JP2011118623A - Data synchronization apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce disk input/output processing to a FAT area which requires data updating when performing operation for writing or deleting data to/from a file in a FAT type disk. <P>SOLUTION: A data synchronization apparatus includes a means for changing data of an FAT, a means for controlling a temporary storage area when reading out or writing data and a means for writing data corresponding to a data change in a recording medium out of the data stored in the temporary storage area. The data synchronization apparatus reads out data of at least one FAT from the temporary storage area, changes the read data, calculates a position for writing the changed data in the recording medium and a writing position of the other FAT in which the contents of the data are redundantly stored by using the sizes of the FATs, and controls the calculated results so as to be stored in the temporary storage area. Further when rewriting the changed FAT data stored in the temporary storage area in the recording medium, the same data is written in the writing position of the other FAT. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a data synchronization apparatus, and more particularly to a technique suitable for use in a FAT file system.

  A file system that manages file data using a file allocation table (hereinafter referred to as FAT) is generally called a FAT file system. In particular, a recording medium such as a hard disk logically formatted for the FAT file system is called a FAT type disk. When receiving an instruction from the user program and performing operations such as reading and writing data on the FAT type disk, the FAT file system performs input / output in units called sectors. Here, the size of one sector is usually 512 bytes or a power thereof. A set of sectors of powers of 2 (1, 2, 4, 8, 16,...) Is called a cluster, and a file existing on a FAT type disk is represented by a set of clusters. The number of sectors in a cluster is determined at the time of logical formatting of the disk mainly by the capacity of the FAT type disk.

  When a new file is created by the FAT file system, it is performed as follows. First, when an unused cluster is assigned to a file for the first time in order to record data contents, the value of the corresponding FAT item is changed from 0000H indicating unused to FFFFH indicating used and the last cluster. . If data is continuously recorded on the same file, the size of the data content is insufficient for one cluster. Therefore, the value of the FAT item corresponding to the final cluster of the file is changed to a cluster number indicating the position of the unused cluster to be newly added and allocated next. At this time, the value of the FAT item of the newly added unused cluster is changed from 0000H to FFFFH. By repeating this, clusters can be assigned to one file one after another. The same applies when a previously created file exists and data is added to it. On the other hand, when the file size is reduced or the file is deleted, the value of the FAT item corresponding to the cluster which has become unnecessary to be assigned to the file as a result of the operation is changed to 0000H. Then, the value of the FAT item corresponding to the final cluster is changed to FFFFH for the new file size.

  Here, as described above, the data on the disk is input / output in units of sectors. Therefore, when updating the contents of the FAT, a temporary storage area (hereinafter referred to as a buffer) is provided in a semiconductor memory or the like that can input and output at high speed, instead of directly changing data on the disk. Then, the original data on the disk is temporarily stored in the buffer, necessary changes are made to the buffer, and then the buffer contents are written back to the disk as appropriate. Thus, the process of writing back the buffer contents onto the disk is called data synchronization (see, for example, Patent Document 1).

Japanese Patent No. 3703181

  In a FAT type disc, it is necessary to always keep the contents of FAT1 and FAT2 the same. For this reason, when updating the FAT in accordance with an operation such as addition or deletion of data to the file, the contents of FAT1 and FAT2 are once read onto the buffer. Then, it is necessary to perform a process of making the same change to each and then writing back to the disk to synchronize the data.

  Further, in the case of a FAT type disk, there is a possibility that information on clusters used by one file is scattered in the FAT area because of the mechanism of managing the allocation status of clusters to each file in the FAT area. Therefore, even if the file size is small, the number of FAT1 and FAT2 sectors that need to be updated may increase. There is a problem that the input / output operation to the disk which requires a very long processing time as compared with the CPU processing increases, and as a result, the processing time of the entire file operation becomes long.

  In view of the above-described problems, the present invention makes it possible to reduce disk input / output processing to a FAT area that requires data update when performing operations such as writing or deleting data in a file on a FAT disk. The purpose is that.

  A data synchronization apparatus according to the present invention includes an acquisition unit that acquires information on the size of a file allocation table, a FAT processing unit that changes data in the file allocation table, and a temporary storage area when data is read or written. Buffer control means for performing control, and synchronization means for writing to a recording medium in accordance with a change in data among data stored in the temporary storage area, and the FAT processing means includes at least one file allocation table A file allocation table in which data is read from the temporary storage area and changed, and a position at which the changed data is written to the recording medium and a write position of another file allocation table that stores the same contents are acquired by the acquisition unit. Is calculated using the size of The buffer control means is controlled to store in the temporary storage area, and the synchronization means writes the changed file allocation table data stored in the temporary storage area to the recording medium when the other file is written back. It is characterized in that the same data is written to the write position of the allocation table.

  According to the present invention, it is possible to omit the process of reading one of the overlapping file allocation tables onto the buffer. As a result, operations such as writing file data and deleting files can be performed at a higher speed.

It is a block diagram which shows the function structural example of a data synchronizer. It is a block diagram which shows the hardware structural example of a data synchronizer. It is a figure which shows an example of the format of a FAT type | mold disk. It is a figure which shows the structural example of a FAT area | region. It is a figure which shows an example of the information currently recorded on the root directory area | region. It is a figure which shows the structural example of a buffer. It is a flowchart which shows an example of the update process procedure of FAT. It is a flowchart which shows an example of the procedure of the synchronization process of buffer data.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a functional configuration example of a data synchronization apparatus in a FAT file system using a file allocation table (FAT) according to the present embodiment.
In FIG. 1, 101 is a user program that uses the FAT file system, and 102 is a FAT file system program that implements the FAT data synchronization system according to the present embodiment. A file process 103 receives a request from the user program 101, manages a file descriptor, opens and closes a file specified by a file name, and manages a file pointer for creating, reading, and writing a new file. Part.

  A directory processing unit 104 analyzes the directory entry information read from the disk and searches for the existence of a file designated by the user program 101. Further, the directory processing unit 104 obtains a cluster (start cluster) number including the data of the head portion of the file, and performs analysis and update of the directory entry such as writing the latest file information in the directory entry. A FAT processing unit 105 obtains a cluster number on the disk from the file position of the file to be read and written by analyzing information on the directory entry and the FAT area. Further, the FAT processing unit 105 performs processing such as adding data to a file or deleting a file and correctly forming the FAT chain of the file and writing it in the FAT area.

  A buffer 106 performs processing to return data of a designated sector stored in a buffer of a temporary storage area to be internally managed to a request source in response to requests from the file processing unit 103, the directory processing unit 104, and the FAT processing unit 105 It is a control unit. The buffer control unit 106 also performs processing for writing back the buffer contents changed according to the instruction to the disk. Reference numeral 107 denotes a disk driver unit that reads out various data from a disk (recording medium) 108 of a recording medium such as a hard disk or a flash memory card as an actual data storage area or writes data to the disk 108.

FIG. 2 is a block diagram illustrating a hardware configuration example of the data synchronization apparatus according to the present embodiment.
In FIG. 2, 201 is a CPU that loads and executes the above-described user program 101 and FAT file system program 102. Reference numeral 202 denotes a RAM which stores a program for causing the above-described user program 101, FAT file system program 102, and disk driver unit 107 to function. Further, the RAM 202 is used as a buffer area when the buffer control unit 106 reads or writes data on the disk 108. In addition, it is used as a work area for saving or saving various variables used during the operation of each software program. Reference numeral 203 denotes a disk device for reading from and writing to the FAT disk 108 serving as a file data storage area. A system bus 204 connects the CPU 201, RAM 202, and disk device 203.

FIG. 6 is a diagram illustrating a configuration example of a buffer controlled by the buffer control unit 106.
In FIG. 6, the buffer is divided into a status bit 601 indicating the status of the buffer, a sector number 602 where the contents of the buffer exist, and a data 603 main body to be copied from the disk 108 to the buffer. The status bit 601 includes a dirty bit indicating that the buffer content needs to be written to the disk 108. The other states are arbitrary. The buffer having the above configuration secures a sufficient area on the RAM 202 for the user program 101 to operate.

  Next, the FAT update processing operation by the FAT file system in this embodiment will be described. It should be noted that the recording format, directory entry structure, and FAT area structure of the FAT type disk 108 in this embodiment are shown in FIGS. 3, 4 and 5, respectively.

FIG. 3 is a diagram showing an example of the format of the FAT disk, and the basic structure is the same as that adopted in MS-DOS (registered trademark).
In FIG. 3, reference numeral 301 denotes a boot sector indicating the first sector (logical sector number 0). 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.

  Reference numeral 302 denotes a FAT area, which is an area for recording a FAT item indicating the next cluster number following the cluster number, which serves both as the location of the cluster and the allocation (allocation) status of the cluster to the file body (content). The FAT area 302 is duplicated to ensure safety, and the first FAT area (hereinafter, FAT1) and the second FAT area (hereinafter, FAT2) in FIG. 3 always have the same contents. Things are going to be recorded. FAT1 and FAT2 are continuously arranged on the disk.

FIG. 4 is a diagram illustrating a structure example of the FAT area 302. Some FAT-type discs that are currently widely used use 12 bits, 16 bits, or 32 bits to indicate a FAT item for one cluster. In this embodiment, the case of 16 bits is used. Explained as an example.
In FIG. 4, the position from the top of each FAT item corresponds to the position of the cluster managed by that item as it is. The initial value of each item is 0000H (hexadecimal number 0), which indicates an unused state.

  Returning to the description of FIG. 3, reference numeral 303 denotes a root directory area, which is an area for managing the location of a file. An item corresponding to one file is expressed by 32 bytes. In the root directory area 303, as shown in FIG. 5, information such as the name and size of the file (file size) and the first cluster (starting cluster) number including the data of the file are recorded. .

  Reference numeral 304 denotes a data area in which information about the actual file contents (data body) and the directory belonging to the root directory is recorded. Similar to the FAT area 302, the data area is managed in units of clusters, and information such as the order of connection between the file to which the cluster belongs and the cluster, or an unused cluster is managed by the FAT area 302. Accordingly, the order of connection between clusters and clusters belonging to a certain file is logically continuously connected by the FAT area 302. In the data area 304, data of one file is not necessarily physically connected. It is not always continuous. The number of FAT sectors indicating the size of one FAT area is obtained from the boot sector 301 when the file processing target disk is first accessed, and is already stored in the RAM 202. It shall be.

FIG. 7 is a flowchart illustrating an example of a FAT update processing procedure according to the present embodiment.
First, in step S701, under the control of the FAT processing unit 105, the buffer control unit 106 stores the sector number in which the FAT item to be updated is present in the sector number 602 in FIG. In addition, although it exists in both FAT1 and FAT2 as shown in FIG. 3 on the disk 108, the corresponding sector number in the range of FAT1 is stored here.

  Next, in step S702, the buffer control unit 106 writes the sector number data stored in step S701 into the data 603 in FIG. In step S703, the buffer control unit 106 changes the corresponding FAT item as instructed on the buffer written in step S702. In step S704, the buffer control unit 106 sets the dirty bit of the status bit 601 to end the process to indicate that the change has been made.

On the other hand, the buffer synchronization processing is appropriately performed by an instruction from the user program 101 at an arbitrary timing. FIG. 8 is a flowchart illustrating an example of a procedure of buffer data synchronization processing. 8 is performed under the control of the buffer control unit 106.
First, in step S801, the dirty bit of the status bit 601 is referred to and it is determined whether or not the buffer is of a sector that needs to be written to the disk 108. If writing to the disk 108 is not necessary, the process proceeds to step S805.

  On the other hand, if it is determined in step S801 that the sector needs to be written to the disk 108, the process proceeds to step S802. Then, referring to the sector number 602 of the buffer, the disk driver unit 107 is instructed to write the data 603 to the sector in the appropriate FAT1 area. Next, in step S803, the corresponding sector number of FAT2 is calculated from the FAT size n obtained in advance. Specifically, the sector number 602 is added with the FAT size n.

  In step S804, the disk driver unit 107 is instructed to write the buffer data 603 instructed to be written in step S802 to the sector in the corresponding FAT2 area obtained in step S803. In step S805, it is determined whether or not processing has been completed for all buffers. If not completed, the process returns to step S801. If completed, the process ends. As described above, the processing from step S801 to step S804 is repeated for all buffers. In this way, the contents of the FAT2 area are not read into the buffer at all, and the FAT data changed in accordance with the file operation such as addition writing or deletion of data to the file is written to both FAT1 and FAT2. be able to.

  In the present embodiment, the buffer secured in the RAM 202 with the configuration shown in FIG. 6 is dedicated to FAT data. However, this buffer may be used as a buffer common to the directory entry data and file data buffers. In this case, a FAT bit is provided in the status bit 601 to indicate that the buffer is distinguished from directory entry data and file data. The same effect can be obtained by writing the data 603 of the same buffer to the corresponding sector of FAT2 only when the FAT bit is set (for example, other than zero) with reference to the status bit 601 during the buffer synchronization operation. can get.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

105 FAT processing unit, 106 buffer control unit, 107 disk driver unit, 108 disk

Claims (1)

An acquisition means for acquiring size information of the file allocation table;
FAT processing means for changing data in the file allocation table;
Buffer control means for controlling the temporary storage area when reading or writing data;
Of the data stored in the temporary storage area, having synchronization means for writing to the recording medium in accordance with the data change,
The FAT processing means reads and changes data in at least one file allocation table from the temporary storage area, and stores the same content as the position where the changed data is written to the recording medium. Calculating the write position using the size of the file allocation table acquired by the acquisition means, and controlling the buffer control means to store in the temporary storage area,
The synchronization means writes the same data to the write position of the other file allocation table when the changed file allocation table data stored in the temporary storage area is written back to the recording medium. Synchronizer.

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