read-cache.c - jrn/git - Git at Google

 /*
  * GIT - The information manager from hell
  *
  * Copyright (C) Linus Torvalds, 2005
  */
 #include "cache.h"

 const char *sha1_file_directory = NULL;
 struct cache_entry **active_cache = NULL;
 unsigned int active_nr = 0, active_alloc = 0;

 void usage(const char *err, ...)
 {
 	va_list args;
 	char string[200];

 	va_start(args, err);
 	vsnprintf(string, sizeof(string), err, args);
 	va_end(args);
 	fprintf(stderr, "%s\n", string);
 	exit(1);
 }

 static unsigned hexval(char c)
 {
 	if (c >= '0' && c <= '9')
 		return c - '0';
 	if (c >= 'a' && c <= 'f')
 		return c - 'a' + 10;
 	if (c >= 'A' && c <= 'F')
 		return c - 'A' + 10;
 	return ~0;
 }

 int get_sha1_hex(const char *hex, unsigned char *sha1)
 {
 	int i;
 	for (i = 0; i < 20; i++) {
 		unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
 		if (val & ~0xff)
 			return -1;
 		*sha1++ = val;
 		hex += 2;
 	}
 	return 0;
 }

 char * sha1_to_hex(const unsigned char *sha1)
 {
 	static char buffer[50];
 	static const char hex[] = "0123456789abcdef";
 	char *buf = buffer;
 	int i;

 	for (i = 0; i < 20; i++) {
 		unsigned int val = *sha1++;
 		*buf++ = hex[val >> 4];
 		*buf++ = hex[val & 0xf];
 	}
 	return buffer;
 }

 /*
  * NOTE! This returns a statically allocated buffer, so you have to be
  * careful about using it. Do a "strdup()" if you need to save the
  * filename.
  */
 char *sha1_file_name(const unsigned char *sha1)
 {
 	int i;
 	static char *name, *base;

 	if (!base) {
 		char *sha1_file_directory = getenv(DB_ENVIRONMENT) ? : DEFAULT_DB_ENVIRONMENT;
 		int len = strlen(sha1_file_directory);
 		base = malloc(len + 60);
 		memcpy(base, sha1_file_directory, len);
 		memset(base+len, 0, 60);
 		base[len] = '/';
 		base[len+3] = '/';
 		name = base + len + 1;
 	}
 	for (i = 0; i < 20; i++) {
 		static char hex[] = "0123456789abcdef";
 		unsigned int val = sha1[i];
 		char *pos = name + i*2 + (i > 0);
 		*pos++ = hex[val >> 4];
 		*pos = hex[val & 0xf];
 	}
 	return base;
 }

 int check_sha1_signature(unsigned char *sha1, void *map, unsigned long size)
 {
 	unsigned char real_sha1[20];
 	SHA_CTX c;

 	SHA1_Init(&c);
 	SHA1_Update(&c, map, size);
 	SHA1_Final(real_sha1, &c);
 	return memcmp(sha1, real_sha1, 20) ? -1 : 0;
 }

 void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 {
 	char *filename = sha1_file_name(sha1);
 	int fd = open(filename, O_RDONLY);
 	struct stat st;
 	void *map;

 	if (fd < 0) {
 		perror(filename);
 		return NULL;
 	}
 	if (fstat(fd, &st) < 0) {
 		close(fd);
 		return NULL;
 	}
 	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
 	if (-1 == (int)(long)map)
 		return NULL;
 	*size = st.st_size;
 	return map;
 }

 void * unpack_sha1_file(void *map, unsigned long mapsize, char *type, unsigned long *size)
 {
 	int ret, bytes;
 	z_stream stream;
 	char buffer[8192];
 	char *buf;

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

 	inflateInit(&stream);
 	ret = inflate(&stream, 0);
 	if (sscanf(buffer, "%10s %lu", type, size) != 2)
 		return NULL;

 	bytes = strlen(buffer) + 1;
 	buf = malloc(*size);
 	if (!buf)
 		return NULL;

 	memcpy(buf, buffer + bytes, stream.total_out - bytes);
 	bytes = stream.total_out - bytes;
 	if (bytes < *size && ret == Z_OK) {
 		stream.next_out = buf + bytes;
 		stream.avail_out = *size - bytes;
 		while (inflate(&stream, Z_FINISH) == Z_OK)
 			/* nothing */;
 	}
 	inflateEnd(&stream);
 	return buf;
 }

 void * read_sha1_file(const unsigned char *sha1, char *type, unsigned long *size)
 {
 	unsigned long mapsize;
 	void *map, *buf;

 	map = map_sha1_file(sha1, &mapsize);
 	if (map) {
 		buf = unpack_sha1_file(map, mapsize, type, size);
 		munmap(map, mapsize);
 		return buf;
 	}
 	return NULL;
 }

 int write_sha1_file(char *buf, unsigned len, unsigned char *returnsha1)
 {
 	int size;
 	char *compressed;
 	z_stream stream;
 	unsigned char sha1[20];
 	SHA_CTX c;

 	/* Set it up */
 	memset(&stream, 0, sizeof(stream));
 	deflateInit(&stream, Z_BEST_COMPRESSION);
 	size = deflateBound(&stream, len);
 	compressed = malloc(size);

 	/* Compress it */
 	stream.next_in = buf;
 	stream.avail_in = len;
 	stream.next_out = compressed;
 	stream.avail_out = size;
 	while (deflate(&stream, Z_FINISH) == Z_OK)
 		/* nothing */;
 	deflateEnd(&stream);
 	size = stream.total_out;

 	/* Sha1.. */
 	SHA1_Init(&c);
 	SHA1_Update(&c, compressed, size);
 	SHA1_Final(sha1, &c);

 	if (write_sha1_buffer(sha1, compressed, size) < 0)
 		return -1;
 	if (returnsha1)
 		memcpy(returnsha1, sha1, 20);
 	return 0;
 }

 int write_sha1_buffer(const unsigned char *sha1, void *buf, unsigned int size)
 {
 	char *filename = sha1_file_name(sha1);
 	int fd;

 	fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0666);
 	if (fd < 0)
 		return (errno == EEXIST) ? 0 : -1;
 	write(fd, buf, size);
 	close(fd);
 	return 0;
 }

 static int error(const char * string)
 {
 	fprintf(stderr, "error: %s\n", string);
 	return -1;
 }

 int cache_match_stat(struct cache_entry *ce, struct stat *st)
 {
 	unsigned int changed = 0;

 	if (ce->mtime.sec  != (unsigned int)st->st_mtim.tv_sec ||
 	    ce->mtime.nsec != (unsigned int)st->st_mtim.tv_nsec)
 		changed |= MTIME_CHANGED;
 	if (ce->ctime.sec  != (unsigned int)st->st_ctim.tv_sec ||
 	    ce->ctime.nsec != (unsigned int)st->st_ctim.tv_nsec)
 		changed |= CTIME_CHANGED;
 	if (ce->st_uid != (unsigned int)st->st_uid ||
 	    ce->st_gid != (unsigned int)st->st_gid)
 		changed |= OWNER_CHANGED;
 	if (ce->st_mode != (unsigned int)st->st_mode)
 		changed |= MODE_CHANGED;
 	if (ce->st_dev != (unsigned int)st->st_dev ||
 	    ce->st_ino != (unsigned int)st->st_ino)
 		changed |= INODE_CHANGED;
 	if (ce->st_size != (unsigned int)st->st_size)
 		changed |= DATA_CHANGED;
 	return changed;
 }

 int cache_name_compare(const char *name1, int len1, const char *name2, int len2)
 {
 	int len = len1 < len2 ? len1 : len2;
 	int cmp;

 	cmp = memcmp(name1, name2, len);
 	if (cmp)
 		return cmp;
 	if (len1 < len2)
 		return -1;
 	if (len1 > len2)
 		return 1;
 	return 0;
 }

 int cache_name_pos(const char *name, int namelen)
 {
 	int first, last;

 	first = 0;
 	last = active_nr;
 	while (last > first) {
 		int next = (last + first) >> 1;
 		struct cache_entry *ce = active_cache[next];
 		int cmp = cache_name_compare(name, namelen, ce->name, ce->namelen);
 		if (!cmp)
 			return next;
 		if (cmp < 0) {
 			last = next;
 			continue;
 		}
 		first = next+1;
 	}
 	return -first-1;
 }

 int remove_file_from_cache(char *path)
 {
 	int pos = cache_name_pos(path, strlen(path));
 	if (pos >= 0) {
 		active_nr--;
 		if (pos < active_nr)
 			memmove(active_cache + pos, active_cache + pos + 1, (active_nr - pos) * sizeof(struct cache_entry *));
 	}
 	return 0;
 }

 int add_cache_entry(struct cache_entry *ce, int ok_to_add)
 {
 	int pos;

 	pos = cache_name_pos(ce->name, ce->namelen);

 	/* existing match? Just replace it */
 	if (pos >= 0) {
 		active_cache[pos] = ce;
 		return 0;
 	}
 	pos = -pos-1;

 	if (!ok_to_add)
 		return -1;

 	/* Make sure the array is big enough .. */
 	if (active_nr == active_alloc) {
 		active_alloc = alloc_nr(active_alloc);
 		active_cache = realloc(active_cache, active_alloc * sizeof(struct cache_entry *));
 	}

 	/* Add it in.. */
 	active_nr++;
 	if (active_nr > pos)
 		memmove(active_cache + pos + 1, active_cache + pos, (active_nr - pos - 1) * sizeof(ce));
 	active_cache[pos] = ce;
 	return 0;
 }

 static int verify_hdr(struct cache_header *hdr, unsigned long size)
 {
 	SHA_CTX c;
 	unsigned char sha1[20];

 	if (hdr->signature != CACHE_SIGNATURE)
 		return error("bad signature");
 	if (hdr->version != 1)
 		return error("bad version");
 	SHA1_Init(&c);
 	SHA1_Update(&c, hdr, offsetof(struct cache_header, sha1));
 	SHA1_Update(&c, hdr+1, size - sizeof(*hdr));
 	SHA1_Final(sha1, &c);
 	if (memcmp(sha1, hdr->sha1, 20))
 		return error("bad header sha1");
 	return 0;
 }

 int read_cache(void)
 {
 	int fd, i;
 	struct stat st;
 	unsigned long size, offset;
 	void *map;
 	struct cache_header *hdr;

 	errno = EBUSY;
 	if (active_cache)
 		return error("more than one cachefile");
 	errno = ENOENT;
 	sha1_file_directory = getenv(DB_ENVIRONMENT);
 	if (!sha1_file_directory)
 		sha1_file_directory = DEFAULT_DB_ENVIRONMENT;
 	if (access(sha1_file_directory, X_OK) < 0)
 		return error("no access to SHA1 file directory");
 	fd = open(".git/index", O_RDONLY);
 	if (fd < 0)
 		return (errno == ENOENT) ? 0 : error("open failed");

 	size = 0; // avoid gcc warning
 	map = (void *)-1;
 	if (!fstat(fd, &st)) {
 		size = st.st_size;
 		errno = EINVAL;
 		if (size >= sizeof(struct cache_header))
 			map = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
 	}
 	close(fd);
 	if (-1 == (int)(long)map)
 		return error("mmap failed");

 	hdr = map;
 	if (verify_hdr(hdr, size) < 0)
 		goto unmap;

 	active_nr = hdr->entries;
 	active_alloc = alloc_nr(active_nr);
 	active_cache = calloc(active_alloc, sizeof(struct cache_entry *));

 	offset = sizeof(*hdr);
 	for (i = 0; i < hdr->entries; i++) {
 		struct cache_entry *ce = map + offset;
 		offset = offset + ce_size(ce);
 		active_cache[i] = ce;
 	}
 	return active_nr;

 unmap:
 	munmap(map, size);
 	errno = EINVAL;
 	return error("verify header failed");
 }

 int write_cache(int newfd, struct cache_entry **cache, int entries)
 {
 	SHA_CTX c;
 	struct cache_header hdr;
 	int i;

 	hdr.signature = CACHE_SIGNATURE;
 	hdr.version = 1;
 	hdr.entries = entries;

 	SHA1_Init(&c);
 	SHA1_Update(&c, &hdr, offsetof(struct cache_header, sha1));
 	for (i = 0; i < entries; i++) {
 		struct cache_entry *ce = cache[i];
 		int size = ce_size(ce);
 		SHA1_Update(&c, ce, size);
 	}
 	SHA1_Final(hdr.sha1, &c);

 	if (write(newfd, &hdr, sizeof(hdr)) != sizeof(hdr))
 		return -1;

 	for (i = 0; i < entries; i++) {
 		struct cache_entry *ce = cache[i];
 		int size = ce_size(ce);
 		if (write(newfd, ce, size) != size)
 			return -1;
 	}
 	return 0;
 }
	/*
	* GIT - The information manager from hell
	*
	* Copyright (C) Linus Torvalds, 2005
	*/
	#include "cache.h"

	const char *sha1_file_directory = NULL;
	struct cache_entry **active_cache = NULL;
	unsigned int active_nr = 0, active_alloc = 0;

	void usage(const char *err, ...)
	{
	va_list args;
	char string[200];

	va_start(args, err);
	vsnprintf(string, sizeof(string), err, args);
	va_end(args);
	fprintf(stderr, "%s\n", string);
	exit(1);
	}

	static unsigned hexval(char c)
	{
	if (c >= '0' && c <= '9')
	return c - '0';
	if (c >= 'a' && c <= 'f')
	return c - 'a' + 10;
	if (c >= 'A' && c <= 'F')
	return c - 'A' + 10;
	return ~0;
	}

	int get_sha1_hex(const char hex, unsigned char sha1)
	{
	int i;
	for (i = 0; i < 20; i++) {
	unsigned int val = (hexval(hex[0]) << 4) \| hexval(hex[1]);
	if (val & ~0xff)
	return -1;
	*sha1++ = val;
	hex += 2;
	}
	return 0;
	}

	char * sha1_to_hex(const unsigned char *sha1)
	{
	static char buffer[50];
	static const char hex[] = "0123456789abcdef";
	char *buf = buffer;
	int i;

	for (i = 0; i < 20; i++) {
	unsigned int val = *sha1++;
	*buf++ = hex[val >> 4];
	*buf++ = hex[val & 0xf];
	}
	return buffer;
	}

	/*
	* NOTE! This returns a statically allocated buffer, so you have to be
	* careful about using it. Do a "strdup()" if you need to save the
	* filename.
	*/
	char sha1_file_name(const unsigned char sha1)
	{
	int i;
	static char name, base;

	if (!base) {
	char *sha1_file_directory = getenv(DB_ENVIRONMENT) ? : DEFAULT_DB_ENVIRONMENT;
	int len = strlen(sha1_file_directory);
	base = malloc(len + 60);
	memcpy(base, sha1_file_directory, len);
	memset(base+len, 0, 60);
	base[len] = '/';
	base[len+3] = '/';
	name = base + len + 1;
	}
	for (i = 0; i < 20; i++) {
	static char hex[] = "0123456789abcdef";
	unsigned int val = sha1[i];
	char pos = name + i2 + (i > 0);
	*pos++ = hex[val >> 4];
	*pos = hex[val & 0xf];
	}
	return base;
	}

	int check_sha1_signature(unsigned char sha1, void map, unsigned long size)
	{
	unsigned char real_sha1[20];
	SHA_CTX c;

	SHA1_Init(&c);
	SHA1_Update(&c, map, size);
	SHA1_Final(real_sha1, &c);
	return memcmp(sha1, real_sha1, 20) ? -1 : 0;
	}

	void map_sha1_file(const unsigned char sha1, unsigned long *size)
	{
	char *filename = sha1_file_name(sha1);
	int fd = open(filename, O_RDONLY);
	struct stat st;
	void *map;

	if (fd < 0) {
	perror(filename);
	return NULL;
	}
	if (fstat(fd, &st) < 0) {
	close(fd);
	return NULL;
	}
	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
	close(fd);
	if (-1 == (int)(long)map)
	return NULL;
	*size = st.st_size;
	return map;
	}

	void * unpack_sha1_file(void map, unsigned long mapsize, char type, unsigned long *size)
	{
	int ret, bytes;
	z_stream stream;
	char buffer[8192];
	char *buf;

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

	inflateInit(&stream);
	ret = inflate(&stream, 0);
	if (sscanf(buffer, "%10s %lu", type, size) != 2)
	return NULL;

	bytes = strlen(buffer) + 1;
	buf = malloc(*size);
	if (!buf)
	return NULL;

	memcpy(buf, buffer + bytes, stream.total_out - bytes);
	bytes = stream.total_out - bytes;
	if (bytes < *size && ret == Z_OK) {
	stream.next_out = buf + bytes;
	stream.avail_out = *size - bytes;
	while (inflate(&stream, Z_FINISH) == Z_OK)
	/* nothing */;
	}
	inflateEnd(&stream);
	return buf;
	}

	void * read_sha1_file(const unsigned char sha1, char type, unsigned long *size)
	{
	unsigned long mapsize;
	void map, buf;

	map = map_sha1_file(sha1, &mapsize);
	if (map) {
	buf = unpack_sha1_file(map, mapsize, type, size);
	munmap(map, mapsize);
	return buf;
	}
	return NULL;
	}

	int write_sha1_file(char buf, unsigned len, unsigned char returnsha1)
	{
	int size;
	char *compressed;
	z_stream stream;
	unsigned char sha1[20];
	SHA_CTX c;

	/* Set it up */
	memset(&stream, 0, sizeof(stream));
	deflateInit(&stream, Z_BEST_COMPRESSION);
	size = deflateBound(&stream, len);
	compressed = malloc(size);

	/* Compress it */
	stream.next_in = buf;
	stream.avail_in = len;
	stream.next_out = compressed;
	stream.avail_out = size;
	while (deflate(&stream, Z_FINISH) == Z_OK)
	/* nothing */;
	deflateEnd(&stream);
	size = stream.total_out;

	/* Sha1.. */
	SHA1_Init(&c);
	SHA1_Update(&c, compressed, size);
	SHA1_Final(sha1, &c);

	if (write_sha1_buffer(sha1, compressed, size) < 0)
	return -1;
	if (returnsha1)
	memcpy(returnsha1, sha1, 20);
	return 0;
	}

	int write_sha1_buffer(const unsigned char sha1, void buf, unsigned int size)
	{
	char *filename = sha1_file_name(sha1);
	int fd;

	fd = open(filename, O_WRONLY \| O_CREAT \| O_EXCL, 0666);
	if (fd < 0)
	return (errno == EEXIST) ? 0 : -1;
	write(fd, buf, size);
	close(fd);
	return 0;
	}

	static int error(const char * string)
	{
	fprintf(stderr, "error: %s\n", string);
	return -1;
	}

	int cache_match_stat(struct cache_entry ce, struct stat st)
	{
	unsigned int changed = 0;

	if (ce->mtime.sec != (unsigned int)st->st_mtim.tv_sec \|\|
	ce->mtime.nsec != (unsigned int)st->st_mtim.tv_nsec)
	changed \|= MTIME_CHANGED;
	if (ce->ctime.sec != (unsigned int)st->st_ctim.tv_sec \|\|
	ce->ctime.nsec != (unsigned int)st->st_ctim.tv_nsec)
	changed \|= CTIME_CHANGED;
	if (ce->st_uid != (unsigned int)st->st_uid \|\|
	ce->st_gid != (unsigned int)st->st_gid)
	changed \|= OWNER_CHANGED;
	if (ce->st_mode != (unsigned int)st->st_mode)
	changed \|= MODE_CHANGED;
	if (ce->st_dev != (unsigned int)st->st_dev \|\|
	ce->st_ino != (unsigned int)st->st_ino)
	changed \|= INODE_CHANGED;
	if (ce->st_size != (unsigned int)st->st_size)
	changed \|= DATA_CHANGED;
	return changed;
	}

	int cache_name_compare(const char name1, int len1, const char name2, int len2)
	{
	int len = len1 < len2 ? len1 : len2;
	int cmp;

	cmp = memcmp(name1, name2, len);
	if (cmp)
	return cmp;
	if (len1 < len2)
	return -1;
	if (len1 > len2)
	return 1;
	return 0;
	}

	int cache_name_pos(const char *name, int namelen)
	{
	int first, last;

	first = 0;
	last = active_nr;
	while (last > first) {
	int next = (last + first) >> 1;
	struct cache_entry *ce = active_cache[next];
	int cmp = cache_name_compare(name, namelen, ce->name, ce->namelen);
	if (!cmp)
	return next;
	if (cmp < 0) {
	last = next;
	continue;
	}
	first = next+1;
	}
	return -first-1;
	}

	int remove_file_from_cache(char *path)
	{
	int pos = cache_name_pos(path, strlen(path));
	if (pos >= 0) {
	active_nr--;
	if (pos < active_nr)
	memmove(active_cache + pos, active_cache + pos + 1, (active_nr - pos) * sizeof(struct cache_entry *));
	}
	return 0;
	}

	int add_cache_entry(struct cache_entry *ce, int ok_to_add)
	{
	int pos;

	pos = cache_name_pos(ce->name, ce->namelen);

	/* existing match? Just replace it */
	if (pos >= 0) {
	active_cache[pos] = ce;
	return 0;
	}
	pos = -pos-1;

	if (!ok_to_add)
	return -1;

	/* Make sure the array is big enough .. */
	if (active_nr == active_alloc) {
	active_alloc = alloc_nr(active_alloc);
	active_cache = realloc(active_cache, active_alloc * sizeof(struct cache_entry *));
	}

	/* Add it in.. */
	active_nr++;
	if (active_nr > pos)
	memmove(active_cache + pos + 1, active_cache + pos, (active_nr - pos - 1) * sizeof(ce));
	active_cache[pos] = ce;
	return 0;
	}

	static int verify_hdr(struct cache_header *hdr, unsigned long size)
	{
	SHA_CTX c;
	unsigned char sha1[20];

	if (hdr->signature != CACHE_SIGNATURE)
	return error("bad signature");
	if (hdr->version != 1)
	return error("bad version");
	SHA1_Init(&c);
	SHA1_Update(&c, hdr, offsetof(struct cache_header, sha1));
	SHA1_Update(&c, hdr+1, size - sizeof(*hdr));
	SHA1_Final(sha1, &c);
	if (memcmp(sha1, hdr->sha1, 20))
	return error("bad header sha1");
	return 0;
	}

	int read_cache(void)
	{
	int fd, i;
	struct stat st;
	unsigned long size, offset;
	void *map;
	struct cache_header *hdr;

	errno = EBUSY;
	if (active_cache)
	return error("more than one cachefile");
	errno = ENOENT;
	sha1_file_directory = getenv(DB_ENVIRONMENT);
	if (!sha1_file_directory)
	sha1_file_directory = DEFAULT_DB_ENVIRONMENT;
	if (access(sha1_file_directory, X_OK) < 0)
	return error("no access to SHA1 file directory");
	fd = open(".git/index", O_RDONLY);
	if (fd < 0)
	return (errno == ENOENT) ? 0 : error("open failed");

	size = 0; // avoid gcc warning
	map = (void *)-1;
	if (!fstat(fd, &st)) {
	size = st.st_size;
	errno = EINVAL;
	if (size >= sizeof(struct cache_header))
	map = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
	}
	close(fd);
	if (-1 == (int)(long)map)
	return error("mmap failed");

	hdr = map;
	if (verify_hdr(hdr, size) < 0)
	goto unmap;

	active_nr = hdr->entries;
	active_alloc = alloc_nr(active_nr);
	active_cache = calloc(active_alloc, sizeof(struct cache_entry *));

	offset = sizeof(*hdr);
	for (i = 0; i < hdr->entries; i++) {
	struct cache_entry *ce = map + offset;
	offset = offset + ce_size(ce);
	active_cache[i] = ce;
	}
	return active_nr;

	unmap:
	munmap(map, size);
	errno = EINVAL;
	return error("verify header failed");
	}

	int write_cache(int newfd, struct cache_entry **cache, int entries)
	{
	SHA_CTX c;
	struct cache_header hdr;
	int i;

	hdr.signature = CACHE_SIGNATURE;
	hdr.version = 1;
	hdr.entries = entries;

	SHA1_Init(&c);
	SHA1_Update(&c, &hdr, offsetof(struct cache_header, sha1));
	for (i = 0; i < entries; i++) {
	struct cache_entry *ce = cache[i];
	int size = ce_size(ce);
	SHA1_Update(&c, ce, size);
	}
	SHA1_Final(hdr.sha1, &c);

	if (write(newfd, &hdr, sizeof(hdr)) != sizeof(hdr))
	return -1;

	for (i = 0; i < entries; i++) {
	struct cache_entry *ce = cache[i];
	int size = ce_size(ce);
	if (write(newfd, ce, size) != size)
	return -1;
	}
	return 0;
	}