JP2007087063A - Fat file system, file management method, program and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a file system for searching a cluster position for the data main body of a file whose operation is instructed with a few calculation amounts without using many memory sources when performing a reading or writing operation to a file on a storage medium. <P>SOLUTION: In a file system, when an operation instruction is operated to a file designated by a user program 101, a cluster position in a disk 107 for the data of a file whose operation is instructed by a file operation part 103 is calculated by referring to a retrieved start cluster position and FAT data(file allocation table) and FAT cache data. In this case, when new FAT cache data are generated, the FAT cache data are updated to the generated FAT cache data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a file system, a file management method, a program, and a storage medium that manage files using a file allocation table (FAT).

  A file system that manages files using a file allocation table is generally called a FAT file system. A disk medium formatted on the assumption that it is used in a FAT file system is generally called a FAT disk (see, for example, Patent Document 1).

  In this FAT type disk, input / output of user programs is performed in units called sectors. The sector size is typically 512 bytes (or a power thereof).

  A collection of powers of 2 (1, 2, 4, 8, 16, .. j) is called a cluster, and a file is represented by a collection of clusters. How many sectors a cluster is composed of ( Hereinafter, it is represented by the number of sectors / clusters) depending on the disk.

  As a format example of the FAT type disc, a format employed in MS-DOS (registered trademark) will be described with reference to FIGS. FIG. 6 is a diagram showing an example of a format of a FAT type disc adopted in MS-DOS (registered trademark). FIG. 7 is a view showing the structure of the FAT area 302. FIG. 8 is a diagram showing the structure of a directory entry corresponding to one file in the root directory area 303. FIG. 9 is a diagram showing a relationship among the FAT area 302, the root directory area 303, and the data area 304 with respect to one file.

  In the format of the FAT type disk adopted in MS-DOS (registered trademark), as shown in FIG. 6, a boot sector (reserved area) 301, a plurality of FAT areas 302, and a root directory area 303 are provided for the disk. , A data area 304 is provided. The boot sector (reserved area) 301 is the head sector (logical sector number 0), and is an area outside file management. In the boot sector 301, information such as a boot program for loading an operating system, the number of sectors / clusters described above, the number of sectors used in a FAT area described later, and the number of root directory entries are recorded.

  The FAT area 302 is an area for recording a FAT item indicating the location of the cluster and the allocation (allocation) status of the cluster to the file body (contents). The FAT area 302 is duplicated. That is, as the FAT area 302, two areas FAT1 and FAT2 are provided, and the same contents are recorded in each area. Each FAT area 302 is continuously arranged on the disk.

  Some FAT-type discs that are currently widely used currently use 12 bits, 16 bits, or 32 bits to indicate a FAT item for one cluster. Here, the case of 16 bits will be described. Specifically, in the FAT area 302, as shown in FIG. 7, the position of the cluster managed for each FAT item and the usage status of the cluster are shown. The initial value corresponding to the case where the cluster usage status is unused is 0000h.

  Here, when a cluster is assigned to a certain file for the first time, the content of the corresponding FAT item is changed to FFFFh indicating that it is in use and is the last cluster. If the file size is insufficient for one cluster, the content of this FAT item is changed to a cluster number indicating the position of the newly allocated cluster (the content of the FAT item of the newly added cluster is , FFFFh). Thereby, new clusters can be assigned to one file one after another.

  A root directory area 303 is an area for managing the location of a file. An item corresponding to one file consists of 32 bytes. Specifically, as shown in FIG. 8, information such as the file name, size (file size), and the top cluster (start cluster) number of the file is recorded in the root directory area 303.

  The data area 304 is an area for recording information relating to actual file contents (data body) and directories belonging to the root directory and below. The data area 304 is managed in units of clusters, and information about which cluster belongs to which file or is unused is managed by the FAT area 302. The group of clusters belonging to one file need only be logically continuously connected by the FAT area 302, and need not be physically continuously connected.

  Here, for example, for one file, the FAT area 302, the root directory area 303, and the data area 304 have a relationship as shown in FIG. The starting cluster number of the root directory area 303 indicates an item in the FAT area 302, and the FAT area 302 indicates a cluster number in the data area 304 used by the file. In this way, the cluster group constituting one file is logically connected by connecting FAT as a chain.

  Next, reading (or writing) processing of file contents from the FAT type disk will be described with reference to FIG. FIG. 10 is a flowchart showing a procedure for reading (or writing) the file contents from the FAT type disk. Here, in order to simplify the explanation, it is assumed that the number of sectors / clusters is one.

  First, in step S1001, the name, the read (or write) position (byte unit), the read (or write) size (byte unit), and the read data are read out by the user program according to the user program. An area for storing (or storing data to be written) is designated.

  Next, in step S1002, based on the designated read (or write) position, the number of clusters from the beginning of the FAT chain of the file is determined by calculation. The following equation (1) is used for this calculation.

[Reading position] / ([Sector size] × [Sector / number of clusters]) (1)
Here, the value of the cluster obtained by the quotient of the above equation (1) is obtained. Here, the obtained cluster value is n.

  Next, in step S1003, the start cluster number next is acquired from the corresponding file name item in the root directory area 303, and in the subsequent step S1004, the initial value is set to the processed cluster number i indicating the number of clusters that have been processed. Is set as 1.

  Next, in step S1005, the value n obtained in step S1002 is compared with the processed cluster number i in step S1004 to determine whether or not they are equal. If the two values are not equal, the sector in which the start cluster number next is recorded is read in step S1006, and the next cluster number in the FAT chain is set as the start cluster number next in step S1007. . In step S1008, the number i of processed clusters is incremented by 1, and the process returns to step S1005.

  In this manner, the processing from step S1006 to step S1008 is repeated until the number of processed clusters i is equal to the number of clusters n obtained in step S1002 in step S1005. Thereby, the cluster number including the data of the file position specified by the user program can be acquired.

If it is determined in step S1005 that the processed cluster number i is equal to the cluster number n obtained in step S1002, the process proceeds to step S1009. In this step, a sector number corresponding to the obtained cluster number next is designated, and data is actually read (or written) from the disk. Then, this process ends.
JP 2001-101064 A

  However, in the case of the conventional FAT file system, due to its nature, every time data is read (or written) for a certain file, the designated data position is the data area as pre-processing of the actual data reading or writing operation. It is necessary to determine the number of the cluster in 304 by following the FAT chain in order from the start cluster.

  In addition, in the case of a FAT type disk, information on clusters used by one file may be scattered in the FAT area 302 because of the mechanism of managing the allocation status of clusters to each file in the FAT area. . Therefore, in order to acquire a FAT chain of a certain file, it is necessary to read several sectors from the FAT area 302. In particular, when handling a file with a large file size such as moving image data, it is necessary to read out more sectors in the FAT area in order to obtain the cluster number including the data at the specified file position, and the corresponding cluster. It is necessary to repeatedly execute the calculation for obtaining the number. As a result, extra time is required for one read or write process.

  Regarding the reading of the sector in the FAT area, a method of reducing the overhead required for reading the FAT data from the disk by temporarily storing the FAT data once read in the memory can be considered. A method of temporarily holding the FAT chain once obtained in the memory is also conceivable. However, in an environment where the amount of usable memory resources is limited, the above method is not necessarily an effective method.

  The present invention has been made in view of the above-described problems. When a read or write operation is performed on a file on a storage medium, an operation instruction is performed without using a large amount of memory resources and with a small amount of calculation. It is an object of the present invention to provide a file system, a file management method, a program, and a storage medium capable of obtaining a cluster position with respect to a data body of a file that has been recorded.

  In order to achieve the above object, the present invention refers to a file allocation table in which FAT data indicating the correspondence between clusters of storage media and files stored in the storage media is recorded. A file system for managing files, a storage unit for holding one or more FAT cache data used in file operations, a file operation unit for operating instructions for a file designated by a user, and the storage Directory operating means for acquiring directory information from the medium and searching for a starting cluster position for the file instructed by the file operating means based on the directory information; the searched starting cluster position; FAT of the file allocation table Data and the FAT key held in the storage means And FAT operation means for obtaining a cluster position in the storage medium with respect to the data body of the file instructed by the file operation means with reference to the cache data, and the FAT operation means generates new FAT cache data. A file system is provided for performing update processing for updating the FAT cache data held in the storage means to the generated FAT cache data.

  In order to achieve the above object, the present invention refers to a file allocation table in which FAT data indicating the correspondence between clusters of storage media and files stored in the storage media is recorded. A file management method for managing files, a file operation step for instructing an operation for a file designated by a user, directory information is obtained from the storage medium, and operation is performed by the file operation means based on the directory information A directory operation process for searching for a starting cluster position for the indicated file, and the searched starting cluster position, the FAT data of the file allocation table, and one or more FAT cache data held in the storage means Data of the file instructed for operation in the file operation step. A FAT operation step for obtaining a cluster position in the storage medium with respect to a main body. In the FAT operation step, new FAT cache data is generated, and the FAT cache data held in the storage means is generated. Provided is a file management method characterized by performing an update process for updating to FAT cache data.

  In order to achieve the above object, the present invention refers to a file allocation table in which FAT data indicating a correspondence relationship between a cluster of storage media and files stored in the storage media is referred to, and the files in the storage media A file management module for instructing an operation for a file designated by a user, directory information is obtained from the storage medium, and the file operation is performed based on the directory information. A directory operation module for searching a start cluster position for a file instructed by the means; the searched start cluster position; FAT data of the file allocation table; and one or more FAT cache data held in a storage means To refer to the file operation module. A FAT operation module for obtaining a cluster position in the storage medium with respect to the data body of the file instructed by the operation, the FAT operation module generates new FAT cache data and is held in the storage means There is provided a program for performing update processing for updating FAT cache data to the generated FAT cache data.

  In order to achieve the above object, the present invention provides a storage medium characterized by storing the program according to claim 7 in a computer-readable manner.

  According to the present invention, when a read or write operation is performed on a file on a storage medium, the cluster position with respect to the data body of the file that is instructed to operate without using many memory resources and with a small amount of calculation Can be sought.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a software configuration of a FAT file system according to an embodiment of the present invention.

  As shown in FIG. 1, the FAT file system is constructed by a FAT file system program 102 that realizes the FAT cache management system. The FAT file system program 102 includes a file operation unit 103, a directory operation unit 104, and a FAT operation unit 105.

  The file operation unit 103 manages file descriptors and performs processing in response to a request from the user program 101. The file operation unit 103 performs, for example, processing for opening or closing a file specified by a file name or the like, creation of a new file, management of a file pointer indicating from which position in the file space a read or write operation is performed, etc. Do.

  The directory operation unit 104 analyzes directory entry information read from the disk (storage medium) 107 via the disk driver unit 106. In addition, the directory operation unit 104 analyzes and updates a directory entry. For example, a file instructed by the user program 101 is searched, a cluster (starting cluster) number including data corresponding to the head of the file is acquired, and the latest file information is written to the directory entry.

  The FAT operation unit 105 constructs, updates, and deletes FAT cache data on a memory. Further, the FAT operation unit 105 refers to the FAT cache data or analyzes the directory entry and the FAT area information read from the disk 107, and determines the cluster on the disk 107 from the file position of the file to be read / written. Get the number. Further, the FAT operation unit 105 performs processing such as correctly forming the FAT chain of the file and writing it to the disk 107.

  Here, the disk 107 is a storage medium such as a floppy (registered trademark) disk, a hard disk, or a flash memory card. The disk drive unit 106 reads the actual data content of the disk 107 or writes data to the disk 107.

  Next, a hardware configuration for realizing the FAT file system of the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram showing a hardware configuration for realizing the FAT file system of FIG.

  As shown in FIG. 2, the FAT file system of the present embodiment includes a CPU 201, a RAM 202, a disk device 203 having a disk 107, and a system bus 204 for connecting them. The disk device 203 is a storage device including the disk driver unit 106 and the disk 107 (shown in FIG. 1). The disk 107 stores various programs including the user program 101, the FAT file system program 102, and the disk driver unit 106, and files such as data and images created by the user. The CPU 201 reads out the user program 101, the FAT file system program 102, and the disk driver unit 106 from the disk device 203, loads them on the RAM 202, and executes them. As a result, a FAT file system that implements the FAT cache management system is constructed.

  Next, the FAT cache operated by the FAT operation unit 105 will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of the FAT cache operated by the FAT operation unit 105 of FIG.

  In one FAT cache, as shown in FIG. 3, an index value that can uniquely specify a file existing on a disk, a cluster number of one of the clusters constituting the file, and the cluster number are included. Contains the cumulative number of clusters from the beginning of the corresponding file. In addition, in order to manage a plurality of FAT cache data, by storing a memory address indicating the next FAT cache data, the FAT cache data forms a chain, and the plurality of FAT cache data can be processed in order. enable. In the last data in the FAT cache chain, 0 is recorded at the memory address indicating the next FAT cache data.

  Next, a file content read (or write) process by the FAT file system of this embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing the procedure of a file content read (or write) process by the FAT file system of this embodiment. Here, it is assumed that the recording format of the FAT disc, the configuration of the directory entry, and the configuration of the FAT area used for the description are the same as those shown in FIGS. 6 to 8 described in the conventional example.

  First, in step S801, the user program 101 performs the read (or write) file name, read (or write) position (byte unit), read (or write) size (byte unit), and read data. Is specified (or the data to be written is stored).

  Next, in step S802, based on the designated read (or write) position, the number of clusters from the beginning of the FAT chain of the file is determined by calculation. In step S803, the start cluster number next is acquired from the corresponding file name item in the root directory area 303. In subsequent step S804, 1 is set as an initial value to the processed cluster number i indicating the number of clusters for which processing has been completed.

  Next, in step S805, the value n obtained in step S802 is compared with the processed cluster number i in step S804, and it is determined whether or not they are equal. If the two values are not equal to each other, FAT cache data is searched in step S806. Here, with reference to the FAT cache chain (shown in FIG. 3), a search is made for the closest value with the number of clusters n or less with respect to the number of clusters i. In step S807, it is determined whether or not there is corresponding cache data from the search result in step S806. If there is corresponding FAT cache data, the number of clusters and the cluster number of the corresponding FAT cache data are set as the initial value of the processed cluster number i and the initial value of the start cluster number next in step S808, respectively. Is assigned as

  Next, in step S809, the value n obtained in step S802 is compared with the processed cluster number i in step S808 to determine whether or not they are equal. If the two values are not equal to each other, the sector in which the start cluster number next is recorded is read in step S810, and the next cluster number in the FAT chain is set as the start cluster number next in step S811. .

  Next, in step S812, FAT cache updating is performed to save information (shown in FIG. 3) such as the cumulative cluster number and cluster number in the FAT cache. Details of the FAT cache update will be described later. In step S813, the number of processed clusters i is incremented by 1, and the process returns to step S809.

  In this way, the processing from step S810 to step S813 is repeated until the processed cluster number i becomes equal to the cluster number n obtained in step S802 in step S809.

  If it is determined in step S809 that the processed cluster number i is equal to the cluster number n obtained in step S802, a sector number corresponding to the obtained cluster number next is designated in step S814, First, data is read (or written) from the disk 107. Then, this process ends.

  If it is determined in step S807 that there is no corresponding FAT cache data, the process skips step S808 and proceeds to step S808.

  If it is determined in step S805 that the value n obtained in step S802 is equal to the number i of processed clusters in step S804, the process proceeds to step S814.

  Thus, before performing the iterative process from step S809 to step S813, a part of the iterative process can be omitted by searching the FAT cache data in step S806. As a result, the cluster number for the operation purpose can be obtained at high speed.

  Next, the FAT cache update process in step S812 will be described with reference to FIG. FIG. 5 is a flowchart showing the procedure of the FAT cache update process in step S812 of FIG.

  In the present embodiment, the FAT cache data is updated at regular intervals specified in advance by the user program 101 or the like. For example, if the cache interval is specified as a size in bytes, the [specified interval (byte)] / ([sector size] ra [sector / cluster count]) is calculated and the quotient is cached by the cluster It is calculated | required as space | interval s. Further, the number of FAT caches is limited, and when the contents of old FAT cache data are updated to new ones, those having the oldest reference time of the cached data are replaced. That is, the FAT cache data is updated by an algorithm using so-called LRU (Least Recently Used).

  In this FAT cache update process, as shown in FIG. 5, first, in step S901, the first FAT cache data (c) in the FAT cache chain is acquired. Next, in step S902, it is determined whether or not the content of the acquired FAT cache data (c) is empty (invalid). If the content of the acquired FAT cache data (c) is not empty (invalid), it is determined in step S903 whether the acquired FAT cache data (c) is the last data in the FAT cache in. . If the acquired FAT cache data (c) is not the last data in the FAT cache-in, the next FAT cache data (c) in the FAT cache chain is acquired in step S904, and the process returns to step S902.

  When it is determined that the content of the FAT cache data (c) acquired in step S902 is empty (invalid), or the FAT cache data (c) acquired in step S903 is the last data in the FAT cache in. If it is determined that there is, in step S905, it is determined whether or not the value of the cumulative number of clusters n of the FAT cache data to be stored is a multiple of the interval s for storing as FAT cache data. If the value of the cumulative cluster number n is not a multiple of the interval s, this process ends.

  On the other hand, if the value of the cumulative cluster number n is a multiple of the interval s, FAT cache data including the cumulative cluster number, cluster number, etc. is recorded in step S906. In the subsequent step S907, the FAT cache chain is updated (replaced) by an algorithm based on the LRU. Then, this process ends.

  In the present embodiment, all of the acquired clusters are obtained in the FAT cache in step S812 until the cluster that is the target of the read / write operation is obtained by the processing of tracing the FAT chain from step S809 to step S813. It becomes the target of update processing. Therefore, in this case, for example, when data is read by skipping the file reading position larger than the previous reading position, the FAT chain cluster in the middle is stored as FAT cache data.

  However, if there is no such need, the FAT cache update process in step S812 may be performed after YES in step S809.

  An object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the embodiment to a system or apparatus, and the computer (or CPU, MPU, etc.) of the system or apparatus is stored in the storage medium. It is also achieved by reading and executing the program code.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. -RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM, etc. can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the computer based on the instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included.

  Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Further, by executing the program code read out by the computer, not only the functions of the above-described embodiments are realized, but also the OS running on the computer based on the instruction of the program code is actually Needless to say, the present invention also includes a case in which the functions of the above-described embodiments are realized by performing part or all of the processing and the processing.

  In this case, the program is supplied by downloading directly from a storage medium storing the program or from another computer or database (not shown) connected to the Internet, a commercial network, a local area network, or the like.

  The form of the program may be in the form of object code, program code executed by an interpreter, script data supplied to an OS (operating system), and the like.

It is a block diagram which shows the software structure of the FAT file system which concerns on one embodiment of this invention. It is a block diagram which shows the hardware constitutions for implement | achieving the FAT file system of FIG. It is a block diagram which shows the structure of the FAT cache which the FAT operation part 105 of FIG. 1 operates. It is a flowchart which shows the procedure of the reading (or writing) process of the file content by the FAT file system of this Embodiment. 5 is a flowchart showing a procedure of FAT cache update processing in step S812 of FIG. It is a figure which shows an example of the format of the FAT type disc employ | adopted by MS-DOS (trademark). FIG. 3 is a diagram showing a structure of a FAT area 302. FIG. 3 is a diagram showing a structure of a directory entry corresponding to one file in a root directory area 303. It is a figure which shows the relationship between the FAT area | region 302, the root directory area | region 303, and the data area | region 304 regarding one file. It is a flowchart which shows the procedure of the reading (or writing) process of the file content from a FAT type | mold disk.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 User program 102 FAT file system program 103 File operation part 104 Directory operation part 105 FAT operation part 106 Disk driver part 107 Disk 201 CPU
202 RAM
203 disk unit

Claims (8)

A file system for managing files in the storage medium with reference to a file allocation table in which FAT data indicating a correspondence relationship between a cluster of the storage medium and a file stored in the storage medium is recorded;
Storage means for holding one or more FAT cashier data used in file operations;
A file operation means for instructing operation on a file designated by the user;
Directory operation means for obtaining directory information from the storage medium and searching for a starting cluster position for a file instructed by the file operation means based on the directory information;
The storage medium for the data main body of the file instructed by the file operation means with reference to the searched start cluster position, the FAT data of the file allocation table, and the FAT cache data held in the storage means FAT operation means for obtaining the cluster position in
The file system characterized in that the FAT operation means generates new FAT cache data and performs an update process for updating the FAT cache data held in the storage means to the generated FAT cache data. .   2. The file system according to claim 1, wherein the FAT operation means generates FAT cache data at intervals specified in advance and updates the FAT cache data.   2. The file system according to claim 1, wherein the FAT operation means updates the oldest FAT cache data among the FAT cache data held in the storage means to the generated FAT cache data.   The FAT cache data is counted from at least an index value capable of uniquely specifying a file existing on the storage medium, one cluster number of clusters constituting the file, and a start cluster corresponding to the cluster number. 2. The file system according to claim 1, wherein the cumulative number of clusters is included.   The FAT cache data includes a memory address where a FAT cache data to be referred to next exists, and the FAT cache data is managed so as to form a chain with the next FAT cache data. Item 4. The file system according to Item 4. A file management method for managing a file in the storage medium with reference to a file allocation table in which FAT data indicating a correspondence relationship between a cluster of the storage medium and a file stored in the storage medium is recorded. ,
A file operation process for instructing operation on a file designated by the user;
A directory operation step of obtaining directory information from the storage medium and searching for a start cluster position for a file instructed by the file operation means based on the directory information;
With reference to the searched start cluster position, FAT data of the file allocation table, and one or more FAT cache data held in the storage means, the data body of the file instructed in the file operation step A FAT operation step for obtaining a cluster position in the storage medium,
In the FAT operation step, new FAT cache data is generated, and an update process for updating the FAT cache data held in the storage means to the generated FAT cache data is performed. Method. A program for constructing a system for managing files in the storage medium by referring to a file allocation table in which FAT data indicating a correspondence relationship between a cluster of the storage medium and a file stored in the storage medium is recorded Because
A file operation module for instructing operations on a file specified by the user;
A directory operation module that acquires directory information from the storage medium and searches for a start cluster position for a file that is instructed by the file operation means based on the directory information;
With reference to the searched start cluster position, the FAT data of the file allocation table, and one or more FAT cache data held in the storage means, the data body of the file instructed by the file operation module A FAT operation module for determining a cluster position in the storage medium,
The FAT operation module generates new FAT cache data, and performs an update process for updating the FAT cache data held in the storage unit to the generated FAT cache data.   A storage medium storing the program according to claim 7 in a computer-readable manner.

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