FATFS支持英文长文件名

╰半夏微凉° 2022-08-05 08:30 150阅读 0赞

这段时间在做SD卡的驱动以及在此基础上增加FAT32文件系统.

SD卡目前使用SDHC 16G的TF卡,读写擦功能都支持.

那么FAT32文件系统,我们可以在网上找到[开源的FAT文件系统][FAT]这个文件系统,目前很多人都在使用.

移植方面很简单,只要实现diskio.c里面的几个函数就可以了.

![Center][]

另外,还有一个配置文件ffconf.h这个文件,主要配置一些功能.如是否支持长文件名,中文编码等等。

所以我们要实现支持长的英文名字,是需要配置以下宏

/*---------------------------------------------------------------------------/
    / Locale and Namespace Configurations
    /---------------------------------------------------------------------------*/
    
    #define _CODE_PAGE	437
    /* This option specifies the OEM code page to be used on the target system.
    /  Incorrect setting of the code page can cause a file open failure.
    /
    /   1   - ASCII (No extended character. Non-LFN cfg. only)
    /   437 - U.S.
    /   720 - Arabic
    /   737 - Greek
    /   771 - KBL
    /   775 - Baltic
    /   850 - Latin 1
    /   852 - Latin 2
    /   855 - Cyrillic
    /   857 - Turkish
    /   860 - Portuguese
    /   861 - Icelandic
    /   862 - Hebrew
    /   863 - Canadian French
    /   864 - Arabic
    /   865 - Nordic
    /   866 - Russian
    /   869 - Greek 2
    /   932 - Japanese (DBCS)
    /   936 - Simplified Chinese (DBCS)
    /   949 - Korean (DBCS)
    /   950 - Traditional Chinese (DBCS)
    */
    
    
    #define	_USE_LFN	3
    #define	_MAX_LFN	255
    /* The _USE_LFN option switches the LFN feature.
    /
    /   0: Disable LFN feature. _MAX_LFN has no effect.
    /   1: Enable LFN with static working buffer on the BSS. Always NOT thread-safe.
    /   2: Enable LFN with dynamic working buffer on the STACK.
    /   3: Enable LFN with dynamic working buffer on the HEAP.
    /
    /  When enable the LFN feature, Unicode handling functions (option/unicode.c) must
    /  be added to the project. The LFN working buffer occupies (_MAX_LFN + 1) * 2 bytes.
    /  When use stack for the working buffer, take care on stack overflow. When use heap
    /  memory for the working buffer, memory management functions, ff_memalloc() and
    /  ff_memfree(), must be added to the project. */
    
    
    #define	_LFN_UNICODE	0
    /* This option switches character encoding on the API. (0:ANSI/OEM or 1:Unicode)
    /  To use Unicode string for the path name, enable LFN feature and set _LFN_UNICODE
    /  to 1. This option also affects behavior of string I/O functions. */

然后将option目录下的syscall.c、unicode.c包含到工程里面.

由于需要支持到内存动态分配等原因,所以修改syscall.c文件的相关函数.如下图:

![Center 1][]

然后进行编译=======>通过！

然后,你写一个长文件名,如test0123456789.TXT，并往里面写内容.完全没有问题.读文件也是没有问题.

但是如果你要读文件的内容时,你要注意一下,因为你需要知道要读取的文件大小.也许你会使用

FRESULT f_stat (
    	const TCHAR* path,	/* Pointer to the file path */
    	FILINFO* fno		/* Pointer to file information to return */
    )

通常代码,你会如下写

FILINFO fno;
    	if(f_stat( "0:Test1234567890.txt",&fno))
    	{
    			DEBUG_MSG(MAIN_DEBUG,("f_stat Fail !!!!\r\n"));
    	}
    	else
    	{
    		DEBUG_MSG(MAIN_DEBUG,("%s Size %d .\r\n",fno.fname,fno.fsize));
    		if(f_open(&file, "0:Test1234567890.txt", FA_OPEN_EXISTING | FA_READ)) 
    		{
    			DEBUG_MSG(MAIN_DEBUG,("f_open File Fail .\r\n"));
    		}
    		else
    		{
    			char *pBuffer = malloc(fno.fsize);
    			memset(pBuffer,0,fno.fsize);
    			if(pBuffer)
    			{
    				u32 kk = 0;
    				if(f_read(&file, pBuffer,fno.fsize, &bw))
    				{
    					DEBUG_MSG(MAIN_DEBUG,("f_read Fail !!!!\r\n"));
    				}	
    				while(kk < fno.fsize)
    				{
    					DEBUG_MSG(MAIN_DEBUG,("%c",pBuffer[kk++]));
    				}
    				DEBUG_MSG(MAIN_DEBUG,("\r\nRead Size %d .\r\n",bw));
    				free(pBuffer);
    				pBuffer = NULL;
    			}
    
    			f_close(&file);
    		}	
    	}

这个代码逻辑是没有什么大问题的.但是如果你用IAR debug方式,运行你会发现当程序异常了.

你深入调试会发现一个问题,文件大小竟然非常非常大.这个数值貌似没有赋值.

当你跟踪到如下代码

/*-----------------------------------------------------------------------*/
    /* Get file information from directory entry                             */
    /*-----------------------------------------------------------------------*/
    #if _FS_MINIMIZE <= 1 || _FS_RPATH >= 2
    static
    void get_fileinfo (		/* No return code */
    	DIR* dp,			/* Pointer to the directory object */
    	FILINFO* fno	 	/* Pointer to the file information to be filled */
    )
    {
    	UINT i;
    	TCHAR *p, c;
    	BYTE *dir;
    #if _USE_LFN
    	WCHAR w, *lfn;
    #endif
    
    	p = fno->fname;
    	if (dp->sect) {		/* Get SFN */
    		dir = dp->dir;
    		i = 0;
    		while (i < 11) {		/* Copy name body and extension */
    			c = (TCHAR)dir[i++];
    			if (c == ' ') continue;				/* Skip padding spaces */
    			if (c == RDDEM) c = (TCHAR)DDEM;	/* Restore replaced DDEM character */
    			if (i == 9) *p++ = '.';				/* Insert a . if extension is exist */
    #if _USE_LFN
    			if (IsUpper(c) && (dir[DIR_NTres] & (i >= 9 ? NS_EXT : NS_BODY)))
    				c += 0x20;			/* To lower */
    #if _LFN_UNICODE
    			if (IsDBCS1(c) && i != 8 && i != 11 && IsDBCS2(dir[i]))
    				c = c << 8 | dir[i++];
    			c = ff_convert(c, 1);	/* OEM -> Unicode */
    			if (!c) c = '?';
    #endif
    #endif
    			*p++ = c;
    		}
    		fno->fattrib = dir[DIR_Attr];				/* Attribute */
    		fno->fsize = LD_DWORD(dir + DIR_FileSize);	/* Size */
    		fno->fdate = LD_WORD(dir + DIR_WrtDate);	/* Date */
    		fno->ftime = LD_WORD(dir + DIR_WrtTime);	/* Time */
    	}
    	*p = 0;		/* Terminate SFN string by a \0 */
    
    #if _USE_LFN
    	if (fno->lfname) {
    		i = 0; p = fno->lfname;
    		if (dp->sect && fno->lfsize && dp->lfn_idx != 0xFFFF) {	/* Get LFN if available */
    			lfn = dp->lfn;
    			while ((w = *lfn++) != 0) {		/* Get an LFN character */
    #if !_LFN_UNICODE
    				w = ff_convert(w, 0);		/* Unicode -> OEM */
    				if (!w) { i = 0; break; }	/* No LFN if it could not be converted */
    				if (_DF1S && w >= 0x100)	/* Put 1st byte if it is a DBC (always false on SBCS cfg) */
    					p[i++] = (TCHAR)(w >> 8);
    #endif
    				if (i >= fno->lfsize - 1) { i = 0; break; }	/* No LFN if buffer overflow */
    				p[i++] = (TCHAR)w;
    			}
    		}
    		p[i] = 0;	/* Terminate LFN string by a \0 */
    	}
    #endif
    }
    #endif /* _FS_MINIMIZE <= 1 || _FS_RPATH >= 2 */

你会发现“fno->lfsize”这个值很大。如果你一路从f\_stat函数跟踪进来,你会知道这整个过程“fno->lfsize”都没有被赋值过.因此,解决这个问题的方法是,开始的时候对"FILINFO fno"进行赋值.可以写成"FILINFO fno = \{0\};"

至此,读文件内容也正常了.补充一点,当不支持长命名文件时,都是很正常（但或许存在风险,因此无论如何对该结构体变量都需要进行赋初值）.

来自:[http://blog.csdn.net/lan120576664][http_blog.csdn.net_lan120576664]

[FAT]: http://elm-chan.org/fsw/ff/00index_e.html
[Center]: /images/20220731/5ebbf5a1c1534d3781888fd5b5e3dd68.png
[Center 1]: /images/20220731/d39302b9f44846d1ad5a088d5690b33b.png
[http_blog.csdn.net_lan120576664]: http://blog.csdn.net/lan120576664