRAY(st, 1);
-
-	switch (unpack_loose_header(&st->z, mapped, mapsize, st->hdr,
-				    sizeof(st->hdr))) {
-	case ULHR_OK:
-		break;
-	case ULHR_BAD:
-	case ULHR_TOO_LONG:
-		goto error;
-	}
-
-	/*
-	 * object_info.sizep is unsigned long* (32-bit on Windows), but
-	 * st->base.size is size_t (64-bit). Use temporary variable.
-	 * Note: loose objects >4GB would still truncate here, but such
-	 * large loose objects are uncommon (they'd normally be packed).
-	 */
-	oi.sizep = &size_ul;
-	oi.typep = &st->base.type;
-
-	if (parse_loose_header(st->hdr, &oi) < 0 || st->base.type < 0)
-		goto error;
-	st->base.size = size_ul;
-
-	st->mapped = mapped;
-	st->mapsize = mapsize;
-	st->hdr_used = strlen(st->hdr) + 1;
-	st->hdr_avail = st->z.total_out;
-	st->z_state = ODB_LOOSE_READ_STREAM_INUSE;
-	st->base.close = close_istream_loose;
-	st->base.read = read_istream_loose;
-
-	*out = &st->base;
-
-	return 0;
-error:
-	git_inflate_end(&st->z);
-	munmap(mapped, mapsize);
-	free(st);
-	return -1;
-}
diff --git a/object-file.h b/object-file.h
index 5241b8dd5c..528c4e6e69 100644
--- a/object-file.h
+++ b/object-file.h
@@ -4,6 +4,10 @@
 #include "git-zlib.h"
 #include "object.h"
 #include "odb.h"
+#include "odb/source-loose.h"
+
+/* The maximum size for an object header. */
+#define MAX_HEADER_LEN 32
 
 struct index_state;
 
@@ -17,61 +21,19 @@ int index_fd(struct index_state *istate, struct object_id *oid, int fd, struct s
 int index_path(struct index_state *istate, struct object_id *oid, const char *path, struct stat *st, unsigned flags);
 
 struct object_info;
-struct odb_read_stream;
 struct odb_source;
 
-struct odb_source_loose {
-	struct odb_source *source;
-
-	/*
-	 * Used to store the results of readdir(3) calls when we are OK
-	 * sacrificing accuracy due to races for speed. That includes
-	 * object existence with OBJECT_INFO_QUICK, as well as
-	 * our search for unique abbreviated hashes. Don't use it for tasks
-	 * requiring greater accuracy!
-	 *
-	 * Be sure to call odb_load_loose_cache() before using.
-	 */
-	uint32_t subdir_seen[8]; /* 256 bits */
-	struct oidtree *cache;
-
-	/* Map between object IDs for loose objects. */
-	struct loose_object_map *map;
-};
-
-struct odb_source_loose *odb_source_loose_new(struct odb_source *source);
-void odb_source_loose_free(struct odb_source_loose *loose);
-
-/* Reprepare the loose source by emptying the loose object cache. */
-void odb_source_loose_reprepare(struct odb_source *source);
-
-int odb_source_loose_read_object_info(struct odb_source *source,
-				      const struct object_id *oid,
-				      struct object_info *oi,
-				      enum object_info_flags flags);
-
-int odb_source_loose_read_object_stream(struct odb_read_stream **out,
-					struct odb_source *source,
-					const struct object_id *oid);
-
 /*
- * Return true iff an object database source has a loose object
- * with the specified name.  This function does not respect replace
- * references.
+ * Write the given stream into the loose object source. The only difference
+ * from the generic implementation of this function is that we don't perform an
+ * object existence check here.
+ *
+ * TODO: We should stop exposing this function altogether and move it into
+ * "odb/source-loose.c". This requires a couple of refactorings though to make
+ * `force_object_loose()` generic and is thus postponed to a later point in
+ * time.
  */
-int odb_source_loose_has_object(struct odb_source *source,
-				const struct object_id *oid);
-
-int odb_source_loose_freshen_object(struct odb_source *source,
-				    const struct object_id *oid);
-
-int odb_source_loose_write_object(struct odb_source *source,
-				  const void *buf, unsigned long len,
-				  enum object_type type, struct object_id *oid,
-				  struct object_id *compat_oid_in,
-				  enum odb_write_object_flags flags);
-
-int odb_source_loose_write_stream(struct odb_source *source,
+int odb_source_loose_write_stream(struct odb_source_loose *source,
 				  struct odb_write_stream *stream, size_t len,
 				  struct object_id *oid);
 
@@ -79,7 +41,7 @@ int odb_source_loose_write_stream(struct odb_source *source,
  * Put in `buf` the name of the file in the local object database that
  * would be used to store a loose object with the specified oid.
  */
-const char *odb_loose_path(struct odb_source *source,
+const char *odb_loose_path(struct odb_source_loose *source,
 			   struct strbuf *buf,
 			   const struct object_id *oid);
 
@@ -119,45 +81,13 @@ int for_each_loose_file_in_source(struct odb_source *source,
 				  each_loose_cruft_fn cruft_cb,
 				  each_loose_subdir_fn subdir_cb,
 				  void *data);
-
-/*
- * Iterate through all loose objects in the given object database source and
- * invoke the callback function for each of them. If an object info request is
- * given, then the object info will be read for every individual object and
- * passed to the callback as if `odb_source_loose_read_object_info()` was
- * called for the object.
- */
-int odb_source_loose_for_each_object(struct odb_source *source,
-				     const struct object_info *request,
-				     odb_for_each_object_cb cb,
-				     void *cb_data,
-				     const struct odb_for_each_object_options *opts);
-
-/*
- * Count the number of loose objects in this source.
- *
- * The object count is approximated by opening a single sharding directory for
- * loose objects and scanning its contents. The result is then extrapolated by
- * 256. This should generally work as a reasonable estimate given that the
- * object hash is supposed to be indistinguishable from random.
- *
- * Returns 0 on success, a negative error code otherwise.
- */
-int odb_source_loose_count_objects(struct odb_source *source,
-				   enum odb_count_objects_flags flags,
-				   unsigned long *out);
-
-/*
- * Find the shortest unique prefix for the given object ID, where `min_len` is
- * the minimum length that the prefix should have.
- *
- * Returns 0 on success, in which case the computed length will be written to
- * `out`. Otherwise, a negative error code is returned.
- */
-int odb_source_loose_find_abbrev_len(struct odb_source *source,
-				     const struct object_id *oid,
-				     unsigned min_len,
-				     unsigned *out);
+int for_each_file_in_obj_subdir(unsigned int subdir_nr,
+				struct strbuf *path,
+				const struct git_hash_algo *algop,
+				each_loose_object_fn obj_cb,
+				each_loose_cruft_fn cruft_cb,
+				each_loose_subdir_fn subdir_cb,
+				void *data);
 
 /**
  * format_object_header() is a thin wrapper around s xsnprintf() that
@@ -203,6 +133,14 @@ int finalize_object_file_flags(struct repository *repo,
 void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 		      unsigned long len, enum object_type type,
 		      struct object_id *oid);
+void write_object_file_prepare(const struct git_hash_algo *algo,
+			       const void *buf, unsigned long len,
+			       enum object_type type, struct object_id *oid,
+			       char *hdr, int *hdrlen);
+int write_loose_object(struct odb_source_loose *loose,
+		       const struct object_id *oid, char *hdr,
+		       int hdrlen, const void *buf, unsigned long len,
+		       time_t mtime, unsigned flags);
 
 /* Helper to check and "touch" a file */
 int check_and_freshen_file(const char *fn, int freshen);
@@ -222,6 +160,35 @@ int read_loose_object(struct repository *repo,
 		      void **contents,
 		      struct object_info *oi);
 
+enum unpack_loose_header_result {
+	ULHR_OK,
+	ULHR_BAD,
+	ULHR_TOO_LONG,
+};
+
+/**
+ * unpack_loose_header() initializes the data stream needed to unpack
+ * a loose object header.
+ *
+ * Returns:
+ *
+ * - ULHR_OK on success
+ * - ULHR_BAD on error
+ * - ULHR_TOO_LONG if the header was too long
+ *
+ * It will only parse up to MAX_HEADER_LEN bytes.
+ */
+enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
+						    unsigned char *map,
+						    unsigned long mapsize,
+						    void *buffer,
+						    unsigned long bufsiz);
+void *unpack_loose_rest(git_zstream *stream,
+			void *buffer, unsigned long size,
+			const struct object_id *oid);
+
+int parse_loose_header(const char *hdr, struct object_info *oi);
+
 struct odb_transaction;
 
 /*
diff --git a/odb/source-files.c b/odb/source-files.c
index b5abd20e97..5bdd042922 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -7,6 +7,7 @@
 #include "odb.h"
 #include "odb/source.h"
 #include "odb/source-files.h"
+#include "odb/source-loose.h"
 #include "packfile.h"
 #include "strbuf.h"
 #include "write-or-die.h"
@@ -27,7 +28,7 @@ static void odb_source_files_free(struct odb_source *source)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	chdir_notify_unregister(NULL, odb_source_files_reparent, files);
-	odb_source_loose_free(files->loose);
+	odb_source_free(&files->loose->base);
 	packfile_store_free(files->packed);
 	odb_source_release(&files->base);
 	free(files);
@@ -36,13 +37,14 @@ static void odb_source_files_free(struct odb_source *source)
 static void odb_source_files_close(struct odb_source *source)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
+	odb_source_close(&files->loose->base);
 	packfile_store_close(files->packed);
 }
 
 static void odb_source_files_reprepare(struct odb_source *source)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
-	odb_source_loose_reprepare(&files->base);
+	odb_source_reprepare(&files->loose->base);
 	packfile_store_reprepare(files->packed);
 }
 
@@ -54,7 +56,7 @@ static int odb_source_files_read_object_info(struct odb_source *source,
 	struct odb_source_files *files = odb_source_files_downcast(source);
 
 	if (!packfile_store_read_object_info(files->packed, oid, oi, flags) ||
-	    !odb_source_loose_read_object_info(source, oid, oi, flags))
+	    !odb_source_read_object_info(&files->loose->base, oid, oi, flags))
 		return 0;
 
 	return -1;
@@ -66,7 +68,7 @@ static int odb_source_files_read_object_stream(struct odb_read_stream **out,
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	if (!packfile_store_read_object_stream(out, files->packed, oid) ||
-	    !odb_source_loose_read_object_stream(out, source, oid))
+	    !odb_source_read_object_stream(out, &files->loose->base, oid))
 		return 0;
 	return -1;
 }
@@ -81,7 +83,7 @@ static int odb_source_files_for_each_object(struct odb_source *source,
 	int ret;
 
 	if (!(opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY)) {
-		ret = odb_source_loose_for_each_object(source, request, cb, cb_data, opts);
+		ret = odb_source_for_each_object(&files->loose->base, request, cb, cb_data, opts);
 		if (ret)
 			return ret;
 	}
@@ -108,7 +110,7 @@ static int odb_source_files_count_objects(struct odb_source *source,
 	if (!(flags & ODB_COUNT_OBJECTS_APPROXIMATE)) {
 		unsigned long loose_count;
 
-		ret = odb_source_loose_count_objects(source, flags, &loose_count);
+		ret = odb_source_count_objects(&files->loose->base, flags, &loose_count);
 		if (ret < 0)
 			goto out;
 
@@ -135,7 +137,7 @@ static int odb_source_files_find_abbrev_len(struct odb_source *source,
 	if (ret < 0)
 		goto out;
 
-	ret = odb_source_loose_find_abbrev_len(source, oid, len, &len);
+	ret = odb_source_find_abbrev_len(&files->loose->base, oid, len, &len);
 	if (ret < 0)
 		goto out;
 
@@ -151,7 +153,7 @@ static int odb_source_files_freshen_object(struct odb_source *source,
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
 	if (packfile_store_freshen_object(files->packed, oid) ||
-	    odb_source_loose_freshen_object(source, oid))
+	    odb_source_freshen_object(&files->loose->base, oid))
 		return 1;
 	return 0;
 }
@@ -163,8 +165,9 @@ static int odb_source_files_write_object(struct odb_source *source,
 					 struct object_id *compat_oid,
 					 enum odb_write_object_flags flags)
 {
-	return odb_source_loose_write_object(source, buf, len, type,
-					     oid, compat_oid, flags);
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	return odb_source_write_object(&files->loose->base, buf, len, type,
+				       oid, compat_oid, flags);
 }
 
 static int odb_source_files_write_object_stream(struct odb_source *source,
@@ -172,7 +175,8 @@ static int odb_source_files_write_object_stream(struct odb_source *source,
 						size_t len,
 						struct object_id *oid)
 {
-	return odb_source_loose_write_stream(source, stream, len, oid);
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	return odb_source_write_object_stream(&files->loose->base, stream, len, oid);
 }
 
 static int odb_source_files_begin_transaction(struct odb_source *source,
@@ -264,7 +268,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 
 	CALLOC_ARRAY(files, 1);
 	odb_source_init(&files->base, odb, ODB_SOURCE_FILES, path, local);
-	files->loose = odb_source_loose_new(&files->base);
+	files->loose = odb_source_loose_new(odb, path, local);
 	files->packed = packfile_store_new(&files->base);
 
 	files->base.free = odb_source_files_free;
diff --git a/odb/source-loose.c b/odb/source-loose.c
new file mode 100644
index 0000000000..7d7ea2fb84
--- /dev/null
+++ b/odb/source-loose.c
@@ -0,0 +1,736 @@
+#include "git-compat-util.h"
+#include "abspath.h"
+#include "chdir-notify.h"
+#include "gettext.h"
+#include "hex.h"
+#include "loose.h"
+#include "object-file.h"
+#include "object-file-convert.h"
+#include "odb.h"
+#include "odb/source-files.h"
+#include "odb/source-loose.h"
+#include "odb/streaming.h"
+#include "oidtree.h"
+#include "repository.h"
+#include "strbuf.h"
+
+static int append_loose_object(const struct object_id *oid,
+			       const char *path UNUSED,
+			       void *data)
+{
+	oidtree_insert(data, oid, NULL);
+	return 0;
+}
+
+static struct oidtree *odb_source_loose_cache(struct odb_source_loose *loose,
+					      const struct object_id *oid)
+{
+	int subdir_nr = oid->hash[0];
+	struct strbuf buf = STRBUF_INIT;
+	size_t word_bits = bitsizeof(loose->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 ||
+	    (size_t) subdir_nr >= bitsizeof(loose->subdir_seen))
+		BUG("subdir_nr out of range");
+
+	bitmap = &loose->subdir_seen[word_index];
+	if (*bitmap & mask)
+		return loose->cache;
+	if (!loose->cache) {
+		ALLOC_ARRAY(loose->cache, 1);
+		oidtree_init(loose->cache);
+	}
+	strbuf_addstr(&buf, loose->base.path);
+	for_each_file_in_obj_subdir(subdir_nr, &buf,
+				    loose->base.odb->repo->hash_algo,
+				    append_loose_object,
+				    NULL, NULL,
+				    loose->cache);
+	*bitmap |= mask;
+	strbuf_release(&buf);
+	return loose->cache;
+}
+
+static int quick_has_loose(struct odb_source_loose *loose,
+			   const struct object_id *oid)
+{
+	return !!oidtree_contains(odb_source_loose_cache(loose, oid), oid);
+}
+
+static int read_object_info_from_path(struct odb_source_loose *loose,
+				      const char *path,
+				      const struct object_id *oid,
+				      struct object_info *oi,
+				      enum object_info_flags flags)
+{
+	int ret;
+	int fd;
+	unsigned long mapsize;
+	void *map = NULL;
+	git_zstream stream, *stream_to_end = NULL;
+	char hdr[MAX_HEADER_LEN];
+	unsigned long size_scratch;
+	enum object_type type_scratch;
+	struct stat st;
+
+	/*
+	 * 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 || (!oi->typep && !oi->sizep && !oi->contentp)) {
+		struct stat st;
+
+		if ((!oi || (!oi->disk_sizep && !oi->mtimep)) && (flags & OBJECT_INFO_QUICK)) {
+			ret = quick_has_loose(loose, oid) ? 0 : -1;
+			goto out;
+		}
+
+		if (lstat(path, &st) < 0) {
+			ret = -1;
+			goto out;
+		}
+
+		if (oi) {
+			if (oi->disk_sizep)
+				*oi->disk_sizep = st.st_size;
+			if (oi->mtimep)
+				*oi->mtimep = st.st_mtime;
+		}
+
+		ret = 0;
+		goto out;
+	}
+
+	fd = git_open(path);
+	if (fd < 0) {
+		if (errno != ENOENT)
+			error_errno(_("unable to open loose object %s"), oid_to_hex(oid));
+		ret = -1;
+		goto out;
+	}
+
+	if (fstat(fd, &st)) {
+		close(fd);
+		ret = -1;
+		goto out;
+	}
+
+	mapsize = xsize_t(st.st_size);
+	if (!mapsize) {
+		close(fd);
+		ret = error(_("object file %s is empty"), path);
+		goto out;
+	}
+
+	map = xmmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (!map) {
+		ret = -1;
+		goto out;
+	}
+
+	if (oi->disk_sizep)
+		*oi->disk_sizep = mapsize;
+	if (oi->mtimep)
+		*oi->mtimep = st.st_mtime;
+
+	stream_to_end = &stream;
+
+	switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr))) {
+	case ULHR_OK:
+		if (!oi->sizep)
+			oi->sizep = &size_scratch;
+		if (!oi->typep)
+			oi->typep = &type_scratch;
+
+		if (parse_loose_header(hdr, oi) < 0) {
+			ret = error(_("unable to parse %s header"), oid_to_hex(oid));
+			goto corrupt;
+		}
+
+		if (*oi->typep < 0)
+			die(_("invalid object type"));
+
+		if (oi->contentp) {
+			*oi->contentp = unpack_loose_rest(&stream, hdr, *oi->sizep, oid);
+			if (!*oi->contentp) {
+				ret = -1;
+				goto corrupt;
+			}
+		}
+
+		break;
+	case ULHR_BAD:
+		ret = error(_("unable to unpack %s header"),
+			    oid_to_hex(oid));
+		goto corrupt;
+	case ULHR_TOO_LONG:
+		ret = error(_("header for %s too long, exceeds %d bytes"),
+			    oid_to_hex(oid), MAX_HEADER_LEN);
+		goto corrupt;
+	}
+
+	ret = 0;
+
+corrupt:
+	if (ret && (flags & OBJECT_INFO_DIE_IF_CORRUPT))
+		die(_("loose object %s (stored in %s) is corrupt"),
+		    oid_to_hex(oid), path);
+
+out:
+	if (stream_to_end)
+		git_inflate_end(stream_to_end);
+	if (map)
+		munmap(map, mapsize);
+	if (oi) {
+		if (oi->sizep == &size_scratch)
+			oi->sizep = NULL;
+		if (oi->typep == &type_scratch)
+			oi->typep = NULL;
+		if (oi->delta_base_oid)
+			oidclr(oi->delta_base_oid, loose->base.odb->repo->hash_algo);
+		if (!ret)
+			oi->whence = OI_LOOSE;
+	}
+
+	return ret;
+}
+
+static int odb_source_loose_read_object_info(struct odb_source *source,
+					     const struct object_id *oid,
+					     struct object_info *oi,
+					     enum object_info_flags flags)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	static struct strbuf buf = STRBUF_INIT;
+
+	/*
+	 * The second read shouldn't cause new loose objects to show up, unless
+	 * there was a race condition with a secondary process. We don't care
+	 * about this case though, so we simply skip reading loose objects a
+	 * second time.
+	 */
+	if (flags & OBJECT_INFO_SECOND_READ)
+		return -1;
+
+	odb_loose_path(loose, &buf, oid);
+	return read_object_info_from_path(loose, buf.buf, oid, oi, flags);
+}
+
+/*
+ * Find "oid" as a loose object in given source, open the object and return its
+ * file descriptor. Returns the file descriptor 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 open_loose_object().
+ */
+static int open_loose_object(struct odb_source_loose *loose,
+			     const struct object_id *oid, const char **path)
+{
+	static struct strbuf buf = STRBUF_INIT;
+	int fd;
+
+	*path = odb_loose_path(loose, &buf, oid);
+	fd = git_open(*path);
+	if (fd >= 0)
+		return fd;
+
+	return -1;
+}
+
+static void *odb_source_loose_map_object(struct odb_source_loose *loose,
+					 const struct object_id *oid,
+					 unsigned long *size)
+{
+	const char *p;
+	int fd = open_loose_object(loose, oid, &p);
+	void *map = NULL;
+	struct stat st;
+
+	if (fd < 0)
+		return NULL;
+
+	if (!fstat(fd, &st)) {
+		*size = xsize_t(st.st_size);
+		if (!*size) {
+			/* mmap() is forbidden on empty files */
+			error(_("object file %s is empty"), p);
+			goto out;
+		}
+
+		map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
+	}
+
+out:
+	close(fd);
+	return map;
+}
+
+struct odb_loose_read_stream {
+	struct odb_read_stream base;
+	git_zstream z;
+	enum {
+		ODB_LOOSE_READ_STREAM_INUSE,
+		ODB_LOOSE_READ_STREAM_DONE,
+		ODB_LOOSE_READ_STREAM_ERROR,
+	} z_state;
+	void *mapped;
+	unsigned long mapsize;
+	char hdr[32];
+	int hdr_avail;
+	int hdr_used;
+};
+
+static ssize_t read_istream_loose(struct odb_read_stream *_st, char *buf, size_t sz)
+{
+	struct odb_loose_read_stream *st =
+		container_of(_st, struct odb_loose_read_stream, base);
+	size_t total_read = 0;
+
+	switch (st->z_state) {
+	case ODB_LOOSE_READ_STREAM_DONE:
+		return 0;
+	case ODB_LOOSE_READ_STREAM_ERROR:
+		return -1;
+	default:
+		break;
+	}
+
+	if (st->hdr_used < st->hdr_avail) {
+		size_t to_copy = st->hdr_avail - st->hdr_used;
+		if (sz < to_copy)
+			to_copy = sz;
+		memcpy(buf, st->hdr + st->hdr_used, to_copy);
+		st->hdr_used += to_copy;
+		total_read += to_copy;
+	}
+
+	while (total_read < sz) {
+		int status;
+
+		st->z.next_out = (unsigned char *)buf + total_read;
+		st->z.avail_out = sz - total_read;
+		status = git_inflate(&st->z, Z_FINISH);
+
+		total_read = st->z.next_out - (unsigned char *)buf;
+
+		if (status == Z_STREAM_END) {
+			git_inflate_end(&st->z);
+			st->z_state = ODB_LOOSE_READ_STREAM_DONE;
+			break;
+		}
+		if (status != Z_OK && (status != Z_BUF_ERROR || total_read < sz)) {
+			git_inflate_end(&st->z);
+			st->z_state = ODB_LOOSE_READ_STREAM_ERROR;
+			return -1;
+		}
+	}
+	return total_read;
+}
+
+static int close_istream_loose(struct odb_read_stream *_st)
+{
+	struct odb_loose_read_stream *st =
+		container_of(_st, struct odb_loose_read_stream, base);
+
+	if (st->z_state == ODB_LOOSE_READ_STREAM_INUSE)
+		git_inflate_end(&st->z);
+	munmap(st->mapped, st->mapsize);
+	return 0;
+}
+
+static int odb_source_loose_read_object_stream(struct odb_read_stream **out,
+					       struct odb_source *source,
+					       const struct object_id *oid)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	struct object_info oi = OBJECT_INFO_INIT;
+	struct odb_loose_read_stream *st;
+	unsigned long mapsize;
+	unsigned long size_ul;
+	void *mapped;
+
+	mapped = odb_source_loose_map_object(loose, oid, &mapsize);
+	if (!mapped)
+		return -1;
+
+	/*
+	 * Note: we must allocate this structure early even though we may still
+	 * fail. This is because we need to initialize the zlib stream, and it
+	 * is not possible to copy the stream around after the fact because it
+	 * has self-referencing pointers.
+	 */
+	CALLOC_ARRAY(st, 1);
+
+	switch (unpack_loose_header(&st->z, mapped, mapsize, st->hdr,
+				    sizeof(st->hdr))) {
+	case ULHR_OK:
+		break;
+	case ULHR_BAD:
+	case ULHR_TOO_LONG:
+		goto error;
+	}
+
+	/*
+	 * object_info.sizep is unsigned long* (32-bit on Windows), but
+	 * st->base.size is size_t (64-bit). Use temporary variable.
+	 * Note: loose objects >4GB would still truncate here, but such
+	 * large loose objects are uncommon (they'd normally be packed).
+	 */
+	oi.sizep = &size_ul;
+	oi.typep = &st->base.type;
+
+	if (parse_loose_header(st->hdr, &oi) < 0 || st->base.type < 0)
+		goto error;
+	st->base.size = size_ul;
+
+	st->mapped = mapped;
+	st->mapsize = mapsize;
+	st->hdr_used = strlen(st->hdr) + 1;
+	st->hdr_avail = st->z.total_out;
+	st->z_state = ODB_LOOSE_READ_STREAM_INUSE;
+	st->base.close = close_istream_loose;
+	st->base.read = read_istream_loose;
+
+	*out = &st->base;
+
+	return 0;
+error:
+	git_inflate_end(&st->z);
+	munmap(mapped, mapsize);
+	free(st);
+	return -1;
+}
+
+struct for_each_object_wrapper_data {
+	struct odb_source_loose *loose;
+	const struct object_info *request;
+	odb_for_each_object_cb cb;
+	void *cb_data;
+};
+
+static int for_each_object_wrapper_cb(const struct object_id *oid,
+				      const char *path,
+				      void *cb_data)
+{
+	struct for_each_object_wrapper_data *data = cb_data;
+
+	if (data->request) {
+		struct object_info oi = *data->request;
+
+		if (read_object_info_from_path(data->loose, path, oid, &oi, 0) < 0)
+			return -1;
+
+		return data->cb(oid, &oi, data->cb_data);
+	} else {
+		return data->cb(oid, NULL, data->cb_data);
+	}
+}
+
+static int for_each_prefixed_object_wrapper_cb(const struct object_id *oid,
+					       void *node_data UNUSED,
+					       void *cb_data)
+{
+	struct for_each_object_wrapper_data *data = cb_data;
+	if (data->request) {
+		struct object_info oi = *data->request;
+
+		if (odb_source_read_object_info(&data->loose->base,
+						oid, &oi, 0) < 0)
+			return -1;
+
+		return data->cb(oid, &oi, data->cb_data);
+	} else {
+		return data->cb(oid, NULL, data->cb_data);
+	}
+}
+
+static int odb_source_loose_for_each_object(struct odb_source *source,
+					    const struct object_info *request,
+					    odb_for_each_object_cb cb,
+					    void *cb_data,
+					    const struct odb_for_each_object_options *opts)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	struct for_each_object_wrapper_data data = {
+		.loose = loose,
+		.request = request,
+		.cb = cb,
+		.cb_data = cb_data,
+	};
+
+	/* There are no loose promisor objects, so we can return immediately. */
+	if ((opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY))
+		return 0;
+	if ((opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY) && !source->local)
+		return 0;
+
+	if (opts->prefix)
+		return oidtree_each(odb_source_loose_cache(loose, opts->prefix),
+				    opts->prefix, opts->prefix_hex_len,
+				    for_each_prefixed_object_wrapper_cb, &data);
+
+	return for_each_loose_file_in_source(source, for_each_object_wrapper_cb,
+					     NULL, NULL, &data);
+}
+
+struct find_abbrev_len_data {
+	const struct object_id *oid;
+	unsigned len;
+};
+
+static int find_abbrev_len_cb(const struct object_id *oid,
+			      struct object_info *oi UNUSED,
+			      void *cb_data)
+{
+	struct find_abbrev_len_data *data = cb_data;
+	unsigned len = oid_common_prefix_hexlen(oid, data->oid);
+	if (len != hash_algos[oid->algo].hexsz && len >= data->len)
+		data->len = len + 1;
+	return 0;
+}
+
+static int odb_source_loose_find_abbrev_len(struct odb_source *source,
+					    const struct object_id *oid,
+					    unsigned min_len,
+					    unsigned *out)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	struct odb_for_each_object_options opts = {
+		.prefix = oid,
+		.prefix_hex_len = min_len,
+	};
+	struct find_abbrev_len_data data = {
+		.oid = oid,
+		.len = min_len,
+	};
+	int ret;
+
+	ret = odb_source_for_each_object(&loose->base, NULL, find_abbrev_len_cb,
+					 &data, &opts);
+	*out = data.len;
+
+	return ret;
+}
+
+static int count_loose_object(const struct object_id *oid UNUSED,
+			      struct object_info *oi UNUSED,
+			      void *payload)
+{
+	unsigned long *count = payload;
+	(*count)++;
+	return 0;
+}
+
+static int odb_source_loose_count_objects(struct odb_source *source,
+					  enum odb_count_objects_flags flags,
+					  unsigned long *out)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	const unsigned hexsz = source->odb->repo->hash_algo->hexsz - 2;
+	char *path = NULL;
+	DIR *dir = NULL;
+	int ret;
+
+	if (flags & ODB_COUNT_OBJECTS_APPROXIMATE) {
+		unsigned long count = 0;
+		struct dirent *ent;
+
+		path = xstrfmt("%s/17", source->path);
+
+		dir = opendir(path);
+		if (!dir) {
+			if (errno == ENOENT) {
+				*out = 0;
+				ret = 0;
+				goto out;
+			}
+
+			ret = error_errno("cannot open object shard '%s'", path);
+			goto out;
+		}
+
+		while ((ent = readdir(dir)) != NULL) {
+			if (strspn(ent->d_name, "0123456789abcdef") != hexsz ||
+			    ent->d_name[hexsz] != '\0')
+				continue;
+			count++;
+		}
+
+		*out = count * 256;
+		ret = 0;
+	} else {
+		struct odb_for_each_object_options opts = { 0 };
+		*out = 0;
+		ret = odb_source_for_each_object(&loose->base, NULL, count_loose_object,
+						 out, &opts);
+	}
+
+out:
+	if (dir)
+		closedir(dir);
+	free(path);
+	return ret;
+}
+
+static int odb_source_loose_freshen_object(struct odb_source *source,
+					   const struct object_id *oid)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	static struct strbuf path = STRBUF_INIT;
+	odb_loose_path(loose, &path, oid);
+	return !!check_and_freshen_file(path.buf, 1);
+}
+
+static int odb_source_loose_write_object(struct odb_source *source,
+					 const void *buf, unsigned long len,
+					 enum object_type type, struct object_id *oid,
+					 struct object_id *compat_oid_in,
+					 enum odb_write_object_flags flags)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	const struct git_hash_algo *algo = source->odb->repo->hash_algo;
+	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
+	struct object_id compat_oid;
+	char hdr[MAX_HEADER_LEN];
+	int hdrlen = sizeof(hdr);
+
+	/* Generate compat_oid */
+	if (compat) {
+		if (compat_oid_in)
+			oidcpy(&compat_oid, compat_oid_in);
+		else if (type == OBJ_BLOB)
+			hash_object_file(compat, buf, len, type, &compat_oid);
+		else {
+			struct strbuf converted = STRBUF_INIT;
+			convert_object_file(source->odb->repo, &converted, algo, compat,
+					    buf, len, type, 0);
+			hash_object_file(compat, converted.buf, converted.len,
+					 type, &compat_oid);
+			strbuf_release(&converted);
+		}
+	}
+
+	/* 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(algo, buf, len, type, oid, hdr, &hdrlen);
+	if (odb_freshen_object(source->odb, oid))
+		return 0;
+	if (write_loose_object(loose, oid, hdr, hdrlen, buf, len, 0, flags))
+		return -1;
+	if (compat)
+		return repo_add_loose_object_map(loose, oid, &compat_oid);
+	return 0;
+}
+
+static int odb_source_loose_write_object_stream(struct odb_source *source,
+						struct odb_write_stream *in_stream,
+						size_t len,
+						struct object_id *oid)
+{
+	/*
+	 * TODO: the implementation should be moved here, see the comment on
+	 * the called function in "object-file.h".
+	 */
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	return odb_source_loose_write_stream(loose, in_stream, len, oid);
+}
+
+static int odb_source_loose_begin_transaction(struct odb_source *source UNUSED,
+					      struct odb_transaction **out UNUSED)
+{
+	/* TODO: this is a known omission that we'll want to address eventually. */
+	return error("loose source does not support transactions");
+}
+
+static int odb_source_loose_read_alternates(struct odb_source *source UNUSED,
+					    struct strvec *out UNUSED)
+{
+	return 0;
+}
+
+static int odb_source_loose_write_alternate(struct odb_source *source UNUSED,
+					    const char *alternate UNUSED)
+{
+	return error("loose source does not support alternates");
+}
+
+static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
+{
+	oidtree_clear(loose->cache);
+	FREE_AND_NULL(loose->cache);
+	memset(&loose->subdir_seen, 0,
+	       sizeof(loose->subdir_seen));
+}
+
+static void odb_source_loose_reprepare(struct odb_source *source)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	odb_source_loose_clear_cache(loose);
+}
+
+static void odb_source_loose_close(struct odb_source *source UNUSED)
+{
+	/* Nothing to do. */
+}
+
+static void odb_source_loose_reparent(const char *name UNUSED,
+				      const char *old_cwd,
+				      const char *new_cwd,
+				      void *cb_data)
+{
+	struct odb_source_loose *loose = cb_data;
+	char *path = reparent_relative_path(old_cwd, new_cwd,
+					    loose->base.path);
+	free(loose->base.path);
+	loose->base.path = path;
+}
+
+static void odb_source_loose_free(struct odb_source *source)
+{
+	struct odb_source_loose *loose = odb_source_loose_downcast(source);
+	odb_source_loose_clear_cache(loose);
+	loose_object_map_clear(&loose->map);
+	chdir_notify_unregister(NULL, odb_source_loose_reparent, loose);
+	odb_source_release(&loose->base);
+	free(loose);
+}
+
+struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
+					      const char *path,
+					      bool local)
+{
+	struct odb_source_loose *loose;
+
+	CALLOC_ARRAY(loose, 1);
+	odb_source_init(&loose->base, odb, ODB_SOURCE_LOOSE, path, local);
+
+	loose->base.free = odb_source_loose_free;
+	loose->base.close = odb_source_loose_close;
+	loose->base.reprepare = odb_source_loose_reprepare;
+	loose->base.read_object_info = odb_source_loose_read_object_info;
+	loose->base.read_object_stream = odb_source_loose_read_object_stream;
+	loose->base.for_each_object = odb_source_loose_for_each_object;
+	loose->base.find_abbrev_len = odb_source_loose_find_abbrev_len;
+	loose->base.count_objects = odb_source_loose_count_objects;
+	loose->base.freshen_object = odb_source_loose_freshen_object;
+	loose->base.write_object = odb_source_loose_write_object;
+	loose->base.write_object_stream = odb_source_loose_write_object_stream;
+	loose->base.begin_transaction = odb_source_loose_begin_transaction;
+	loose->base.read_alternates = odb_source_loose_read_alternates;
+	loose->base.write_alternate = odb_source_loose_write_alternate;
+
+	if (!is_absolute_path(loose->base.path))
+		chdir_notify_register(NULL, odb_source_loose_reparent, loose);
+
+	return loose;
+}
diff --git a/odb/source-loose.h b/odb/source-loose.h
new file mode 100644
index 0000000000..6070aaf3ce
--- /dev/null
+++ b/odb/source-loose.h
@@ -0,0 +1,48 @@
+#ifndef ODB_SOURCE_LOOSE_H
+#define ODB_SOURCE_LOOSE_H
+
+#include "odb/source.h"
+
+struct odb_source_files;
+struct object_database;
+struct oidtree;
+
+/*
+ * An object database source that stores its objects in loose format, one
+ * file per object.
+ */
+struct odb_source_loose {
+	struct odb_source base;
+
+	/*
+	 * Used to store the results of readdir(3) calls when we are OK
+	 * sacrificing accuracy due to races for speed. That includes
+	 * object existence with OBJECT_INFO_QUICK, as well as
+	 * our search for unique abbreviated hashes. Don't use it for tasks
+	 * requiring greater accuracy!
+	 *
+	 * Be sure to call odb_load_loose_cache() before using.
+	 */
+	uint32_t subdir_seen[8]; /* 256 bits */
+	struct oidtree *cache;
+
+	/* Map between object IDs for loose objects. */
+	struct loose_object_map *map;
+};
+
+struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
+					      const char *path,
+					      bool local);
+
+/*
+ * Cast the given object database source to the loose backend. This will cause
+ * a BUG in case the source doesn't use this backend.
+ */
+static inline struct odb_source_loose *odb_source_loose_downcast(struct odb_source *source)
+{
+	if (source->type != ODB_SOURCE_LOOSE)
+		BUG("trying to downcast source of type '%d' to loose", source->type);
+	return container_of(source, struct odb_source_loose, base);
+}
+
+#endif
diff --git a/odb/source.h b/odb/source.h
index 0a440884e4..8bcb67787e 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -14,6 +14,9 @@ enum odb_source_type {
 	/* The "files" backend that uses loose objects and packfiles. */
 	ODB_SOURCE_FILES,
 
+	/* The "loose" backend that uses loose objects, only. */
+	ODB_SOURCE_LOOSE,
+
 	/* The "in-memory" backend that stores objects in memory. */
 	ODB_SOURCE_INMEMORY,
 };