CN102184213B - Method for reducing time and space overhead of creating FAT (File Allocation Table) filename by embedded equipment - Google Patents
Method for reducing time and space overhead of creating FAT (File Allocation Table) filename by embedded equipment Download PDFInfo
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Abstract
The invention provides a method for reducing time and space overhead of creating an FAT (File Allocation Table) filename by embedded equipment. A bitmap is defined in a memory of the embedded equipment, operates of determining to pre-create an expansion sequence number of a short catalog corresponding to the filename, determining whether files with same names exist and determining positions of storing the files are carried out synchronously, thus time and space of creating the FAT filename on the embedded equipment are greatly saved.
Description
[technical field]
The present invention relates to a kind of field of embedded technology, relate in particular to a kind of method that embedded device is created FAT filename time and space expense that reduces.
[background technology]
Early stage DOS names with 8.3 formatted file naming methods, and the demand file important name can not surpass 8 characters, extension name and can not surpass 3 characters, and not support Chinese character.The development of Along with computer technology, the file number of recorded information is with explosive growth.8.3 the short filename form far can not satisfy the requirement of people to file designation.For this reason, the FAT32 file system of Windows has realized long filenames mechanism.The principle of FAT file system can be described as a storage space piecemeal simply and be mapped in the table, thereby realizes the flexible domination to storage space.Each piece in the storage space is called as bunch, and the mapping table of storage space is known as the FAT table.
Introduce of the management of FAT32 file system below to file.
Describe as file except all corresponding one group of data of All Files (sub-directory also exists as a kind of special file) of root directory, be called as filename.Each filename is made up of one or more file directory item, and each file directory item is made up of 32 bytes (byte has 8 bits).So-called 8.3 form short filenames just have only a file directory item, and each file directory item can be preserved 8 important names and 3 extension name; And long filenames is made up of continuous several file directory items, wherein, a file directory item is arranged, and the pairing short filename of this long filenames is deposited in the inside, so this directory entry often is called as short directory entry; Other remaining directory entries are used to deposit the long filenames character string, so these file directory items often are called as long directory entry again.
There are information such as the filename that comprises this document, file attribute, file size, file storage location the pairing file directory item of each filename the inside.Link together filename and the pairing space of this document attribute a small bundle of straw, etc. for silkworms to spin cocoons on and just can hold the storage condition of a file fully, can orient all the elements of file through following step at hard disk:
(1) through the path find file place catalogue bunch;
(2) in the corresponding space of catalogue, compare filename, find file corresponding file directory entry;
(3) confirm the starting cluster and the file size of file through the file directory item;
(4) confirm file storing space according to bunch chain in the FAT table.
In long filenames mechanism, for compatible with 8.3 formatted file names, the composition of the file directory item of a long filenames is as shown in table 1 below:
Table 1
| N (at last with one) long directory entry |
| ...... |
| Second long directory entry |
| First long directory entry |
| The short directory entry (8.3 filename) that long filenames is corresponding |
Wherein each long directory entry structure (FAT Long Directory Entry Structure) is as shown in table 2 below:
Table 2
Wherein the short directory entry structure of long filenames correspondence is similar with the directory entry of traditional 8.3 forms, shown in the table 3 specific as follows:
Table 3
Such as; Comprise four with the corresponding complete file directory entry of filename " Create File With Longfilename.txt "; Wherein long directory entry needs three; Be used to preserve this long filenames character string (specifically as shown in table 2), and " CREATE～1TXT " (specifically as shown in table 3) by name of the file in the short directory entry, the filename of its short directory entry is to confirm according to the following steps:
(1) removes all spaces in the filename, become " CreateFileWithLongfilename.txt ".
(2) by the name rule, check, dispel, replace the unallowable instruction digit in the name.
(3) press 6 characters of the maximum interceptings of important name, and extension name (its. the back be an extension name) method of maximum 3 characters of intercepting, generating basic short name is " Create.txt ".
(4), for new short name adds the expansion sequence number, and all transfer the capitalization form to, like " CREATE～1.TXT " according to rule.
(5) if the existing file name is conflicted under new short name " CREATE～1.TXT " and the current goal catalogue; Need increase the expansion sequence number so; Like " CREATE～2.TXT ", " CREATE～3.TXT " ..., up to the current goal catalogue under the All Files name all no longer conflict.
Can know that according to above-mentioned steps (5) the short directory entry of long filenames needs just can confirm according to the filename under the current goal catalogue, therefore, needs the run-down target directory at least.
In addition, owing to do not allow under the same target directory to bear the same name, therefore, before creating filename, need to confirm whether there is file of the same name under the target directory, this also needs the scan objects catalogue just to know.
Moreover, in case confirm target directory down no duplication of name file and short directory entry also generated, also need travel through target directory to confirm the writing position of weak point directory entry.
When creating long filenames, come if isolate top three kinds of situation, need travel through the current goal catalogue at least three times.Repeatedly scanning traversal current goal catalogue is to read little blocks of data from disk continually, and the read data speed that this can have a strong impact on the Flash medium causes the constructive process required time long.The required time overhead of such processing mode does not include big as far as the stronger PC of processing power, be very huge but embedded system is created long filenames, some occasion or even unacceptable.
On the other hand, when confirming the expansion sequence number of newly-built short filename, temporary all similar short filenames are a kind of natural ways in the process of traversal current goal catalogue.If similar documents is very many, it is obviously very big to take to preserve the required memory headroom of the way of filename.Huge space expense often can't satisfy in the nervous relatively embedded system of resource especially memory source.
Here what deserves to be mentioned is: the position diagrammatic sketch is to utilize bit to represent the name situation of the short directory entry of the similar documents name under certain catalogue.When its value was " 0 ", the expansion sequence number of expression correspondence was also unoccupied; During for " 1 ", represent that this expansion sequence number used by certain similar documents name.The mark that the system that has has distributed " 0 " as the expansion sequence number, " 1 " as idle marker.(they be identical in essence, all be with one two states sign idle with distributed two kinds of situation.) the employed expansion sequence number of similar documents name under this catalogue, like CREATE～1.TXT, CREATE～2.TXT; CREATE～3.TXT ..., CREA～100.TXT; ... all there is bit corresponding with it in the diagrammatic sketch on the throne; Like this, constitute a set, be called a diagrammatic sketch by all pairing positions of expansion sequence numbers of similar documents name.Common available m*n units constitutes a diagrammatic sketch, and makes m*n equal always to expand sequence number.
[summary of the invention]
The technical matters that the present invention will solve is to provide a kind of method that embedded device is created FAT filename time and space expense that reduces.
The present invention is achieved in that a kind of method that embedded device is created FAT filename time and space expense that reduces, and may further comprise the steps:
The position that preparatory establishment filename can be deposited by first place under step 33, the record current goal catalogue;
Further; Step 32 is filled in institute's rheme diagrammatic sketch and is specially: the expansion sequence number of one by one that each filename is corresponding short directory entry deducts 1; And then, fill in position corresponding in the diagrammatic sketch as horizontal ordinate, remainder as ordinate with the merchant divided by 8 quotient and the remainder that obtain.
Further, the position that can deposit preparatory establishment filename in the step 33 comprises that file is by the position that stays after deleting under blank position and the current goal catalogue under the current goal catalogue.
The present invention has following advantage: diagrammatic sketch of definition in the embedded device internal memory; By the position diagrammatic sketch; The expansion sequence number of confirming to create in advance the corresponding short catalogue of filename, determine whether to exist the position three of file of the same name and definite store files to operate synchronously, thereby saved the time and the space of establishment FAT filename on embedded device widely.
[description of drawings]
Fig. 1 is the inventive method schematic flow sheet.
[embodiment]
Please, the present invention is described further in conjunction with a specific embodiment with reference to shown in Figure 1.
In order to narrate conveniently, be example still with preparatory establishment file " Create File WithLongfilename.txt " by name.
A kind of reduction embedded device is created the method for FAT filename (embedded device is created the FAT long filenames, comprises ASCII character and GBK sign indicating number, like the filename of forms such as longfile-name.mp3) time and space expense, may further comprise the steps:
Below in conjunction with a specific embodiment the present invention is described further.
The item number of the long directory entry that all each files under step 31, scanning traversal " Create File With Longfilename.txt " filename (the long directory entry of its " CreateFile With Longfilename.txt " filename is 3) place current goal catalogue are corresponding; File " with.txt ", " Create File With Shortfilename.txt ", " Create File With comename.txt " these three files are arranged under the hypothetical target catalogue; Then the long directory entry of file " with.txt " is 1; The long directory entry of file " Create File WithShortfilename.txt " is 3, and the long directory entry of file " Create File With comename.txt " is 3; Whether the item number of the file " with.txt " under the item number (3) that compares the corresponding long directory entry of " Create File With Longfilename.txt " filename one by one and the said target directory, " CreateFile With Shortfilename.txt ", " Create File With comename.txt " long directory entry that these three filenames are corresponding is equal; The long directory entry of file " with.txt " is 1, and unequal (then this document is not a similar file of creating filename in advance; Need not to compare); Then directly getting next filename " Create File With Shortfilename.txt " compares; Reduce comparison task like this, also just reduced the number of times of reading disk; And filename relatively is long more, and relatively speed is fast more, has avoided will determining whether to exist file of the same name, need carry out character string relatively; And character string word for word relatively is very time taking; The long directory entry of " Create File With Shortfilename.txt " is 3 and equates at this moment; The character string of then carrying out " Create File With Shortfilename.txt " character and " Create File With Longfilename.txt " more relatively determines whether of the same name, not of the same name; Then carry out the comparison of the long directory entry of " Create File With comename.txt " (long directory entry is 3) again; Equate; The character string of carrying out " Create File With comename.txt " character string and " Create File With Longfilename.txt " more relatively determines whether of the same name, not of the same name; After this moment, All Files all relatively finished, draw 2 similar filenames i.e. " Create File With Shortfilename.txt " and " Create File With comename.txt ", then carried out next procedure.
Table 4
As shown in table 5, be the position diagrammatic sketch that fills, which byte in the row number expression position diagrammatic sketch wherein is listed as and number representes the item in certain byte.Value in the diagrammatic sketch of position is the user mode of the expansion sequence number of certain similar documents name under certain current directory, and row and column correspondence has in the drawings been formed its similar extension name mark.As (1,0) this coordinate corresponding be 0, explain that the expansion sequence number of (1,0) this mark is unoccupied.As in the preceding text～2 be used, then corresponding mark position is that (0,1) should be set to 1.So, want the new files name now, search a diagrammatic sketch so; Find that first spare bits is (0; 0) position, its corresponding expansion sequence number are～1 (promptly equaling 1 according to formula m*8+n+1) so promptly can define position～1 to the expansion sequence number of this new files name short filename.
Table 5
| ? | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 |
| 2 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
| 3 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| ...... | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
What deserves to be mentioned is: (coding of simplified form of Chinese Character is GBK2312 when filename is Chinese; The speech encoding of other NON-ASCIIs can similarly be handled; Like Japanese, Korean, Latin etc.); For example: the unicode sign indicating number of " founding ceremony .rmvb " is BF AA B9 FA B4 F3 B5 E4 2E 72 6d 76 62 six binary numbers in front ASCII certainly not so, so just saying of capital and small letter can not be arranged; But; Can be through mapping; Be mapped to the ASCII zone to the Chinese sign indicating number zone in the unicode table, as BF through being mapped to unique position in the ascii table, so just can find a letter of correspondence; So just can have a capitalization corresponding with it, promptly operation is exactly that the Chinese name that will create in advance earlier converts unicode sign indicating number (just by the conversion of GBK2312 to unicode) into; Then the Chinese sign indicating number zone in the unicode table is mapped to the ASCII zone; Then, the unicode sign indicating number that each Chinese is corresponding obtains corresponding letter in the corresponding mapping position of ASCII regional search, capitalizes conversion and subsequent operation again.
The above is merely preferred embodiment of the present invention, and all equalizations of doing according to claim of the present invention change and modify, and all should belong to covering scope of the present invention.
Claims (3)
1. one kind is reduced the method that embedded device is created FAT filename time and space expense, it is characterized in that, may further comprise the steps:
Step 10, in the embedded device internal memory definition diagrammatic sketch;
Step 20, intercepting are created preceding 6 characters of filename in advance and are converted into capitalization, as preceding 6 characters of the corresponding short directory entry of preparatory establishment filename;
Step 30, begin to scan the current goal catalogue, carry out the task of newly-built preparatory establishment filename, in scanning process, handle below accomplishing synchronously:
Step 31, scanning traversal are created the item number of the corresponding long directory entry of all each filenames under the current goal catalogue of filename place in advance, and whether the item number of the corresponding long directory entry of each filename is equal under the item number of creating the corresponding long directory entry of filename one by one more in advance and the said target directory; The item number that carries out the corresponding long directory entry of first filename under the said target directory earlier compares; Unequal, the item number that then carries out the corresponding long directory entry of second filename of said target directory compares; Equate that the character string of then carrying out first filename and said preparatory establishment filename relatively comes to confirm to create filename in advance and whether first filename is of the same name; Be then to stop to create in advance the establishment processing of file; Otherwise the item number that carries out the corresponding long directory entry of second filename of said target directory compares; Relatively intact and do not exist under the situation of the same name when All Files name under the said target directory according to aforesaid way, change step 32 over to;
Step 32, retrieval and each similar filename of said preparatory establishment filename, the expansion sequence number of the short directory entry that similar each filename of basis and said preparatory establishment filename is corresponding one by one, correspondence is filled in institute's rheme diagrammatic sketch;
The position that preparatory establishment filename can be deposited by first place under step 33, the record current goal catalogue;
Step 34, to search institute's first value of rheme diagrammatic sketch be 0 spare bits, defines the n position that its spare bits is a m byte in the diagrammatic sketch, and the expansion sequence number of then creating the corresponding short directory entry of filename in advance is m*8+n+1;
Step 35, preceding 6 characters of creating in advance the corresponding short directory entry of filename in the step 20 are combined with said expansion sequence number; Produce last short directory entry title; And in the position of said step 33, write the complete name of preparatory establishment filename, accomplish the establishment of this document name.
2. reduction embedded device according to claim 1 is created the method for FAT filename time and space expense; It is characterized in that: step 32 is filled in institute's rheme diagrammatic sketch and is specially: the expansion sequence number of one by one that each filename is corresponding short directory entry deducts 1; And then, fill in position corresponding in the diagrammatic sketch as horizontal ordinate, remainder as ordinate with the merchant divided by 8 quotient and the remainder that obtain.
3. reduction embedded device according to claim 1 is created the method for FAT filename time and space expense, it is characterized in that: the position that can deposit preparatory establishment filename in the step 33 comprises that file is by the position that stays after deleting under blank position and the current goal catalogue under the current goal catalogue.
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| CN101051320A (en) * | 2007-05-11 | 2007-10-10 | 北京中星微电子有限公司 | File name generating method and device in file distribution system |
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| CN101051320A (en) * | 2007-05-11 | 2007-10-10 | 北京中星微电子有限公司 | File name generating method and device in file distribution system |
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| 李红卫.RTEMS存储管理的研究与改进.《微计算机应用》.2008,(第03期), * |
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