Method for arranging items of directory in file system
A file system and directory item technology, applied in the direction of electrical digital data processing, special data processing applications, instruments, etc., can solve problems such as failure to meet customer needs, time-consuming, resource waste, etc., to reduce the number of directory items and improve operational efficiency , the effect of improving the utilization rate
Inactive Publication Date: 2008-07-23
VIMICRO CORP
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Problems solved by technology
When searching or creating a file or directory, it is necessary to compare the name of the target file or directory with each directory item in the directory area. Since the directory items are stored continuously, the comparison is to compare in order according to the physical address, so it will also be compared. Compared with deleted directory entries, if there are many deleted directory entries, there will be more useless search operations, resulting in more waste of resources
For example: in an external storage device file system in an embedded system, in a directory whose number of useful directory entries is 100 and the number of deleted directory entries is 0, the time to create a new file is about 150 milliseconds; but in a The number of useful directory entries is 100, and the number of deleted directory entries is 6000. The time to create a new file is about 1400 milliseconds, and the time spent is about 10 times different. The time wasted on deleted directory entries takes up 90% of the system. resource
[0010] The resources and performance of the embedded system are relatively limited. In this case, it will be very time-consuming to perform file operations such as creating, deleting, and searching, which will lead to a decline in the overall performance of the product and cannot meet customer needs.
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[0031] The technical solution of the present invention will be described in more detail below with reference to the drawings and embodiments.
[0032] For the convenience of the following description, the following briefly introduces the structure of the directory area, such as figure 1 shown. A directory area occupies one or more clusters. The physical addresses of these clusters are not necessarily continuous. The relationship and sequence between clusters are determined according to the cluster chain of the directory area in the FAT table. For example, the directory area occupies 3 clusters in total. : 1, 2 and 3; the next cluster of 1 in the chain is 2, that is, the linked list pointer of 1 points to 2; the next cluster of 2 is 3, that is, the linked list pointer of 2 points to 3.
[0033] The cluster number of the root directory is recorded in the BIOS parameter block. The first cluster number of the subdirectory is recorded in the FDT of the upper directory of the subd...
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A method for arranging catalogue item of file system includes confirming object catalogue and checking catalogue item, judging whether each catalogue item in object catalogue is effective catalogue item or deleted catalogue item, moving found-deleted catalogue item into a cluster when found-deleted catalogue items are enough to be packed in a cluster, setting first byte of all catalogue items in cluster to be zero when movement is finished and deleting said cluster off from cluster chain of object catalogue.
Description
technical field [0001] The invention relates to a file system, in particular to directory item arrangement of the file system. Background technique [0002] Now many embedded handheld devices such as mobile phones, MP3 / MP4 players, etc. begin to support external memory interfaces, such as SD card standard interface, NandFlash interface and so on. These embedded handheld devices all use the FAT (file allocation table) file system as the interface to access the external memory, and use the FAT12 / FAT16 / FAT32 file system to perform file reading and writing operations according to the capacity of the external memory. [0003] The file system on the non-volatile memory generally has a BIOS (basic input and output system) parameter block, a file allocation table (FAT table), a root directory, and a data area. Such a file system is generally called a FAT file system, and currently includes FAT12, There are three types of FAT16 and FAT32, and clusters are used as the basic storage u...
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IPC IPC(8): G06F17/30
Inventor 高占东蒋长洪
Owner VIMICRO CORP