Merge branch 'jt/packmigrate'

Code movement to make it easier to hack later.

* jt/packmigrate: (23 commits)
  pack: move for_each_packed_object()
  pack: move has_pack_index()
  pack: move has_sha1_pack()
  pack: move find_pack_entry() and make it global
  pack: move find_sha1_pack()
  pack: move find_pack_entry_one(), is_pack_valid()
  pack: move check_pack_index_ptr(), nth_packed_object_offset()
  pack: move nth_packed_object_{sha1,oid}
  pack: move clear_delta_base_cache(), packed_object_info(), unpack_entry()
  pack: move unpack_object_header()
  pack: move get_size_from_delta()
  pack: move unpack_object_header_buffer()
  pack: move {,re}prepare_packed_git and approximate_object_count
  pack: move install_packed_git()
  pack: move add_packed_git()
  pack: move unuse_pack()
  pack: move use_pack()
  pack: move pack-closing functions
  pack: move release_pack_memory()
  pack: move open_pack_index(), parse_pack_index()
  ...

37 files changed, 2081 insertions, 2014 deletions

diff --git a/Makefile b/Makefile
index ffab6f4568..f2bb7f2f63 100644
--- a/Makefile
+++ b/Makefile
@@ -817,6 +817,7 @@ LIB_OBJS += notes-merge.o
 LIB_OBJS += notes-utils.o
 LIB_OBJS += object.o
 LIB_OBJS += oidset.o
+LIB_OBJS += packfile.o
 LIB_OBJS += pack-bitmap.o
 LIB_OBJS += pack-bitmap-write.o
 LIB_OBJS += pack-check.o
diff --git a/builtin/am.c b/builtin/am.c
index 81095dae02..c369dd1dce 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -31,6 +31,7 @@
 #include "mailinfo.h"
 #include "apply.h"
 #include "string-list.h"
+#include "packfile.h"
 
 /**
  * Returns 1 if the file is empty or does not exist, 0 otherwise.
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 62c8cf0ebf..4ccbfaac31 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -12,6 +12,7 @@
 #include "streaming.h"
 #include "tree-walk.h"
 #include "sha1-array.h"
+#include "packfile.h"
 
 struct batch_options {
 	int enabled;
diff --git a/builtin/clone.c b/builtin/clone.c
index f7e17d2295..8d11b570a1 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -25,6 +25,7 @@
 #include "remote.h"
 #include "run-command.h"
 #include "connected.h"
+#include "packfile.h"
 
 /*
  * Overall FIXMEs:
diff --git a/builtin/count-objects.c b/builtin/count-objects.c
index 1d82e61f2a..33343818c8 100644
--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@@ -10,6 +10,7 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "quote.h"
+#include "packfile.h"
 
 static unsigned long garbage;
 static off_t size_garbage;
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 132e3224ed..225c734924 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -17,6 +17,7 @@
 #include "connected.h"
 #include "argv-array.h"
 #include "utf8.h"
+#include "packfile.h"
 
 static const char * const builtin_fetch_usage[] = {
 	N_("git fetch [<options>] [<repository> [<refspec>...]]"),
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 0ab13848a4..1e4c471b41 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -15,6 +15,7 @@
 #include "progress.h"
 #include "streaming.h"
 #include "decorate.h"
+#include "packfile.h"
 
 #define REACHABLE 0x0001
 #define SEEN      0x0002
diff --git a/builtin/gc.c b/builtin/gc.c
index e6b84475ae..3c78fcb9b1 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -19,6 +19,7 @@
 #include "sigchain.h"
 #include "argv-array.h"
 #include "commit.h"
+#include "packfile.h"
 
 #define FAILED_RUN "failed to run %s"
 
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 26828c1d82..f2be145e12 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -12,6 +12,7 @@
 #include "exec_cmd.h"
 #include "streaming.h"
 #include "thread-utils.h"
+#include "packfile.h"
 
 static const char index_pack_usage[] =
 "git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
diff --git a/builtin/merge.c b/builtin/merge.c
index cc57052993..7b7320dede 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -32,6 +32,7 @@
 #include "gpg-interface.h"
 #include "sequencer.h"
 #include "string-list.h"
+#include "packfile.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index c753e9237a..82ad6e0c81 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -25,6 +25,7 @@
 #include "sha1-array.h"
 #include "argv-array.h"
 #include "mru.h"
+#include "packfile.h"
 
 static const char *pack_usage[] = {
 	N_("git pack-objects --stdout [<options>...] [< <ref-list> | < <object-list>]"),
diff --git a/builtin/pack-redundant.c b/builtin/pack-redundant.c
index cb1df1c761..aaa8136322 100644
--- a/builtin/pack-redundant.c
+++ b/builtin/pack-redundant.c
@@ -7,6 +7,7 @@
 */
 
 #include "builtin.h"
+#include "packfile.h"
 
 #define BLKSIZE 512
 
diff --git a/builtin/prune-packed.c b/builtin/prune-packed.c
index 8f41f7c20e..419238171d 100644
--- a/builtin/prune-packed.c
+++ b/builtin/prune-packed.c
@@ -2,6 +2,7 @@
 #include "cache.h"
 #include "progress.h"
 #include "parse-options.h"
+#include "packfile.h"
 
 static const char * const prune_packed_usage[] = {
 	N_("git prune-packed [-n | --dry-run] [-q | --quiet]"),
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 14b6e09b42..52c63ebfdc 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -23,6 +23,7 @@
 #include "fsck.h"
 #include "tmp-objdir.h"
 #include "oidset.h"
+#include "packfile.h"
 
 static const char * const receive_pack_usage[] = {
 	N_("git receive-pack <git-dir>"),
diff --git a/bulk-checkin.c b/bulk-checkin.c
index 5be7ce5c73..9a1f6c49ab 100644
--- a/bulk-checkin.c
+++ b/bulk-checkin.c
@@ -6,6 +6,7 @@
 #include "csum-file.h"
 #include "pack.h"
 #include "strbuf.h"
+#include "packfile.h"
 
 static struct bulk_checkin_state {
 	unsigned plugged:1;
diff --git a/cache.h b/cache.h
index bd8802af0e..a916bc79e3 100644
--- a/cache.h
+++ b/cache.h
@@ -903,20 +903,6 @@ extern void check_repository_format(void);
 extern const char *sha1_file_name(const unsigned char *sha1);
 
 /*
- * Return the name of the (local) packfile with the specified sha1 in
- * its name.  The return value is a pointer to memory that is
- * overwritten each time this function is called.
- */
-extern char *sha1_pack_name(const unsigned char *sha1);
-
-/*
- * Return the name of the (local) pack index file with the specified
- * sha1 in its name.  The return value is a pointer to memory that is
- * overwritten each time this function is called.
- */
-extern char *sha1_pack_index_name(const unsigned char *sha1);
-
-/*
  * Return an abbreviated sha1 unique within this repository's object database.
  * The result will be at least `len` characters long, and will be NUL
  * terminated.
@@ -1201,15 +1187,10 @@ extern void *map_sha1_file(const unsigned char *sha1, unsigned long *size);
 extern int unpack_sha1_header(git_zstream *stream, unsigned char *map, unsigned long mapsize, void *buffer, unsigned long bufsiz);
 extern int parse_sha1_header(const char *hdr, unsigned long *sizep);
 
-/* global flag to enable extra checks when accessing packed objects */
-extern int do_check_packed_object_crc;
-
 extern int check_sha1_signature(const unsigned char *sha1, void *buf, unsigned long size, const char *type);
 
 extern int finalize_object_file(const char *tmpfile, const char *filename);
 
-extern int has_sha1_pack(const unsigned char *sha1);
-
 /*
  * Open the loose object at path, check its sha1, and return the contents,
  * type, and size. If the object is a blob, then "contents" may return NULL,
@@ -1245,8 +1226,6 @@ extern int has_object_file_with_flags(const struct object_id *oid, int flags);
  */
 extern int has_loose_object_nonlocal(const unsigned char *sha1);
 
-extern int has_pack_index(const unsigned char *sha1);
-
 extern void assert_sha1_type(const unsigned char *sha1, enum object_type expect);
 
 /* Helper to check and "touch" a file */
@@ -1619,29 +1598,6 @@ struct pack_entry {
 	struct packed_git *p;
 };
 
-extern struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path);
-
-/* A hook to report invalid files in pack directory */
-#define PACKDIR_FILE_PACK 1
-#define PACKDIR_FILE_IDX 2
-#define PACKDIR_FILE_GARBAGE 4
-extern void (*report_garbage)(unsigned seen_bits, const char *path);
-
-extern void prepare_packed_git(void);
-extern void reprepare_packed_git(void);
-extern void install_packed_git(struct packed_git *pack);
-
-/*
- * Give a rough count of objects in the repository. This sacrifices accuracy
- * for speed.
- */
-unsigned long approximate_object_count(void);
-
-extern struct packed_git *find_sha1_pack(const unsigned char *sha1,
-					 struct packed_git *packs);
-
-extern void pack_report(void);
-
 /*
  * Create a temporary file rooted in the object database directory, or
  * die on failure. The filename is taken from "pattern", which should have the
@@ -1651,15 +1607,6 @@ extern void pack_report(void);
 extern int odb_mkstemp(struct strbuf *template, const char *pattern);
 
 /*
- * Generate the filename to be used for a pack file with checksum "sha1" and
- * extension "ext". The result is written into the strbuf "buf", overwriting
- * any existing contents. A pointer to buf->buf is returned as a convenience.
- *
- * Example: odb_pack_name(out, sha1, "idx") => ".git/objects/pack/pack-1234..idx"
- */
-extern char *odb_pack_name(struct strbuf *buf, const unsigned char *sha1, const char *ext);
-
-/*
  * Create a pack .keep file named "name" (which should generally be the output
  * of odb_pack_name). Returns a file descriptor opened for writing, or -1 on
  * error.
@@ -1667,67 +1614,6 @@ extern char *odb_pack_name(struct strbuf *buf, const unsigned char *sha1, const
 extern int odb_pack_keep(const char *name);
 
 /*
- * mmap the index file for the specified packfile (if it is not
- * already mmapped).  Return 0 on success.
- */
-extern int open_pack_index(struct packed_git *);
-
-/*
- * munmap the index file for the specified packfile (if it is
- * currently mmapped).
- */
-extern void close_pack_index(struct packed_git *);
-
-extern unsigned char *use_pack(struct packed_git *, struct pack_window **, off_t, unsigned long *);
-extern void close_pack_windows(struct packed_git *);
-extern void close_all_packs(void);
-extern void unuse_pack(struct pack_window **);
-extern void clear_delta_base_cache(void);
-extern struct packed_git *add_packed_git(const char *path, size_t path_len, int local);
-
-/*
- * Make sure that a pointer access into an mmap'd index file is within bounds,
- * and can provide at least 8 bytes of data.
- *
- * Note that this is only necessary for variable-length segments of the file
- * (like the 64-bit extended offset table), as we compare the size to the
- * fixed-length parts when we open the file.
- */
-extern void check_pack_index_ptr(const struct packed_git *p, const void *ptr);
-
-/*
- * Return the SHA-1 of the nth object within the specified packfile.
- * Open the index if it is not already open.  The return value points
- * at the SHA-1 within the mmapped index.  Return NULL if there is an
- * error.
- */
-extern const unsigned char *nth_packed_object_sha1(struct packed_git *, uint32_t n);
-/*
- * Like nth_packed_object_sha1, but write the data into the object specified by
- * the the first argument.  Returns the first argument on success, and NULL on
- * error.
- */
-extern const struct object_id *nth_packed_object_oid(struct object_id *, struct packed_git *, uint32_t n);
-
-/*
- * Return the offset of the nth object within the specified packfile.
- * The index must already be opened.
- */
-extern off_t nth_packed_object_offset(const struct packed_git *, uint32_t n);
-
-/*
- * If the object named sha1 is present in the specified packfile,
- * return its offset within the packfile; otherwise, return 0.
- */
-extern off_t find_pack_entry_one(const unsigned char *sha1, struct packed_git *);
-
-extern int is_pack_valid(struct packed_git *);
-extern void *unpack_entry(struct packed_git *, off_t, enum object_type *, unsigned long *);
-extern unsigned long unpack_object_header_buffer(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep);
-extern unsigned long get_size_from_delta(struct packed_git *, struct pack_window **, off_t);
-extern int unpack_object_header(struct packed_git *, struct pack_window **, off_t *, unsigned long *);
-
-/*
  * Iterate over the files in the loose-object parts of the object
  * directory "path", triggering the following callbacks:
  *
@@ -1776,17 +1662,12 @@ int for_each_loose_file_in_objdir_buf(struct strbuf *path,
 				      void *data);
 
 /*
- * Iterate over loose and packed objects in both the local
+ * Iterate over loose objects in both the local
  * repository and any alternates repositories (unless the
  * LOCAL_ONLY flag is set).
  */
 #define FOR_EACH_OBJECT_LOCAL_ONLY 0x1
-typedef int each_packed_object_fn(const struct object_id *oid,
-				  struct packed_git *pack,
-				  uint32_t pos,
-				  void *data);
 extern int for_each_loose_object(each_loose_object_fn, void *, unsigned flags);
-extern int for_each_packed_object(each_packed_object_fn, void *, unsigned flags);
 
 struct object_info {
 	/* Request */
@@ -1836,7 +1717,6 @@ struct object_info {
 /* Do not retry packed storage after checking packed and loose storage */
 #define OBJECT_INFO_QUICK 8
 extern int sha1_object_info_extended(const unsigned char *, struct object_info *, unsigned flags);
-extern int packed_object_info(struct packed_git *pack, off_t offset, struct object_info *);
 
 /* Dumb servers support */
 extern int update_server_info(int);
diff --git a/connected.c b/connected.c
index 136c2ac168..f416b05051 100644
--- a/connected.c
+++ b/connected.c
@@ -3,6 +3,7 @@
 #include "sigchain.h"
 #include "connected.h"
 #include "transport.h"
+#include "packfile.h"
 
 /*
  * If we feed all the commits we want to verify to this command
diff --git a/diff.c b/diff.c
index a74cc08488..3d3e553a98 100644
--- a/diff.c
+++ b/diff.c
@@ -21,6 +21,7 @@
 #include "string-list.h"
 #include "argv-array.h"
 #include "graph.h"
+#include "packfile.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
 #define FAST_WORKING_DIRECTORY 0
diff --git a/fast-import.c b/fast-import.c
index a959161b46..49516d60e6 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -167,6 +167,7 @@ Format of STDIN stream:
 #include "quote.h"
 #include "dir.h"
 #include "run-command.h"
+#include "packfile.h"
 
 #define PACK_ID_BITS 16
 #define MAX_PACK_ID ((1<<PACK_ID_BITS)-1)
diff --git a/fetch-pack.c b/fetch-pack.c
index fbbc99c888..105506e9aa 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -17,6 +17,7 @@
 #include "prio-queue.h"
 #include "sha1-array.h"
 #include "oidset.h"
+#include "packfile.h"
 
 static int transfer_unpack_limit = -1;
 static int fetch_unpack_limit = -1;
diff --git a/git-compat-util.h b/git-compat-util.h
index 7d2c0ca759..6678b488cc 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -749,8 +749,6 @@ const char *inet_ntop(int af, const void *src, char *dst, size_t size);
 extern int git_atexit(void (*handler)(void));
 #endif
 
-extern void release_pack_memory(size_t);
-
 typedef void (*try_to_free_t)(size_t);
 extern try_to_free_t set_try_to_free_routine(try_to_free_t);
 
diff --git a/http-backend.c b/http-backend.c
index 519025d2c3..8076b1d5e5 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -9,6 +9,7 @@
 #include "string-list.h"
 #include "url.h"
 #include "argv-array.h"
+#include "packfile.h"
 
 static const char content_type[] = "Content-Type";
 static const char content_length[] = "Content-Length";
diff --git a/http-push.c b/http-push.c
index c91f40a610..e4c9b065ce 100644
--- a/http-push.c
+++ b/http-push.c
@@ -11,6 +11,7 @@
 #include "list-objects.h"
 #include "sigchain.h"
 #include "argv-array.h"
+#include "packfile.h"
 
 #ifdef EXPAT_NEEDS_XMLPARSE_H
 #include <xmlparse.h>
diff --git a/http-walker.c b/http-walker.c
index ee049cb13d..1ae8363de2 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -4,6 +4,7 @@
 #include "http.h"
 #include "list.h"
 #include "transport.h"
+#include "packfile.h"
 
 struct alt_base {
 	char *base;
diff --git a/http.c b/http.c
index fa8666a21f..9e40a465fd 100644
--- a/http.c
+++ b/http.c
@@ -11,6 +11,7 @@
 #include "pkt-line.h"
 #include "gettext.h"
 #include "transport.h"
+#include "packfile.h"
 
 static struct trace_key trace_curl = TRACE_KEY_INIT(CURL);
 #if LIBCURL_VERSION_NUM >= 0x070a08
diff --git a/outgoing/packfile.h b/outgoing/packfile.h
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/outgoing/packfile.h
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 327634cd71..cb3d14ba45 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -9,6 +9,7 @@
 #include "pack-bitmap.h"
 #include "pack-revindex.h"
 #include "pack-objects.h"
+#include "packfile.h"
 
 /*
  * An entry on the bitmap index, representing the bitmap for a given
diff --git a/pack-check.c b/pack-check.c
index e1fcb228fa..073c1fbd46 100644
--- a/pack-check.c
+++ b/pack-check.c
@@ -2,6 +2,7 @@
 #include "pack.h"
 #include "pack-revindex.h"
 #include "progress.h"
+#include "packfile.h"
 
 struct idx_entry {
 	off_t                offset;
diff --git a/packfile.c b/packfile.c
new file mode 100644
index 0000000000..f86fa051c9
--- /dev/null
+++ b/packfile.c
@@ -0,0 +1,1896 @@
+#include "cache.h"
+#include "mru.h"
+#include "pack.h"
+#include "dir.h"
+#include "mergesort.h"
+#include "packfile.h"
+#include "delta.h"
+#include "list.h"
+#include "streaming.h"
+#include "sha1-lookup.h"
+
+char *odb_pack_name(struct strbuf *buf,
+		    const unsigned char *sha1,
+		    const char *ext)
+{
+	strbuf_reset(buf);
+	strbuf_addf(buf, "%s/pack/pack-%s.%s", get_object_directory(),
+		    sha1_to_hex(sha1), ext);
+	return buf->buf;
+}
+
+char *sha1_pack_name(const unsigned char *sha1)
+{
+	static struct strbuf buf = STRBUF_INIT;
+	return odb_pack_name(&buf, sha1, "pack");
+}
+
+char *sha1_pack_index_name(const unsigned char *sha1)
+{
+	static struct strbuf buf = STRBUF_INIT;
+	return odb_pack_name(&buf, sha1, "idx");
+}
+
+static unsigned int pack_used_ctr;
+static unsigned int pack_mmap_calls;
+static unsigned int peak_pack_open_windows;
+static unsigned int pack_open_windows;
+static unsigned int pack_open_fds;
+static unsigned int pack_max_fds;
+static size_t peak_pack_mapped;
+static size_t pack_mapped;
+struct packed_git *packed_git;
+
+static struct mru packed_git_mru_storage;
+struct mru *packed_git_mru = &packed_git_mru_storage;
+
+#define SZ_FMT PRIuMAX
+static inline uintmax_t sz_fmt(size_t s) { return s; }
+
+void pack_report(void)
+{
+	fprintf(stderr,
+		"pack_report: getpagesize()            = %10" SZ_FMT "\n"
+		"pack_report: core.packedGitWindowSize = %10" SZ_FMT "\n"
+		"pack_report: core.packedGitLimit      = %10" SZ_FMT "\n",
+		sz_fmt(getpagesize()),
+		sz_fmt(packed_git_window_size),
+		sz_fmt(packed_git_limit));
+	fprintf(stderr,
+		"pack_report: pack_used_ctr            = %10u\n"
+		"pack_report: pack_mmap_calls          = %10u\n"
+		"pack_report: pack_open_windows        = %10u / %10u\n"
+		"pack_report: pack_mapped              = "
+			"%10" SZ_FMT " / %10" SZ_FMT "\n",
+		pack_used_ctr,
+		pack_mmap_calls,
+		pack_open_windows, peak_pack_open_windows,
+		sz_fmt(pack_mapped), sz_fmt(peak_pack_mapped));
+}
+
+/*
+ * Open and mmap the index file at path, perform a couple of
+ * consistency checks, then record its information to p.  Return 0 on
+ * success.
+ */
+static int check_packed_git_idx(const char *path, struct packed_git *p)
+{
+	void *idx_map;
+	struct pack_idx_header *hdr;
+	size_t idx_size;
+	uint32_t version, nr, i, *index;
+	int fd = git_open(path);
+	struct stat st;
+
+	if (fd < 0)
+		return -1;
+	if (fstat(fd, &st)) {
+		close(fd);
+		return -1;
+	}
+	idx_size = xsize_t(st.st_size);
+	if (idx_size < 4 * 256 + 20 + 20) {
+		close(fd);
+		return error("index file %s is too small", path);
+	}
+	idx_map = xmmap(NULL, idx_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	close(fd);
+
+	hdr = idx_map;
+	if (hdr->idx_signature == htonl(PACK_IDX_SIGNATURE)) {
+		version = ntohl(hdr->idx_version);
+		if (version < 2 || version > 2) {
+			munmap(idx_map, idx_size);
+			return error("index file %s is version %"PRIu32
+				     " and is not supported by this binary"
+				     " (try upgrading GIT to a newer version)",
+				     path, version);
+		}
+	} else
+		version = 1;
+
+	nr = 0;
+	index = idx_map;
+	if (version > 1)
+		index += 2;  /* skip index header */
+	for (i = 0; i < 256; i++) {
+		uint32_t n = ntohl(index[i]);
+		if (n < nr) {
+			munmap(idx_map, idx_size);
+			return error("non-monotonic index %s", path);
+		}
+		nr = n;
+	}
+
+	if (version == 1) {
+		/*
+		 * Total size:
+		 *  - 256 index entries 4 bytes each
+		 *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
+		 *  - 20-byte SHA1 of the packfile
+		 *  - 20-byte SHA1 file checksum
+		 */
+		if (idx_size != 4*256 + nr * 24 + 20 + 20) {
+			munmap(idx_map, idx_size);
+			return error("wrong index v1 file size in %s", path);
+		}
+	} else if (version == 2) {
+		/*
+		 * Minimum size:
+		 *  - 8 bytes of header
+		 *  - 256 index entries 4 bytes each
+		 *  - 20-byte sha1 entry * nr
+		 *  - 4-byte crc entry * nr
+		 *  - 4-byte offset entry * nr
+		 *  - 20-byte SHA1 of the packfile
+		 *  - 20-byte SHA1 file checksum
+		 * And after the 4-byte offset table might be a
+		 * variable sized table containing 8-byte entries
+		 * for offsets larger than 2^31.
+		 */
+		unsigned long min_size = 8 + 4*256 + nr*(20 + 4 + 4) + 20 + 20;
+		unsigned long max_size = min_size;
+		if (nr)
+			max_size += (nr - 1)*8;
+		if (idx_size < min_size || idx_size > max_size) {
+			munmap(idx_map, idx_size);
+			return error("wrong index v2 file size in %s", path);
+		}
+		if (idx_size != min_size &&
+		    /*
+		     * make sure we can deal with large pack offsets.
+		     * 31-bit signed offset won't be enough, neither
+		     * 32-bit unsigned one will be.
+		     */
+		    (sizeof(off_t) <= 4)) {
+			munmap(idx_map, idx_size);
+			return error("pack too large for current definition of off_t in %s", path);
+		}
+	}
+
+	p->index_version = version;
+	p->index_data = idx_map;
+	p->index_size = idx_size;
+	p->num_objects = nr;
+	return 0;
+}
+
+int open_pack_index(struct packed_git *p)
+{
+	char *idx_name;
+	size_t len;
+	int ret;
+
+	if (p->index_data)
+		return 0;
+
+	if (!strip_suffix(p->pack_name, ".pack", &len))
+		die("BUG: pack_name does not end in .pack");
+	idx_name = xstrfmt("%.*s.idx", (int)len, p->pack_name);
+	ret = check_packed_git_idx(idx_name, p);
+	free(idx_name);
+	return ret;
+}
+
+static struct packed_git *alloc_packed_git(int extra)
+{
+	struct packed_git *p = xmalloc(st_add(sizeof(*p), extra));
+	memset(p, 0, sizeof(*p));
+	p->pack_fd = -1;
+	return p;
+}
+
+struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path)
+{
+	const char *path = sha1_pack_name(sha1);
+	size_t alloc = st_add(strlen(path), 1);
+	struct packed_git *p = alloc_packed_git(alloc);
+
+	memcpy(p->pack_name, path, alloc); /* includes NUL */
+	hashcpy(p->sha1, sha1);
+	if (check_packed_git_idx(idx_path, p)) {
+		free(p);
+		return NULL;
+	}
+
+	return p;
+}
+
+static void scan_windows(struct packed_git *p,
+	struct packed_git **lru_p,
+	struct pack_window **lru_w,
+	struct pack_window **lru_l)
+{
+	struct pack_window *w, *w_l;
+
+	for (w_l = NULL, w = p->windows; w; w = w->next) {
+		if (!w->inuse_cnt) {
+			if (!*lru_w || w->last_used < (*lru_w)->last_used) {
+				*lru_p = p;
+				*lru_w = w;
+				*lru_l = w_l;
+			}
+		}
+		w_l = w;
+	}
+}
+
+static int unuse_one_window(struct packed_git *current)
+{
+	struct packed_git *p, *lru_p = NULL;
+	struct pack_window *lru_w = NULL, *lru_l = NULL;
+
+	if (current)
+		scan_windows(current, &am