Function do_read_index

read-cache.c:2198–2334

remember to discard_cache() before reading a different cache! */

/* remember to discard_cache() before reading a different cache! */
int do_read_index(struct index_state *istate, const char *path, int must_exist)
{
	int fd;
	struct stat st;
	unsigned long src_offset;
	const struct cache_header *hdr;
	const char *mmap;
	size_t mmap_size;
	struct load_index_extensions p;
	size_t extension_offset = 0;
	int nr_threads, cpus;
	struct index_entry_offset_table *ieot = NULL;

	if (istate->initialized)
		return istate->cache_nr;

	istate->timestamp.sec = 0;
	istate->timestamp.nsec = 0;
	fd = open(path, O_RDONLY);
	if (fd < 0) {
		if (!must_exist && errno == ENOENT) {
			set_new_index_sparsity(istate);
			istate->initialized = 1;
			return 0;
		}
		die_errno(_("%s: index file open failed"), path);
	}

	if (fstat(fd, &st))
		die_errno(_("%s: cannot stat the open index"), path);

	mmap_size = xsize_t(st.st_size);
	if (mmap_size < sizeof(struct cache_header) + the_hash_algo->rawsz)
		die(_("%s: index file smaller than expected"), path);

	mmap = xmmap_gently(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0);
	if (mmap == MAP_FAILED)
		die_errno(_("%s: unable to map index file%s"), path,
			mmap_os_err());
	close(fd);

	hdr = (const struct cache_header *)mmap;
	if (verify_hdr(hdr, mmap_size) < 0)
		goto unmap;

	oidread(&istate->oid, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz,
		the_repository->hash_algo);
	istate->version = ntohl(hdr->hdr_version);
	istate->cache_nr = ntohl(hdr->hdr_entries);
	istate->cache_alloc = alloc_nr(istate->cache_nr);
	CALLOC_ARRAY(istate->cache, istate->cache_alloc);
	istate->initialized = 1;

	p.istate = istate;
	p.mmap = mmap;
	p.mmap_size = mmap_size;

	src_offset = sizeof(*hdr);