电子技术论坛_中国专业的电子工程师学习交流社区-中电网技术论坛

标题: FatFs源码剖析（3） [打印本页]

作者: yuyang911220 时间: 2016-7-22 21:02 标题: FatFs源码剖析（3）

http://www.openedv.com/posts/list/27427.htm

//计算根目录起始扇区、数据起始扇区(物理扇区地址)
fatend = fs->sects_fat * fs->n_fats + fs->fatbase;
if (fat == FS_FAT32) {
fs->dirbase = LD_DWORD(&(fs->win[0x2C])); /* Directory start cluster */
fs->database = fatend; /* Data start sector (physical) */
} else {
fs->dirbase = fatend; /* Directory start sector (physical) */
fs->database = fs->n_rootdir / 16 + fatend; /* Data start sector (physical) */
}
//最大簇号
fs->max_clust = /* Maximum cluster number */
(LD_DWORD(&(fs->win[0x20])) - fs->database + sect) / fs->sects_clust + 2;
return FR_OK;
}
/*-----------------------*/
/* Open or Create a File */
FRESULT f_open (
FIL *fp, /* ointer to the buffer of new file object to create */
const char *path, /* ointer to the file path */
BYTE mode /* Access mode and file open mode flags */
)
{
FRESULT res;
BYTE *dir;
DIR dirscan;
char fn[8+3+1]; //8.3 DOS文件名
FATFS *fs = FatFs;
/*首先初始化SD卡，检测文件系统类型，初始化FATFS对象*/
if ((res = check_mounted()) != FR_OK) return res;
#ifndef _FS_READONLY
//如果磁盘设置为写保护，则返回错误码:FR_WRITE_PROTECTED
if ((mode & (FA_WRITE|FA_CREATE_ALWAYS)) && (disk_status() & STA_PROTECT))
return FR_WRITE_PROTECTED;
#endif
//根据用户提供的文件路径path，将文件名对应的目录项及其整个扇区读取到win[]中，
//并填充目录项dirscan、标准格式的文件名fn，以及目录项在win[]中的字节偏移量dir
res = trace_path(&dirscan, fn, path, &dir); /* Trace the file path */
#ifndef _FS_READONLY
/* Create or Open a File */
if (mode & (FA_CREATE_ALWAYS|FA_OPEN_ALWAYS)) {
DWORD dw;
//如果文件不存在，则强制新建文件
if (res != FR_OK) { /* No file, create new */
mode |= FA_CREATE_ALWAYS;
if (res != FR_NO_FILE) return res;
dir = reserve_direntry(&dirscan); /* Reserve a directory entry */
if (dir == NULL) return FR_DENIED;
memcpy(dir, fn, 8+3); /* Initialize the new entry */
*(dir+12) = fn[11];
memset(dir+13, 0, 32-13);
}
else { /* File already exists */
if ((dir == NULL) || (*(dir+11) & (AM_RDO|AM_DIR))) /* Could not overwrite (R/O or DIR) */
return FR_DENIED;
//如果文件存在，但又以FA_CREATE_ALWAYS方式打开文件，则重写文件
if (mode & FA_CREATE_ALWAYS) { /* Resize it to zero */
dw = fs->winsect; /* Remove the cluster chain */
if (!remove_chain(((DWORD)LD_WORD(dir+20) << 16) | LD_WORD(dir+26))
|| !move_window(dw) )
return FR_RW_ERROR;
ST_WORD(dir+20, 0); ST_WORD(dir+26, 0); /* cluster = 0 */
ST_DWORD(dir+28, 0); /* size = 0 */
}
}
//如果是强制新建文件操作，则还需更新时间和日期
if (mode & FA_CREATE_ALWAYS) {
*(dir+11) = AM_ARC;
dw = get_fattime();
ST_DWORD(dir+14, dw); /* Created time */
ST_DWORD(dir+22, dw); /* Updated time */
fs->dirtyflag = 1;
}
}
/* Open a File */
else {
#endif
if (res != FR_OK) return res; /* Trace failed */
//如果打开的是一个目录文件，则返回错误码:FR_NO_FILE
if ((dir == NULL) || (*(dir+11) & AM_DIR)) /* It is a directory */
return FR_NO_FILE;
#ifndef _FS_READONLY
//如果以FA_WRITE方式打开Read-Only属性的文件，则返回错误码:FR_DENIED
if ((mode & FA_WRITE) && (*(dir+11) & AM_RDO)) /* R/O violation */
return FR_DENIED;
}
#endif
//填充FIL文件结构体参数
#ifdef _FS_READONLY
fp->flag = mode & (FA_UNBUFFERED|FA_READ);
#else
fp->flag = mode & (FA_UNBUFFERED|FA_WRITE|FA_READ);
fp->dir_sect = fs->winsect; /* ointer to the directory entry */
fp->dir_ptr = dir;
#endif
fp->org_clust = ((DWORD)LD_WORD(dir+20) << 16) | LD_WORD(dir+26); /* File start cluster */
fp->fsize = LD_DWORD(dir+28); /* File size */
fp->fptr = 0; /* File ptr */
//这一步很重要，它将直接导致f_read和f_write操作中的逻辑顺序
fp->sect_clust = 1; /* Sector counter */
fs->files++;
return FR_OK;
}

作者: yuchengze 时间: 2016-8-21 14:28

很好的代码分享，感谢楼主分享

欢迎光临电子技术论坛_中国专业的电子工程师学习交流社区-中电网技术论坛 (http://bbs.eccn.com/)