JP2012088842A - File management device, file management method, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a high-speed search for a location of a directory entry in which a newly created file is recorded.SOLUTION: If there is not a directory entry that is not used even once in newly creating a file in a directory, a reusable directory entry is searched for by using location information (a cluster number 109 and an offset 110) of directory entries of deleted files, and the directory entry is reused. Furthermore, if a reusable directory entry does not exist, a directory entry with a file deleted is searched for out of reused directory entries.

Description

  The present invention relates to a file management apparatus, a file management method, and a computer program, and is particularly suitable for use in searching for a directory entry that records a newly created file.

Regarding the method of searching for the location of a directory entry that records the name of a file to be newly created, the background art will be described by taking the case of a FAT (File Allocation Table) file system as an example.
In the FAT file system, directory entries in which file names and other metadata are recorded are bundled with those belonging to the same directory, and as in the case of data such as texts or images, It is managed as a chain.

When a new file is to be created in a certain directory on the file system, unused directory entries are used sequentially from the beginning of the cluster and are filled without any gaps. If the directory entry is used to the end of the cluster, a new cluster is allocated for the directory.
On the other hand, once a file has been deleted, the directory entry corresponding to that file is marked as deleted, and that directory entry can be reused for new files later. (See Patent Document 1).

As described above, when a new file is created, there are a case where a directory entry that has never been used in the past and a case where a directory entry of a deleted file is reused.
In general, after using up to the last directory entry of a directory, in order to efficiently use the capacity of the storage medium, first delete the directory entry marked as deleted from the beginning of the directory. look for. A new cluster is allocated only if no reusable directory entry is found.

Japanese Patent Laying-Open No. 2005-242707

However, there is the following problem when searching for a directory entry that can be reused from the beginning of the directory after the directory entry that has never been used is used up. That is, there is a problem that the time consumed for searching the entire directory increases linearly according to the number of files already existing in the directory. Furthermore, if there is no directory entry that can be reused in the directory as a result of searching the entire directory, there is a problem that the time consumed for searching the entire directory is eventually wasted.
The present invention has been made in view of the above problems, and an object thereof is to search at high speed the position of a directory entry for recording a newly created file.

  The file management apparatus of the present invention is a file management apparatus that records a file in a directory and deletes a file recorded in the directory, and when the file is deleted, the deleted file belongs. A storage means for storing a set of information for specifying a directory, information for specifying a directory entry used by the deleted file in a storage medium, and a directory to which the deleted file belongs, And recording means for recording the new file in a directory entry specified by the information stored by the storage means when recording the new file.

  According to the present invention, a new file is recorded in the directory entry specified by the information specifying the directory to which the deleted file belongs and the information specifying the directory entry used by the deleted file. I did it. Therefore, the position of the directory entry for recording a newly created file can be searched at high speed.

It is a figure which shows the structure of a file system apparatus. It is a figure which shows the recording format of a FAT type disc. It is a figure which shows notionally one structure of a directory entry. It is a figure which shows arrangement | positioning of a directory entry. It is a flowchart explaining the 1st example of the process at the time of deleting a file. It is a flowchart explaining the process at the time of creating a new file. It is a flowchart explaining the 2nd example of the process at the time of deleting a file.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
First, the first embodiment will be described. FIG. 1 is a diagram illustrating an example of a configuration of a file system apparatus that performs file management.
In FIG. 1, 101 is a CPU, 102 is a storage medium, 103 is a bus, 104 is an application unit, 105 is a file system unit, 106 is a file deletion processing unit, 107 is a new file creation processing unit, and 108 is reusable directory entry information. It is. The application unit 104 and the file system unit 105 are configured using computer programs and data arranged in, for example, a ROM and a RAM. The functions of the application unit 104 and the file system unit 105 are realized by the CPU executing this computer program. In FIG. 1, for convenience of explanation, the application unit 104 and the file system unit 105 are shown in a part different from the storage medium 102. However, actually, the application unit 104 and the file system unit 105 are stored in the storage medium 102 (for example, ROM or RAM).

  The reuse directory entry information 108 is information including a set of a cluster number 109, an offset 110, and a flag 111. The cluster number 109 is information for identifying the number of the first cluster in the directory to which the file deleted from the storage medium 102 or the like belongs. The offset 110 is information specifying the position (number of bytes of offset from the head of the directory) where the metadata of the file deleted from the storage medium 102 or the like was recorded. The flag 111 is a flag indicating the current state of the reuse directory entry information 108. The initial value of the flag 111 is a value that indicates invalidity. As the value of the flag 111, in addition to a value indicating invalidity, there are a value indicating validity and a value indicating used. Invalid indicates that there is no reusable directory entry in the corresponding directory. Valid indicates that there is a directory entry that can be reused in the corresponding directory. Used indicates that a file has been recorded in a directory entry that can be reused.

Next, an outline of the FAT file system will be described.
A file system that manages file data on a file system using a file allocation table (FAT) is called a FAT file system. A storage 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 an operation such as reading or writing data of a file existing on the FAT type disk, the input / output is performed in units called sectors. The size of one sector is usually 512 bytes or 512 power bytes.

A set of 2 consecutive sectors (1, 2, 4, 8, 16,...) Is called a cluster. A file existing on a FAT type disk is represented by a set of clusters. The number of sectors (number of sectors / clusters) that one cluster consists of is determined at the time of logical formatting of the disk mainly depending on the capacity of the FAT type disk.
FIG. 2 is a diagram showing an example of the recording format of the FAT type disc.
In FIG. 2, a boot sector 201 indicates the first sector (logical sector number 0). The following is recorded in the boot sector 201. In other words, the boot program main body for loading the operating system, the number of sectors / clusters (the number of sectors per cluster), and the maximum number of files (the number of root directory entries) that can be placed directly under the root directory described later are recorded ing. In addition, the boot sector 201 records the total number of sectors of the disk, the number of sectors used in a FAT area described later (the number of sectors per FAT), logical format information, and the like.

The FAT area 202 is an area for recording a status of cluster allocation (allocation) to a file and a cluster chain status. For safety, the FAT area 202 is duplicated as shown in FIG. 2 and is continuously arranged on the disk (see FAT1 and FAT2 in FIG. 2). That is, the same contents are always recorded in FAT1 and FAT2.
The root directory area 203 is an area for recording a file existing on the root directory or a directory entry of the root directory.

The data area 204 is an area for recording “file data” or “directory entry of a file belonging to a directory other than the root directory or a directory other than the root directory”.
The data area 204 is managed in units of clusters, but the chain of clusters constituting the file or directory is managed by the FAT area 202. Therefore, the file or directory data need not be physically continuous on the FAT type disk.

Hereinafter, in order to simplify the description, it is assumed that one cluster is composed of one sector.
FIG. 3 is a diagram conceptually showing an example of the configuration of one directory entry in the root directory area 203 shown in FIG.
In FIG. 3, the directory entry is composed of 32 bytes. Metadata for the file is recorded as each item of the directory entry. Specifically, the name, extension, attribute, creation date / time or last update date / time, top cluster number, file size, etc. of the file or directory (subdirectory) existing on the root directory of the FAT disk are stored. Here, the attributes include save, directory, volume label, system file, hidden, and read-only bit values. The head cluster number is the number of the first cluster constituting the file. The file size is the size of the file expressed in bytes.
Note that the structure of the directory entry of the subdirectory created under the root directory also conforms to the directory entry of the root directory.

FIG. 4 is a diagram illustrating an example of the arrangement of directory entries in the root directory area 203.
Normally, each time a new file is created, the directory entry is filled with the metadata of the new file from the lower address of the root directory area 203. A directory entry in which file metadata has not yet been recorded has at least the first byte of the directory name filled with 00h (hexadecimal number). Further, the fact that the first byte of the name of the directory is E5h indicates that the directory is a directory in which the file is deleted after the file is once created.
Note that the arrangement of the directory entries of the subdirectories created on the root directory also conforms to the arrangement of the directory entries.

Hereinafter, an example of processing of the file system apparatus when deleting an existing file will be described with reference to the flowchart of FIG.
First, in step S501, the file deletion processing unit 106 reads the data of the first cluster of the directory to which the file designated by the application unit 104 belongs and writes it in the system RAM.
Next, in step S502, the file deletion processing unit 106 performs the following processing. That is, whether the name and extension recorded in the first 32 bytes (first directory entry) of the data of the first cluster written in the RAM match the name and extension of the file specified from the application unit 104. Determine whether or not. As a result of the determination, if the name and the extension match, the process proceeds to step S503, and if not, the process proceeds to step S505.

In step S503, the file deletion processing unit 106 deletes the file specified by the application unit 104 from the directory, and writes E5h in the first byte (name head) of the directory entry of the directory.
Next, in step S504, the file deletion processing unit 106 stores the first cluster number (cluster number 109) of the directory being operated and the position (offset 110) where the directory entry is recorded as the reuse directory entry information 108. To do. Further, the file deletion processing unit 106 updates the flag 111 with a value indicating validity. And the process by the flowchart of FIG. 5 is complete | finished.

On the other hand, when the process proceeds from step S502 to step S505, the file deletion processing unit 106 advances the directory being operated by one.
In step S506, the file deletion processing unit 106 determines whether all valid directory entries included in the directory to which the file specified by the application unit 104 belongs have been checked. For example, when a directory entry whose name starts with 00h appears, or when the number of selected directory entries reaches the number of directory entries that fit in one cluster, it is determined that all valid directory entries have been checked. . As a result of the determination, when all the valid directory entries have been examined, the processing according to the flowchart of FIG. 5 is terminated. On the other hand, if all the valid directory entries have not been examined, the process returns to step S502, and the processes after step S502 are performed on the directory specified in step S505.

Next, an example of processing of the file system apparatus when creating a new file will be described with reference to the flowchart of FIG.
First, in step S601, the new file creation processing unit 107 reads the data of the first cluster of the directory in which the file designated by the application unit 104 is to be created, and writes it in the system RAM.
In step S602, the new file creation processing unit 107 determines whether the value of the first byte of the directory entry of the first cluster written in the RAM is 00h. That is, the new file creation processing unit 107 determines whether or not the directory entry of the first cluster written in the RAM is an unused directory entry. As a result of the determination, if the value of the first byte of the directory entry of the first cluster is 00h (if it is an unused directory entry), the process proceeds to step S603, and if not, the process proceeds to step S604.

In step S603, the new file creation processing unit 107 records metadata for the new file in the directory entry being operated. And the process by the flowchart of FIG. 6 is complete | finished.
On the other hand, in step S604, the new file creation processing unit 107 advances the directory being operated by one.
Next, in step S605, the new file creation processing unit 107 determines whether or not all valid directory entries included in the directory to which the file specified by the application unit 104 belongs have been investigated. For example, when the number of selected directory entries reaches the number of directory entries that can fit in one cluster, it is determined that all valid directory entries have been examined. As a result of the determination, if all the valid directory entries have not been examined, the process returns to step S602, and the processes after step S602 are performed for the directory specified in step S604. On the other hand, if all valid directory entries have been examined, the process proceeds to step S606.

In step S606, the new file creation processing unit 107 determines whether there is a valid directory entry that can be reused among the directory entries included in the directory to which the file specified by the application unit 104 belongs. To do. This determination is made based on whether or not the value of the flag 111 of the reuse directory entry information 108 is a value indicating validity. As a result of this determination, if there is a valid directory entry that can be reused (if the value of the flag 111 of the reuse directory entry information 108 is a value that indicates validity), the process proceeds to step S607; The process proceeds to step S609.
In step S607, the new file creation processing unit 107 records metadata for the new file in a valid directory entry that can be reused. The position of a valid directory entry that can be reused is determined based on the cluster number 109 and the offset 110 of the reuse directory entry information 108.
Next, in step S608, the new file creation processing unit 107 updates the flag 111 of the reuse directory entry information 108 to a value indicating use. And the process by the flowchart of FIG. 6 is complete | finished.

  On the other hand, when the process proceeds from step S606 to step S609, the new file creation processing unit 107 determines whether there is still a directory entry from which the file has been deleted. Here, if the value of the flag 111 of the reuse directory entry information 108 is a value indicating invalidity, the directory entry in which the file is deleted from the head of the directory is searched. If the value of the flag 111 of the reuse directory entry information 108 is a value indicating use, the directory entry from which the file has been deleted is searched from the directory entry position (offset 110) indicated by the reuse directory entry information 108. To do. If a directory entry in which a file has been deleted until the end of the directory is found, the process proceeds to step S610. If not, the process proceeds to step S611.

In step S610, the new file creation processing unit 107 records metadata for the new file in the directory entry determined to be found in step S609. In this case, the new file creation processing unit 107 stores the position (cluster number 109 and offset 110) where the directory entry being operated is recorded in the reuse directory entry information 108. In addition, the new file creation processing unit 107 updates the flag 111 of the reuse directory entry information 108 to a value indicating use. And the process by the flowchart of FIG. 6 is complete | finished.
On the other hand, when proceeding from step S609 to step S611, the new file creation processing unit 107 expands the cluster, and records metadata for the new file in the first directory entry of the expanded cluster. And the process by the flowchart of FIG. 6 is complete | finished.

As described above, in the present embodiment, when a new file is to be created in a certain directory, if there is no directory entry that has never been used, the following processing is performed. That is, the directory entry position information (cluster number 109 and offset 110) of the deleted file is used to search for a directory entry that can be reused, and the directory entry is reused. Therefore, a directory entry that can be reused can be found at high speed. If there is no directory entry that can be reused, the directory entry from which the file has been deleted is searched from the reused directory entry. As a result, when there is no directory entry for the deleted file in the directory in which the file is to be created, the operation of searching the entire directory can be omitted. Therefore, it is possible to shorten the time consumed for searching the position of the directory entry for a new file. As described above, in the present embodiment, the position of the directory entry for recording a newly created file can be searched at high speed.
In this embodiment, when a new file is created, if there are both an unused directory entry and a reusable directory entry in the same directory, the unused directory entry is preferentially used. I tried to do it. Therefore, it is possible to prevent the process of searching for a directory entry that can be reused from being performed more than necessary.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, a process for deleting the second and subsequent files when deleting two or more existing files in the same directory will be described. As described above, the present embodiment and the first embodiment are mainly different in part of the processing when deleting an existing file. Therefore, in the description of the present embodiment, the same portions as those in the first embodiment are denoted by the same reference numerals as those in FIGS.

FIG. 7 is a flowchart for explaining an example of processing of the file system apparatus when deleting an existing file. Since processes other than steps S704 to S705 in FIG. 7 are the same as those in the flowchart in FIG. 5 in the first embodiment, detailed description thereof will be omitted here.
In step S704, the file deletion processing unit 106 determines whether or not the value of the flag 111 of the reuse directory entry information 108 is a value indicating invalidity. As a result of this determination, if the value of the flag 111 is a value indicating invalidity, the process skips step S705 and proceeds to step S706. Otherwise, the process proceeds to step S705.

  In step S705, the file deletion processing unit 106 determines whether the directory entry position (cluster number 109 and offset 110) indicated by the reuse directory entry information 108 is behind the position of the directory entry being operated. Determine. As a result, if the position of the directory entry indicated by the reuse directory entry information 108 is behind the position of the directory entry being operated, the process proceeds to step S706. Otherwise, the process according to the flowchart of FIG. 7 is performed. finish.

  As described above, in the present embodiment, when there are two or more directory entries from which a file has been deleted in the same directory, reuse directory entry information is based on the directory entry closest to the head of the directory. 108 is created. Therefore, when a new file is created, a reusable directory entry can be searched at a higher speed when a reusable directory entry is searched from the top of the directory.

  In the description of the first and second embodiments described above, it is assumed that the FAT file system is used. However, the present invention is not limited to the FAT file system and may be applied to other file systems. Is possible.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

(Other examples)
The present invention is also realized by executing the following processing. That is, first, software (computer program) for realizing the functions of the above embodiments is supplied to a system or apparatus via a network or various storage media. Then, the computer (or CPU, MPU, etc.) of the system or apparatus reads and executes the computer program.

  101 CPU, 104 application section, 105 file system section

Claims (9)

A file management device that records a file in a directory and deletes a file recorded in the directory,
When the file is deleted, a set of information specifying the directory to which the deleted file belongs and information specifying the directory entry used by the deleted file is stored in the storage medium. Storage means;
Recording means for recording the new file in the directory entry specified by the information stored by the storage means when recording the new file in the directory to which the deleted file belonged. File management device.   If the same directory contains both a directory entry that has never been used and a directory entry from which a file has been deleted, the recording means will still use the new file. 2. The file management apparatus according to claim 1, wherein recording is preferentially performed on a directory entry that has not been recorded.   If there are two or more information specifying the directory entry used by the deleted file in the same directory, the storage means stores the information specifying the directory and the two or more directory entries. The file management apparatus according to claim 1 or 2, wherein a set of information to be specified and information specifying a directory entry closest to the head of the directory is stored in a storage medium. When the new file is recorded, the storage means includes a set of information specifying a directory to which the recorded new file belongs and information specifying a directory entry used by the recorded new file. In a storage medium,
The recording means includes a combination of information for specifying a directory to which the recorded new file belongs and information for specifying a directory entry used by the recorded new file in the storage medium. The file management apparatus according to any one of claims 1 to 3, wherein when the file is recorded, the directory entry for recording the next file is searched from the directory entry specified by the information. A file management method for recording a file in a directory and deleting a file recorded in the directory,
When the file is deleted, a set of information specifying the directory to which the deleted file belongs and information specifying the directory entry used by the deleted file is stored in the storage medium. Preservation process;
A recording step of recording the new file in the directory entry specified by the information stored in the storage step when the new file is recorded in the directory to which the deleted file belonged. File management method.   If the recording step includes both a directory entry that has never been used and a directory entry from which a file has been deleted, the new file is still used once. 6. The file management method according to claim 5, wherein recording is preferentially performed on a directory entry that has not been recorded.   If there are two or more information specifying the directory entry used by the deleted file in the same directory, the storing step includes information specifying the directory and the two or more directory entries. 7. The file management method according to claim 5, wherein a set of information specifying a directory entry closest to the head of the directory is stored in a storage medium. When the new file is recorded, the storing step includes a set of information specifying a directory to which the recorded new file belongs and information specifying a directory entry used by the recorded new file. In a storage medium,
In the recording step, a set of information specifying a directory to which the recorded new file belongs and information specifying a directory entry used by the recorded new file is stored in the storage medium. The file management method according to any one of claims 5 to 7, wherein when the file is recorded, the directory entry for recording the next file is searched from the directory entry specified by the information. A computer program for causing a computer to record a file in a directory and delete a file recorded in the directory,
When the file is deleted, a set of information specifying the directory to which the deleted file belongs and information specifying the directory entry used by the deleted file is stored in the storage medium. Preservation process;
When recording a new file in the directory to which the deleted file belonged, causing the computer to execute a recording step of recording the new file in the directory entry specified by the information stored in the storage step A computer program characterized by the above.

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