JP2002251310A - Method for preparing file system for flash memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the safety of data without risking a failure of rewriting an unchanged sector by reducing the number of times of rewriting sectors in updating a file system of a flash memory. SOLUTION: A sector area of the flash memory is made to correspond to an information storage block 21 and data storage blocks 22, 23 and 24 in the file system 20 of the flash memory. The file system 20 comprises a plurality of storage blocks being two kinds, which are the storage block 21 where file system information 20a, directory information 20b, file information 20c and path information 20d are arranged to be stored and the data storage blocks 22, 23 and 24 where data of each file of file data 20e is arranged to be stored. Only a corresponding sector is rewritten with respect to storage blocks of a changed file system to reduce the number of sector rewriting times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for creating a file system of a flash memory, and more particularly, to a method of rewriting a file system in a flash memory.

[0002]

2. Description of the Related Art Generally, in a file system,
For example, a secondary storage device such as a floppy (registered trademark) disk device or a hard disk device is used as a data storage area. As these secondary storage devices, those which can be randomly accessed in block units such as 512 bytes and 1024 bytes are generally used. On the other hand, in recent years, in the field of embedded software, a flash memory has been used instead of the above-described secondary storage device for a data storage area of a file system.

FIG. 9 is a diagram showing a configuration example of a file system of a flash memory. In FIG. 9, reference numeral 20 denotes a file system of a flash memory.
Indicates file system information 20a and directory information 2
0b, file information 20c, path information 20d, and file data 20e. By creating the file system shown in FIG. 9, writing the created image of the file system into the flash memory, and mounting it, the file and the tree structure can be mounted on the flash memory.

Here, rewriting of the flash memory is performed by
After erasing data in sector units, it becomes possible by writing data to the sector.

However, since the file system has a configuration in which the above five blocks are continuous, when the file system 20 on the flash memory is updated, the file system information 20 of the file system 20 is not updated.
a, the directory information 20b, the file information 20c, and the path information 20d are subjected to an information change and an expansion change of the storage size, and the start address of the file data 20e is also changed because the storage size is changed.

FIG. 10 shows a conventional file system 2.
FIG. 10A shows an example of the file system 20 before the update, and FIG.
(A) Update of data in file 3 and file 4
2 shows the file system 20 after the data has been deleted. In the conventional method shown in FIG. 10, updating the file system 20 on the flash memory requires rewriting the entire file system, that is, all the sectors corresponding to the size of the entire file system. However, this rewriting of the flash memory requires rewriting even the file data of a file that has not been changed, and thus cannot be said to be an appropriate rewriting method in a flash memory having a limited number of times of rewriting. In addition, rewriting of the entire file system, if the rewriting of the flash memory fails unexpectedly, causes the destruction of the file system itself. Therefore, it cannot be said that rewriting is appropriate in terms of data security.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and reduces unnecessary rewriting of sectors of a flash memory, and secures a file system on a flash memory and the security of unmodified file data. The purpose of this is to update the file system in consideration of the above.

[0008]

According to a first aspect of the present invention, in the flash memory file system creation method, a block considering a sector boundary in the file system of the flash memory is used as a storage block to store file system information, directory information, It is characterized by comprising two types and a plurality of storage blocks, an information storage block in which file information and path information are arranged to fit in a storage block, and a data storage block in which data for each file is arranged to fit in a storage block. It was done.

According to a second aspect of the present invention, in the first aspect of the present invention, the data for each file is arranged so as to fit in the data storage block in the chronological order of the update history of the file.

According to a third aspect of the present invention, in the first or second aspect, the information storage block of the file system information, the directory information, the file information, and the path information is single and the single block has an empty area. Data of a new update history for each file is arranged so as to fit in the information storage block.

[0011]

FIG. 1 is a diagram showing an example of the system configuration of an information processing apparatus for creating a file system 20 of a flash memory to which the present invention is applied.
U, 2 is RAM, 3 is ROM, 4 is a memory card interface, 5 is a memory card, 6 is a display unit,
7, an input unit; 8, an HDD; and 9, a system bus. The present system creates an image of the file system 20 to be written to the flash memory, and writes the image, a rewrite address and a size to the memory card 5 to write a rewrite program.

FIG. 2 is a diagram showing an example of a system configuration of an information processing apparatus for rewriting a file system 20 of a flash memory to which the present invention is applied. In the drawing, reference numeral 10 denotes a flash memory. When the information processing apparatus is started with the memory card 5 inserted, the system automatically executes the rewriting program on the memory card 5 and rewrites the file system 20 of the flash memory 10.

The file system 20 is composed of five blocks of file system information 20a, directory information 20b, file information 20c, path information 20d, and file data 20e. Each block has the following configuration.

1. File system information structrom_sblock {unsignedlong magic; Magic number for checking long time; File system creation date and time (1
Unsignedlong bsize; File system block size (4096) unsignedlong blocks; Data area blocks unsignedlong files; Total number of files unsignedlong nrdirent; Number of directory information unsignedlong nrnode; Number of file information unsignedlong pathsize; Total size of path information unsignedlong data_offset; Offset amount from start address to data area};

2. Directory information structrom_dirent {unsignedlong name; Offset value indicating where the character string of the file name is located in the path information unsignedlong rno; File number unsignedlong seq; Value indicating the order of files in the directory};

FIG. 3 shows an example of a directory structure. The directory information 20b is always continuously arranged by the number of files existing in the directory. The file order seq is allocated in descending order from the first entry of the directory, and becomes 0 in the last entry. In other words, seq is a value that indicates how many files remain in that directory. For example, when a certain file (filename) exists in a certain directory (directory), the structure is as shown in FIG.

3. File Information (Table of File Information) The files in the file system 20 have the following information for each file, and the file information is arranged in the order of the file numbers (rno). File information can be easily retrieved.

Structromfs_rnode {unsignedshort mode UNIX (registered trademark) file compatible mode information unsignedshort nlink Number of hard links to this file unsignedlong size File data size unsignedlong rno File number inside file system long ctime File creation date and time information (1970 / 01/0100:
Unsignedlong uid Owner's user number unsignedlong gid Group number unsignedlong offset File data location information (offset from the beginning of the file system data area. However, in the case of a directory, directory information Offset value within the)};

4. Path Information (Table of File Names) The path information 20d stores character strings of all file names existing in the file system, and all character strings are terminated with NULL (== 0x00). As shown in FIG. 3, the character string of each file name is specified by the name pointer of the directory information 20b corresponding to the file.
In the case of a symbolic link file, the file name of the symbolic link destination is stored in the area of the path information 20d to which the data_offset pointer of the file information 20c points.

[5] File Data Data of all files in the file system 20 is stored in block units. That is, no matter how small a file, for example, a file of only one byte, the data area of the file system 20 has one block (409 bytes).
6 bytes).

FIG. 4 is a diagram showing an example of the configuration of a file system 20 in consideration of sector boundaries of a flash memory to which the present invention is applied. FIG. 4A shows a file system of a flash memory, and FIG. () Shows the sector configuration of the flash memory. As shown in FIG. 4A, the file system 20 mainly includes an information storage block 21, which is an area for mainly storing information, and data storage blocks 22, 23, 24, which are areas for storing data. Data arrangement is performed on 20 blocks in consideration of the sector boundaries of the flash memory.

Here, the sector area of the flash memory shown in FIG. 4B is used as a storage block in the file system. First, file system information 20a, directory information 20b, file information 20c, and path information 20d.
The four are arranged so as to fit in the information storage block 21, and the unwritten area is set as an empty area in consideration of the expansion of each information due to future file system update as an information spare area 20f. Next, the file data 20e is arranged such that the data for each file from the top of the data storage blocks 22, 23, and 24 fits in each data storage block, and the area where the data of the file is not arranged is an unused area. Become.

FIG. 5 is a flowchart illustrating an example of a rewriting process of the file system 20 of the flash memory to which the present invention is applied. It is assumed that the sector number of the flash memory is s, the storage block number of the file system 20 of the flash memory to be written is b, and the common offset value of these two is o. First, the sector number s of the flash memory and the storage block number b of the file system 20 of the flash memory to be written are set to 0 (step S1), and the common offset value o is set to 0 (step S2). The data values at the offset value o from each head address are sequentially compared (step S3). Here, if there is a data difference (NO), the s-th sector as the target is erased (step S8), and the offset value o is set to 0 (step S9). Then, rewriting is performed in the storage block of the file system 20 to be rewritten (step S10), and the process moves to the next sector (step S11), and it is determined whether or not the offset value o is larger than the sector (storage block) size. (Step S1
2) If the size is larger (in the case of YES), the process proceeds to the next storage block and sector of the rewrite file system (step S6).

If there is no difference in step S3 (in the case of YES), the process moves to the next sector (step S3).
4) It is determined whether or not the offset value o is larger than the sector (storage block) size (step S5). If it is larger (YES), the process moves to the next storage block and sector of the rewrite file system in step S6, and the same processing is performed. I do. This process is executed as long as there is a storage block of the rewrite file system or as long as there is a sector of the flash memory (step S7).

FIG. 6 is a diagram showing an example of a rewriting process of the file system 20 of the flash memory.
6A shows a data storage block, FIG. 6A shows a file system to be rewritten, and FIG. 6B shows a file system written in a flash memory. FIG.
A file system 20 to be rewritten as shown in FIG.
In FIG. 6B, the data of the file 2 in the file data 20e is updated, the data size of the file 2 is reduced, and the data of the file 2 can be accommodated in the data storage block 22, and as shown in FIG. The whole system has to be rewritten.

FIG. 7 is a diagram showing an example of a rewriting process of the file system 20 of the flash memory.
FIG. 7 shows a file system to be rewritten in FIG.
FIG. 6B shows a file system written in the flash memory. The configuration of the file system 20 of the flash memory is further examined with respect to the example shown in FIG. In the example shown in FIG. 7B, in the file data in the file system 20 of the flash memory, data is arranged from the oldest file data to the data storage block based on the update history of the file. Here, file 3, file 5,
Arranged in file 2, file 1, file 4.

In the method of creating the file system 20 shown in FIG. 7, a file having an old update history is unlikely to be changed in the future, and a new file is likely to be frequently changed. Of the file system 20 in the file system 20 to be rewritten as shown in FIG.
By setting the displacement of e at the end of the data storage block, the number of sectors requiring rewriting can be reduced. At this time, similarly to the example shown in FIG. 6, when only the data of the file 2 is updated and the data size is reduced, in the example shown in FIG. This eliminates the need to rewrite the sector, thereby reducing the number of times the sector is rewritten.

FIG. 8 is a diagram showing an example of a rewriting process of the file system 20 of the flash memory.
FIG. 8 shows a file system to be rewritten in FIG.
(B) shows a file system written in the flash memory. In the example shown in FIG. 8B, in order to reduce the number of times of rewriting of the sector, when the number of information storage blocks 21 is one, data is stored as long as the latest file can be sequentially stored in the information spare area 20f of the information storage block 21. I do.
File system 20 on flash memory to be rewritten
Then, every time you change the file, the file information changes. That is, in rewriting the file system 20, the sector corresponding to the information storage block 21 must be rewritten without fail.

Here, if the changed file has a data size that can be accommodated in the information spare area 20f, rewriting of the data storage block 22 and subsequent data constituting the file data becomes unnecessary, and furthermore, rewriting of sectors can be reduced. it can. In the example shown in FIG.
For the data change, only the first sector needs to be rewritten.

[0030]

According to the first aspect of the present invention, when rewriting a file system, only when the configuration of the data storage block is not changed when the file system is created, the changed storage block of the file system is deleted. Sector rewriting can be performed, the number of times of sector rewriting can be reduced, and the security of data can be ensured because there is no risk of rewriting failure for unmodified sectors.

According to the second aspect of the present invention, the file data is arranged in the data storage block in ascending order of the possibility of file change, so that the configuration change of the data storage block is at the end of the file data. The number of times of sector rewriting can be reduced as compared with the first invention, and data security can be ensured because there is no need to expose the unmodified sector to the risk of rewriting failure.

According to the third aspect of the present invention, when the changed file fits in the free area of the information storage block,
Sector rewriting can be performed only for the information storage block of the file system information, directory information, file information, and path information for which sector rewriting is always performed. Data security can be ensured because there is no need to risk rewriting failure for an empty sector.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a system configuration of an information processing apparatus that creates a file system of a flash memory to which the present invention is applied.

FIG. 2 is a diagram illustrating an example of a system configuration of an information processing apparatus that rewrites a file system of a flash memory to which the present invention is applied.

FIG. 3 is a diagram illustrating an example of a directory structure.

FIG. 4 is a diagram showing a configuration example of a file system in which a sector boundary of a flash memory to which the present invention is applied is considered.

FIG. 5 is a flowchart illustrating an example of a rewriting process of a file system of a flash memory to which the present invention is applied.

FIG. 6 is a diagram illustrating an example of a rewriting process of a file system of a flash memory.

FIG. 7 is a diagram illustrating an example of a rewriting process of a file system of a flash memory.

FIG. 8 is a diagram showing an example of a rewriting process of a file system of a flash memory.

FIG. 9 is a diagram illustrating a configuration example of a file system of a flash memory.

FIG. 10 is a diagram illustrating an example of updating a conventional file system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... RAM, 3 ... ROM, 4 ... Memory card interface, 5 ... Memory card, 6 ... Display part, 7
... Input unit, 8 HDD, 9 system bus, 10 flash memory, 20 file system, 20a file system information, 20b directory information, 20c
... file information, 20d ... path information, 20e ... file data, 20f ... information spare area, 21, information storage block, 22, 23, 24, 25 ... data storage block.

Claims (3)

[Claims] In a method for creating a file system of a flash memory, a block considering a sector boundary in a file system of a flash memory is set as a storage block, and file system information, directory information, file information, and path information are stored in the storage block. A file system creation method for a flash memory, comprising two types and a plurality of storage blocks, an information storage block arranged in a storage block and data storage blocks arranged so that data for each file fits in the storage block. 2. A flash memory file system according to claim 1, wherein data of each file is arranged in a data storage block in the order of older file update history. System creation method. 3. The file system creation method for a flash memory according to claim 1, wherein a single information storage block for file system information, directory information, file information, and path information is provided, and a free area of the single block. A file system creation method for a flash memory, wherein data for each new file in the update history is arranged so as to fit in the information storage block.