Function PAG_replace_entry_first

src/jrd/pag.cpp:406–463

bool PAG_replace_entry_first(thread_db* tdbb, header_page* header,
							 USHORT type, USHORT len, const UCHAR* entry)
{
/***********************************************
 *
 *	P A G _ r e p l a c e _ e n t r y _ f i r s t
 *
 ***********************************************
 *
 * Functional description
 *	Replace an entry in the header page so it will become first entry
 *	This will be used mainly for the clumplets used for backup purposes
 *  because they are needed to be read without page lock
 *	Will not follow to hdr_next_page
 *	Will not journal changes made to page. => obsolete
 *	RETURNS
 *		true - modified page
 *		false - nothing done
 *
 **************************************/
	SET_TDBB(tdbb);
	Database* dbb = tdbb->getDatabase();
	CHECK_DBB(dbb);

	err_post_if_database_is_readonly(dbb);

	UCHAR* p = header->hdr_data;
	while (*p != HDR_end && *p != type) {
		p += 2u + p[1];
	}

	// Remove item if found it somewhere
	if (*p != HDR_end)
	{
		const USHORT shift = p[1] + 2u;
		memmove(p, p + shift, header->hdr_end - (p - (UCHAR*) header) - shift + 1); // to preserve HDR_end
		header->hdr_end -= shift;
	}

	if (!entry) {
		return false; // We were asked just to remove item. We finished.
	}

	// Check if we got enough space
	if (dbb->dbb_page_size - header->hdr_end <= len + 2) {
		BUGCHECK(251);
	}

	// Actually add the item
	fb_assert(len <= MAX_UCHAR);
	memmove(header->hdr_data + len + 2, header->hdr_data, header->hdr_end - HDR_SIZE + 1);
	header->hdr_data[0] = type;
	header->hdr_data[1] = len;
	memcpy(header->hdr_data + 2, entry, len);
	header->hdr_end += len + 2;

	return true;
}