Access device, information recording device, information recording system, file management method, and program

Abstract

An information recording device, which includes a nonvolatile memory whose areas are managed using an FAT file system and enhances the reliability of directory entries using a cyclic shift checksum, recalculates the cyclic shift checksum efficiently and performs seeking at a higher speed. A nonvolatile memory ( 25 ) of an information recording device 2 is managed using an FAT file system. In the memory, a plurality of directory entries are allocated to a single file. The device enhances the reliability of the directory entries using a cyclic shift checksum, and manages information indicating the position and the size of a storage area of file data using an extent information entry ( 203 ). The device further uses an update information entry ( 204 ) and a dummy entry ( 205 ).

1 . An access device that accesses an information recording device including a nonvolatile memory storing file data, the access device comprising:
 a file system control unit that manages a file using an extent information entry, a file allocation table, and an entry group,   the extent information entry managing the file data in units of fixed-length blocks and including, as management information for a continuous area including one or more fixed-length blocks, information for identifying at least a position and a size of the continuous area,   the file allocation table managing information indicating a link between the fixed-length blocks, and   the entry group being generated for each file, and internally including one or more fixed-length entries storing management information including information about a name and a size of the file and information about a checksum of the one or more fixed-length entries,   wherein the file system control unit stores the extent information entry into an external area consisted of the fixed-length blocks, each of which has a predetermined length, the external area being external to the area of the entry group.   
     
     
         2 . The access device according to  claim 1 , wherein
 the entry group includes an extent area designation entry including information for identifying a position and a size of the extent area.   
     
     
         3 . The access device according to  claim 2 , wherein
 the file system control unit adds an extent area extent information entry including information for identifying a position and a size of a continuous area every time when an independent continuous area storing data of the file increases.   
     
     
         4 . The access device according to  claim 3 , wherein
 a byte length of the extent area extent information entry is identical to a byte length of an entry included in the entry group.   
     
     
         5 . The access device according to  claim 3 , wherein
 a byte length of the extent area extent information entry is different from a byte length of an entry included in the entry group.   
     
     
         6 . The access device according to  claim 1 , wherein
 the information about the checksum includes a calculation result of a cyclic shift checksum.   
     
     
         7 . The access device according to  claim 1 , wherein
 the file system control unit includes   an extensible file processing unit that, when accessing a file, controls access to the file based on the extent area designation entry and the extent area extent information entry when the entry group corresponding to the file includes the extent area designation entry, and   a normal file processing unit that, when accessing a file, controls access to the file based on the file allocation table when the entry group corresponding to the file includes no extent area designation entry.   
     
     
         8 . An information recording device including a nonvolatile memory storing file data, wherein
 the file data is managed in units of fixed-length blocks, and   the nonvolatile memory stores an extent information entry, a file allocation table, and an entry group, the extent information entry including, as management information for a continuous area including one or more fixed-length blocks, information for identifying at least a position and a size of the continuous area, the file allocation table managing information indicating a link between the fixed-length blocks, and the entry group being generated for a single file and internally including one or more fixed-length entries storing management information including information about a name and a size of the file and information about a checksum of the one or more fixed-length entries, and   the extent information entry is stored into an area that is external to the entry group and is included in an extent area formed by a fixed-length block.   
     
     
         9 . The information recording device according to  claim 8 , wherein
 the entry group includes an extent area designation entry including information for identifying a position and a size of the extent area.   
     
     
         10 . The information recording device according to  claim 9 , wherein
 an extent area extent information entry including information for identifying a position and a size of a continuous area is added to the extent area every time when an independent continuous area storing data of the file increases.   
     
     
         11 . The information recording device according to  claim 10 , wherein
 a byte length of the extent area extent information entry is identical to a byte length of an entry included in the entry group.   
     
     
         12 . The information recording device according to  claim 10 , wherein
 a byte length of the extent area extent information entry is different from a byte length of an entry included in the entry group.   
     
     
         13 . The information recording device according to  claim 8 , wherein
 the information about the checksum includes a calculation result of a cyclic shift checksum.   
     
     
         14 . An information recording system including an information recording device including a nonvolatile memory storing file data and an access device that accesses the information recording device, wherein
 the file data is managed in units of fixed-length blocks, and   the nonvolatile memory stores an extent information entry, a file allocation table, and an entry group, the extent information entry including, as management information for a continuous area including one or more fixed-length blocks, information for identifying at least a position and a size of the continuous area, the file allocation table managing information indicating a link between the fixed-length blocks, and the entry group being generated for a single file and internally including one or more fixed-length entries storing management information including information about a name and a size of the file and information about a checksum of the one or more fixed-length entries,   the access device includes a file system control unit that manages a file stored in the nonvolatile memory using information stored in the nonvolatile memory, and   the extent information entry is stored into an area that is external to the entry group and is included in an extent area formed by a fixed-length block.   
     
     
         15 . An information recording system, comprising:
 the access device according to  claim 1 ; and   an information recording device including a nonvolatile memory storing file data, wherein   the file data is managed in units of fixed-length blocks, and   the nonvolatile memory stores an extent information entry, a file allocation table, and an entry group, the extent information entry including, as management information for a continuous area including one or more fixed-length blocks, information for identifying at least a position and a size of the continuous area, the file allocation table managing information indicating a link between the fixed-length blocks, and the entry group being generated for a single file and internally including one or more fixed-length entries storing management information including information about a name and a size of the file and information about a checksum of the one or more fixed-length entries, and   the extent information entry is stored into an area that is external to the entry group and is included in an extent area formed by a fixed-length block.   
     
     
         16 . A file management method using a nonvolatile memory storing file data, the method comprising:
 managing a file using an extent information entry, a file allocation table, and an entry group, the extent information entry managing the file data in units of fixed-length blocks and including, as management information for a continuous area including one or more fixed-length blocks, information for identifying at least a position and a size of the continuous area, the file allocation table managing information indicating a link between the fixed-length blocks, and the entry group being generated for a single file and internally including one or more fixed-length entries storing management information including information about a name and a size of the file and information about a checksum of the one or more fixed-length entries,   wherein the extent information entry is stored into an area that is external to the entry group and is included in an extent area formed by a fixed-length block.   
     
     
         17 . A computer-readable storage medium storing a program enabling a computer to implement the file management method according to  claim 16 .