JP2007080240A - Technique for accessing file allocation table - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To disclose techniques for accessing a file allocation table (FAT). <P>SOLUTION: According to one aspect of the present invention, after the FAT from an external storage device is obtained in an interface, a linked list of clusters assigned to a file in the external storage device is distilled. The contiguous ranges of clusters in the linked list of clusters are compressed into packed records, each including location information of a first cluster and length information of a contiguous range of clusters; and the packed records are stored into a random access memory in order. By relying on the interface to manage access to the FAT in the external storage device, a processor in the device sends only an access request and then is released to perform other tasks while accessing the FAT. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to data processing, and more particularly, to an apparatus and method for managing a file allocation table more efficiently.

  The FAT file system is well-known and is described in several documents, including IBM DISK OPERATING SYSTEM TECHNICAL REFERENCE published by AD 1988, the contents of which are incorporated herein by reference. . Simply put, the FAT file system divides the disk into clusters of 512 byte sectors. Files are stored in one or more clusters according to file length. The disk further includes a boot record, a file allocation table (FAT), a root directory, and a data area including subdirectories and files. A directory is a tree-structured directory system. A particular file is searched by specifying the drive on which it resides, the directory path, and the file name, eg, c: /dir1/dir2/filename.ext.

  FIG. 1 is a block diagram of a FAT file system disk format. The FAT file system is briefly explained next. The FAT file system revolves around a FAT allocation table (FAT). Each logical volume is associated with its own FAT, which is created or expanded to include allocation information for each file on the volume in the form of a linked list of allocation devices, namely in the form of a linked list of allocation devices. Indicates an allocation cluster that is in a free state for allocation to a file. If the disk is formatted by the FAT file system, the boot sector is written to sector 0. This is followed by one or more file allocation tables. Each file allocation table is physically located on one or more definable FAT storage devices of the formatted disk. A definable FAT storage device is usually a 512 byte sector on an external disk storage device, but the capacity of the FAT storage device may be above or below 512 bytes, such as 256 bytes or 1024 bytes. . The file allocation table is followed by the root directory. The root directory is followed by a volume file. The boot sector includes various description information such as a volume, a drive number and a volume ID, the number of sectors per FAT, and a bootstrap routine in an area represented as a boot parameter block, that is, BPB.

  The file allocation table is divided into fields directly corresponding to allocatable clusters on the disk. The first two FAT entries are reserved and the remaining FAT entries describe the use of the corresponding disk cluster. Each file entry in the root directory contains the number of the first cluster assigned to that file, which is used as an entry point into the FAT. From that entry point forward, each FAT field contains the number of the next cluster in the file until the end-of-cluster mark is reached. FIG. 2 shows an example of a file allocation table portion specifically showing a linked list of clusters allocated to the file.

  FAT systems are not only used in personal computers and notebook computers, but also in certain relatively small consumer electronics such as digital music players and cameras, personal digital assistants (PDAs), video cameras, mobile phones, etc. It is also used in products. Generally, when accessing a file stored on a hard disk, a memory card, or an external mechanism device, the FAT must first be read into a ROM of a computer or a buffer storage device of a consumer electronic product. Based on the FAT information, the central processing unit (CPU) sends an appropriate access command to the storage device to access a desired file stored on the external storage device.

  The FAT can be of a small enough capacity to always be secured in a commonly used personal computer (PC) or notebook computer. However, FAT can be too large for constant storage in the buffer storage of some relatively small consumer electronic products (eg, PDAs), thus Reduce system performance and data throughput. In any case, the central processing unit in the device, whether it is a PC, notebook or consumer electronic product, directly manages the FAT, thereby occupying and performing some resources of the CPU In addition, it degrades the performance of other tasks that require CPU resources.

  Therefore, there is a need for a technique for accessing the file allocation table more efficiently with minimal impact on CPU resources.

  This part is for the purpose of summarizing some features of the present invention and is intended to briefly introduce some of the preferred embodiments. Simplifications or omissions in this part of the specification, abstracts, or names of the present invention may be made so as not to obscure the purpose of the part, abstract or name. Such simplifications and omissions are not intended to limit the scope of the invention.

  In general, the present invention relates to a technique for accessing a file allocation table (FAT). According to one aspect of the present invention, after a FAT is obtained from an external storage device at the interface, a linked list of clusters assigned to files in the external storage device is extracted. The adjacent areas of the cluster in the linked list of clusters are compressed into pack records, each including position information of the first cluster and length information of the adjacent areas of the cluster, and the pack record includes random access memory Are stored in order. By relying on the interface managing access to the FAT in the external storage device, the processor in the device is only sent access requests and is freed to perform other tasks while accessing the FAT.

  The present invention can be implemented as a system, apparatus, or method in hardware and software. According to one embodiment, the method of the present application is a method of accessing a file allocation table (FAT) comprising: obtaining a FAT from an external storage device; and linking a cluster assigned to a file in the external storage device. Extracting a list; and compressing adjacent areas of clusters in a linked list of clusters into packed records, each of which includes position information of a first cluster and length information of adjacent areas of the cluster. And storing the pack records in the random access memory in order.

  According to one embodiment, the device of the present application is a device that accesses a file allocation table (FAT), which obtains the FAT from an external storage device and allocates the link of the cluster assigned to the file in the external storage device. A FAT access device for extracting the list, and a compression device for compressing the adjacent region of the cluster in the linked list of the cluster into a pack record, each of which includes position information of the first cluster and the length of the adjacent region of the cluster And a result storage device for sequentially storing the pack records in the random access memory.

  One of the objects, features, and effects of the present invention is to provide an efficient method for accessing a file allocation table.

  Other objects, features and advantages of the present invention will become apparent from the following detailed description of an embodiment thereof, considered in conjunction with the accompanying drawings.

  These and other features, aspects and advantages of the present invention will become more apparent with respect to the following description, appended claims and accompanying drawings.

  The detailed description of the present invention is generally presented in terms of procedures, steps, logic blocks, processes and other symbolic representations that are directly or indirectly similar to the operation of the apparatus or system envisaged in the present invention. Such descriptions and expressions are commonly used by those skilled in the art to most effectively convey the essence of their work to others skilled in the art.

  References to “one embodiment” or “an embodiment” in the present specification and claims include that the particular feature, structure, or characteristic described with respect to the embodiment can be included in at least one embodiment of the invention. Means that. The occurrences of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, but are independent of or separate from other embodiments. Nor does it represent an example. Further, the order of blocks or the use of sequential numbers in a process flowchart or process diagram, which represents one or more embodiments of the invention, may be used in the present invention to indicate any particular order. It does not suggest any constraints.

  In the prior art, the FAT has a relatively large capacity to be always held in the buffer storage space of a device, particularly a portable device such as a mobile phone or a PDA. To access the FAT, the FAT must be paged separately into the buffer storage under the control of the device's processor, thus reducing the system performance and data throughput of the device itself. However, it can be seen that there are many adjacent regions of the cluster that occupy a large volume of limited buffer storage allocated to the file. For example, referring to FIG. 3, the cluster numbers assigned to the files are a, a + 1, a + 2, a + 3, b, b + 1, b + 2, b + 3, c + 1, c + 2, c + 3, c + 4, and d, and a, b, c, and d represent different natural numbers. According to one aspect of the present invention, FAT is compressed in a random access memory to improve access efficiency without burdening the computational load on the processor. In another aspect of the invention, an acceleration device is provided as an interface between the external storage device and the device (or its processor). The acceleration device is configured to manage access operations so that the processor is freed to perform other tasks.

  Referring now to FIG. 5, at 501, a FAT is obtained from the external storage device, and a linked list of clusters assigned to the file is extracted from the FAT. The linked list of clusters assigned to the file shown in Figure 3 is a, a + 1, a + 2, a + 3, b, b + 1, b + 2, b + 3, c + 1, c + 2 , C + 3, c + 4, d. At 502, the adjacent region of the cluster in the cluster linked list is compressed into a pack record containing its location information and length information. The position information includes, for example, a cluster number called the first cluster. For example, referring to FIG. 4B, since the first adjacent region of the cluster is indicated as a, a + 1, a + 2, a + 3, the first pack record is the position of the first cluster. Includes a as information and 4 as length information.

  In 502, if there is another adjacent area of the cluster, it can be compressed into a pack record. At 503, packed records are stored in the random access memory in the order in which the adjacent areas of the cluster are placed in the linked list of clusters instead of the linked list of clusters. At 504, the file is accessed by the host processor via a pack record rather than a cluster linked list. In the illustrated embodiment, the cluster linked list pack format takes advantage of the adjacent region characteristics of the cluster to reduce the volume of the cluster linked list.

  Referring to FIG. 6, the FAT access device includes a FAT access device 601 that can be directly accessed by the host processor, a compression device 602, and a result storage device 603. The FAT access device 601 is configured to access the FAT stored in the external storage device 600 and extract a linked list of clusters assigned to the file. An example of a FAT access device 601 is shown in FIG. 7, which will be described in detail in the following paragraphs. The compression device 602 is configured to compress the linked list of clusters into packed records. Result storage device 603 is configured to store pack records. Thus, the host processor can access files on the external storage device by packed records rather than by a linked list of clusters.

The compression processing at 502 performed by the compression device 602 is as follows:
The first cluster number of the cluster link list such as a in FIG. 3 is obtained from the FAT access device 601 as the position information of the first cluster in the adjacent area of the cluster, and the value of the LENGTH information in the adjacent area of the cluster Setting 1 to 1,
Obtaining a next cluster number from the FAT access device 601 and determining whether the first cluster number is adjacent to the next cluster number;
If the determination result is affirmative, the value of LENGTH information is incremented by 1 and the last step is repeated. If the determination result is negative, the next cluster is used as the position information of the first cluster in the adjacent area of the next cluster Setting a number and repeating the above steps until the end information is reached.

  An example of a FAT access device 601 having a communication interface between the external storage device and the host processor of the device is shown in FIG. By placing FAT management on the accelerated device 300, the host processor is freed to perform other tasks that need to be done when the external storage device is being accessed.

  In one embodiment, the FAT access device 601 includes a central control unit (CCU) 301, a FAT storage sector calculation device (FAT storage sector CU) 302, a FAT storage sector access device (FAT storage sector AU) 303, a buffer 304, data A pre-access device 305 and a result storage device 306 are provided. Note that the FAT access device 601 may be incorporated in an external storage device, or may be integrated on a single chip together with a host processor (not shown), and from the external storage device and the host processor in the physical structure. It may be separated. The buffer 304 typically has a 512-byte volume, but may have any predetermined capacity, such as 1024 bytes or 2048 bytes.

  When the host processor makes a read access request to read a file in the external storage device, the start cluster number included in the root directory of the external storage device and assigned to the object file is assigned to the acceleration device 300. Sent. Referring now to FIG. 8, which is preferably understood in conjunction with FIG. 7, at 801, the CCU 301 obtains the starting cluster number of the object file and sends it to the FAT storage sector CU302. In 802, the FAT storage sector CU302 calculates the number of the FAT storage sector in which the start cluster number is stored, and sends the calculation result to the FAT storage sector AU303. In the illustrated embodiment, the calculation of the FAT storage sector CU302 is

の式を参照し、LBAはFATの一部が記憶されているFAT記憶セクタの番号を表し、FAT_start
は、FAT記憶セクタの開始番号を表し、Indexはクラスタ・インデックス番号を表し、開始クラスタ番号は、第１のクラスタ・インデックス番号としての役目を担い、Size_sectorは、512バイト、1024バイト、2048バイト、4096バイトなどの各FAT記憶セクタのボリュームを表し、Len_unitは、各クラスタ番号によって占められるボリュームを表す。FAT12、FAT16及びFAT32における各クラスタ番号は、3バイトと、4バイトと、8バイトとの各々を占める。

LBA represents the number of the FAT storage sector in which a part of the FAT is stored, and FAT _start
Represents the start number of the FAT storage sector, Index represents the cluster index number, the start cluster number serves as the first cluster index number, and the Size _sector is 512 bytes, 1024 bytes, 2048 bytes , 4096 bytes, etc., each FAT storage sector volume, Len _unit represents the volume occupied by each cluster number. Each cluster number in FAT12, FAT16, and FAT32 occupies 3 bytes, 4 bytes, and 8 bytes.

  In 803, the FAT storage sector AU303 reads a part of the FAT in the FAT storage sector determined in 802, and sends a part of the FAT to the buffer 304. In 604, the pre-access device 305 reads the content included in the starting cluster number that is considered as the first cluster index number. In 805, the CCU 301 reads the content included in the start cluster number and stores it in the result storage device 306. In 806, the CCU 301 sends the content included in the start cluster number to the FAT storage sector CU303 as the next cluster index number, and repeats the above steps until the end cluster mark is reached. When the end cluster mark is reached in 806, the entity link list of the cluster assigned to the object file is collected in the result storage device 306, and the read access procedure of the FAT access device 601 is completed.

  One important feature of the present invention is that the entire FAT is not sent to the host processor before an access request is made, but instead the host processor is freed to perform other tasks. Sometimes FAT is managed by an accelerated device. Other features, benefits and advantages can be seen from the above detailed description of the invention.

  The present invention has been described in sufficient detail with a certain degree of specificity. The disclosure of the embodiments of the present application is merely an example, and various changes in arrangement and combination of parts can be exercised without departing from the spirit and scope of the present invention described in the claims. Will be understood by those skilled in the art. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of the embodiments.

It is a figure which shows the disk format of a FAT file system. FIG. 4 is a diagram showing an example of a file allocation table fragment specifically showing a linked list of clusters allocated to a file. It is a figure which shows another example of the link list | wrist of the cluster allocated to a file. FIG. 4 is a diagram showing a packet format of a link list of the cluster shown in FIG. It is a figure which shows the packing method which compresses the link list of a cluster of FAT. It is a figure which shows the pack apparatus which compresses the link list of a cluster of FAT. FIG. 3 is a block diagram schematically showing a FAT access device that obtains a linked list of clusters from an external storage device. 5 is a flowchart showing an operation procedure of a read access of a FAT access device to a FAT in an external storage device.

Explanation of symbols

300 Accelerator
301 Central control unit
302 FAT storage sector calculation device
303 FAT storage sector access device
304 buffers
305 Advance access device
306 Result storage device
307 result storage
310 External storage
3011 reading subunit
3012 Newly created subunit
3013 Revised subunit
3014 Deletion subunit
600 External storage device
601 FAT access device
602 compressor
603 result storage

Claims (9)

A method for accessing a file allocation table (FAT),
Obtaining the FAT from an external storage device;
Extracting a linked list of clusters assigned to files in the external storage device;
Compressing adjacent areas of clusters in the linked list of clusters into packed records,
Each of the pack records includes position information of the first cluster and length information of adjacent areas of the cluster,
The method further comprises the step of sequentially storing the pack records in a random access memory. The method of claim 1, wherein
The step of obtaining the FAT is performed by an access device including an interface between the external storage device and a processor in the device accessing the external storage device,
The access device comprises a central controller, a FAT storage sector calculation device, a FAT storage sector access device, a buffer, and a result storage device. The method of claim 2, comprising
The step of obtaining the FAT includes
Obtaining a starting cluster number to which an object file from a host processor is assigned and sending the starting cluster number to the FAT storage sector calculation device as a first cluster index number by the central controller;
Calculating a FAT storage sector number corresponding to the first cluster index number by the FAT storage sector calculating device;
The FAT storage sector access device reads the part of the FAT into the buffer according to the calculation result;
Reading the contents of the first cluster index number by the central controller;
The content of the first cluster index number is stored by the central controller in the result storage device to obtain a linked list of clusters assigned to the object file, and the first cluster Sending the content of the index number to the FAT storage sector calculation device as a next cluster index number, and repeating the corresponding steps until reaching the end cluster mark of the object file, how to. The method of claim 1, wherein
The number of the first cluster is set as the position information of the first cluster. The method of claim 1, wherein
Compressing adjacent regions of the cluster,
Obtaining a first cluster number of the cluster link list as position information of the first cluster in the adjacent area of the cluster, and setting a value of LENGTH information of the adjacent area of the cluster to 1,
Obtaining a next cluster number and determining whether the first cluster number is adjacent to the next cluster number;
When the first cluster number is adjacent to the next cluster number, the step of increasing the value of the LENGTH information by 1, or when the first cluster number is not adjacent to the next cluster number And setting the next cluster number as the position information of the first cluster in the next adjacent region of the cluster. The method of claim 1, wherein
A method wherein a host processor can access the file by the packed record instead of the linked list of clusters. The method of claim 6, wherein
The location information of the first cluster and the length information of a number of adjacent areas of the cluster are stored in a result storage device that can be accessed directly by the host processor. A device that accesses FAT,
A FAT access device that obtains the FAT from an external storage device and extracts a linked list of clusters assigned to files in the external storage device;
A compression device that compresses adjacent areas of clusters in the linked list of clusters into packed records;
Each of the pack records includes position information of the first cluster and length information of adjacent areas of the cluster,
The apparatus further comprises a result storage device for sequentially storing the pack records in a random access memory. The device of claim 8, wherein
The access device having a communication interface between the external storage device and a host processor of the device includes a central control device, a FAT storage sector calculation device, a FAT storage sector access device, a buffer, and a result storage device. A device comprising:

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