The present invention relates to file control based on an electronic computer and more particularly, to a file control method based on unique file control information and file structure.
There is conventionally suggested such a method for storing files in an external memory in a computer system as provided by a UNIX (which is a registered trademark in U.S. and other countries exclusively licensed by the X/Open corporation) operating system. In the UNIX operating system, the external memory is controlled as divided into units called blocks to provide a means for recording data to be stored therein by computer's user into a file corresponding to a set of such blocks. In the UNIX operating system, the file is controlled based on control information known as i node. The i node stores therein a list of serial numbers of the blocks constituting the file. The i node is stored in the external memory while the computer's user does not use the file, whereas, when the user actually starts using the file to refer to or update the file, the i node is read into a main memory of the computer. When it is required to add a new block to the file to newly add data to the file, the UNIX operating system records the allocation of the new block only in the i node of the main memory and the updating of the i node of the external memory is postponed to reduce its overhead. Such a UNIX operating system as operates in the aforementioned manner is disclosed in a book entitled "THE DESIGN OF THE UNIX OPERATING SYSTEM", written by M. J. Bach, pp. 100-103 (1986). Under this condition, when the computer becomes faulty and stops during writing operation of the data into the external memory, the contents of the i node in the main memory are lost and the i node of the external memory is not updated yet, which results in that information on which block was newly allocated to which block is lost and it becomes impossible to extract data concerning the newly added block after the start of use of the file.
Further, in order to prevent the loss or missing of control information of the file even when a failure occurs in the computer, there has been provided a file storage method for leaving such an operational record as a block addition to a file in an external memory simultaneously with the writing operation of user's data in the external memory. Such a file storage method as carried out in the aforementioned manner is disclosed in a book entitled "INSIDE THE Windows NT File System", written by H. Custer, pp. 36-43 (1994). In this method, even a failure takes place in a computer, it can be avoided that control information of a file is lost. This method is however disadvantageous in that the number of write requests to the external memory is increased and thus overhead at the time of writing data in the file is also increased, because an area for storage of user's data on the external memory is separated from an area for storage of its operational record thereon.