鴻蒙輕內核M核源碼分析系列二一 03 文件系統FatFS(2)

2.4 判斷文件卷是否可寫

函數FsCheckByPath()、FsCheckByID()用于判斷文件卷是否可寫，傳遞參數不同。前者傳入的是文件路徑，轉化為卷索引后判斷。后者傳入的是掛載編號，遍歷每一個卷，判斷相應卷的編號與傳入參數是否相等。

static bool FsCheckByPath(const char *path) { INT32 index; index = FsPartitionMatch(path, PATH_NAME); if (index == FS_FAILURE) { return FS_FAILURE; } return g_volWriteEnable[index]; } static bool FsCheckByID(int id) { INT32 index; for (index = 0; index < FF_VOLUMES; index++) { if (g_fatfs[index].id == id) { return g_volWriteEnable[index]; } } return false; }

2.5 標簽轉換

函數FatFsGetMode()用于把POSIX格式的文件打開標簽轉換為FatFS文件系統格式的文件打開標簽。FatfsErrno()把FatFS文件系統格式的錯誤號轉換為POSIX格式的錯誤號。

static unsigned int FatFsGetMode(int oflags) { UINT32 fmode = FA_READ; if ((UINT32)oflags & O_WRONLY) { fmode |= FA_WRITE; } if (((UINT32)oflags & O_ACCMODE) & O_RDWR) { fmode |= FA_WRITE; } /* Creates a new file if the file is not existing, otherwise, just open it. */ if ((UINT32)oflags & O_CREAT) { fmode |= FA_OPEN_ALWAYS; /* Creates a new file. If the file already exists, the function shall fail. */ if ((UINT32)oflags & O_EXCL) { fmode |= FA_CREATE_NEW; } } /* Creates a new file. If the file already exists, its length shall be truncated to 0. */ if ((UINT32)oflags & O_TRUNC) { fmode |= FA_CREATE_ALWAYS; } return fmode; } static int FatfsErrno(int result) { INT32 status = 0; if (result < 0) { return result; } /* FatFs errno to Libc errno */ switch (result) { case FR_OK: break; case FR_NO_FILE: case FR_NO_PATH: case FR_NO_FILESYSTEM: status = ENOENT; break; ...... default: status = result; break; } return status; }

3、LiteOS-M FATFS的文件系統操作接口

快速記錄下各個操作接口，對每個接口的用途用法不再描述?？梢詤⒖贾暗南盗形恼?，《鴻蒙輕內核M核源碼分析系列十九 Musl LibC》中介紹了相關的接口，那些接口會調用VFS文件系統中操作接口，然后進一步調用FatFS文件操作接口。

3.1 掛載和卸載操作

先看下掛載操作，FatFS支持重新掛載操作。如果掛載選項包含MS_REMOUNT時，會調用函數Remount()重新掛載。函數Remount()中，⑴處調用FsPartitionMatch()獲取卷索引，⑵處如果卷未被掛載，不允許重新掛載，返回錯誤碼。⑶處設置對應的卷是否可讀可寫標記。由此看來，重新掛載，主要是更新卷的可讀可寫能力。

看下掛載函數fatfs_mount()，⑷處開始判斷參數有效性，不能為空，文件系統類型必須為“fat”，⑸處調用FsPartitionMatch()獲取卷索引，⑹處如果卷已經被掛載，則返回錯誤碼。⑺處調用f_mount()實現掛載，第3個參數1表示立即掛載。⑻設置對應的卷是否可讀可寫標記。

static int Remount(const char *path, unsigned long mountflags) { INT32 index; ⑴ index = FsPartitionMatch(path, PART_NAME); if (index == FS_FAILURE) { PRINTK("Wrong volume path!\r\n"); errno = ENOENT; return FS_FAILURE; } /* remount is not allowed when the device is not mounted. */ ⑵ if (g_fatfs[index].fs_type == 0) { errno = EINVAL; return FS_FAILURE; } ⑶ g_volWriteEnable[index] = (mountflags & MS_RDONLY) ? FALSE : TRUE; return FS_SUCCESS; } ...... int fatfs_mount(const char *source, const char *target, const char *filesystemtype, unsigned long mountflags, const void *data) { INT32 index; FRESULT res; INT32 ret; ⑷ if ((target == NULL) || (filesystemtype == NULL)) { errno = EFAULT; return FS_FAILURE; } ret = FsLock(); if (ret != 0) { errno = ret; return FS_FAILURE; } if (mountflags & MS_REMOUNT) { ret = Remount(target, mountflags); goto OUT; } if (strcmp(filesystemtype, "fat") != 0) { errno = ENODEV; ret = FS_FAILURE; goto OUT; } ⑸ index = FsPartitionMatch(target, VOLUME_NAME); if (index == FS_FAILURE) { errno = ENODEV; ret = FS_FAILURE; goto OUT; } /* If the volume has been mounted */ ⑹ if (g_fatfs[index].fs_type != 0) { errno = EBUSY; ret = FS_FAILURE; goto OUT; } ⑺ res = f_mount(&g_fatfs[index], target, 1); if (res != FR_OK) { errno = FatfsErrno(res); ret = FS_FAILURE; goto OUT; } ⑻ g_volWriteEnable[index] = (mountflags & MS_RDONLY) ? FALSE : TRUE; ret = FS_SUCCESS; OUT: FsUnlock(); return ret; }

接下來，看下卸載操作。函數fatfs_umount()中，先進行參數有效性，是否掛載等基礎檢查，⑴處調用函數f_checkopenlock()來判斷要卸載的卷中是否有打開的文件或目錄，⑵處調用f_mount()，第一個參數為NULL，表示卸載target指定的文件系統；，第3個參數0表示不需要掛載。如果卸載錯誤，轉換相應的錯誤碼。⑶處如果磁盤訪問窗口（Disk access window for Directory）不為空，執行相應的釋放操作。⑷處把文件卷數組對應的元素置零。

函數CloseAll()根據文件卷編號，遍歷每一個打開的文件和目錄進行關閉。函數fatfs_umount2()中，⑸處表示支持的卸載選項有：MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW。⑹處處理強制卸載的情形，會首先關閉打開的文件和目錄，然后再去執行⑺實現卸載操作。

int fatfs_umount(const char *target) { FRESULT res; INT32 ret; INT32 index; if (target == NULL) { errno = EFAULT; return FS_FAILURE; } ret = FsLock(); if (ret != 0) { errno = ret; return FS_FAILURE; } index = FsPartitionMatch(target, VOLUME_NAME); if (index == FS_FAILURE) { errno = ENOENT; ret = FS_FAILURE; goto OUT; } /* The volume is not mounted */ if (g_fatfs[index].fs_type == 0) { errno = EINVAL; ret = FS_FAILURE; goto OUT; } /* umount is not allowed when a file or diretory is opened. */ ⑴ if (f_checkopenlock(index) != FR_OK) { errno = EBUSY; ret = FS_FAILURE; goto OUT; } ⑵ res = f_mount((FATFS *)NULL, target, 0); if (res != FR_OK) { errno = FatfsErrno(res); ret = FS_FAILURE; goto OUT; } ⑶ if (g_fatfs[index].win != NULL) { ff_memfree(g_fatfs[index].win); } ⑷ (void)memset_s(&g_fatfs[index], sizeof(FATFS), 0x0, sizeof(FATFS)); ret = FS_SUCCESS; OUT: FsUnlock(); return ret; } static int CloseAll(int index) { INT32 i; FRESULT res; for (i = 0; i < FAT_MAX_OPEN_FILES; i++) { if (g_fileNum <= 0) { break; } if ((g_handle[i].useFlag == 1) && (g_handle[i].fil.obj.fs == &g_fatfs[index])) { res = f_close(&g_handle[i].fil); if (res != FR_OK) { errno = FatfsErrno(res); return FS_FAILURE; } (void)memset_s(&g_handle[i], sizeof(FatHandleStruct), 0x0, sizeof(FatHandleStruct)); g_fileNum--; } } for (i = 0; i < FAT_MAX_OPEN_DIRS; i++) { if (g_dirNum <= 0) { break; } if (g_dir[i].obj.fs == &g_fatfs[index]) { res = f_closedir(&g_dir[i]); if (res != FR_OK) { errno = FatfsErrno(res); return FS_FAILURE; } (void)memset_s(&g_dir[i], sizeof(DIR), 0x0, sizeof(DIR)); g_dirNum--; } } return FS_SUCCESS; } int fatfs_umount2(const char *target, int flag) { INT32 index; INT32 ret; UINT32 flags; FRESULT res; if (target == NULL) { errno = EFAULT; return FS_FAILURE; } ⑸ flags = MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW; if ((UINT32)flag & ~flags) { errno = EINVAL; return FS_FAILURE; } ret = FsLock(); if (ret != 0) { errno = ret; return FS_FAILURE; } index = FsPartitionMatch(target, VOLUME_NAME); if (index == FS_FAILURE) { errno = ENOENT; ret = FS_FAILURE; goto OUT; } /* The volume is not mounted */ if (g_fatfs[index].fs_type == 0) { errno = EINVAL; ret = FS_FAILURE; goto OUT; } ⑹ if ((UINT32)flag & MNT_FORCE) { ret = CloseAll(index); if (ret != FS_SUCCESS) { goto OUT; } } ⑺ res = f_mount((FATFS *)NULL, target, 0); if (res != FR_OK) { errno = FatfsErrno(res); ret = FS_FAILURE; goto OUT; } if (g_fatfs[index].win != NULL) { ff_memfree(g_fatfs[index].win); } (void)memset_s(&g_fatfs[index], sizeof(FATFS), 0x0, sizeof(FATFS)); ret = FS_SUCCESS; OUT: FsUnlock(); return ret; }

3.2 文件目錄操作接口

文件目錄操作接口包含fatfs_mkdir、fatfs_unlink、fatfs_rmdir、fatfs_readdir、fatfs_closedir、fatfs_open、fatfs_close等等，會進一步調用FatFS的文件目錄操作接口進行封裝，代碼比較簡單，自行閱讀即可，部分代碼片段如下。

...... int fatfs_close(int fd) { FRESULT res; INT32 ret; ret = FsLock(); if (ret != 0) { errno = ret; return FS_FAILURE; } if (!IsValidFd(fd)) { FsUnlock(); errno = EBADF; return FS_FAILURE; } if (g_handle[fd].fil.obj.fs == NULL) { FsUnlock(); errno = ENOENT; return FS_FAILURE; } res = f_close(&g_handle[fd].fil); if (res != FR_OK) { PRINTK("FAT close err 0x%x!\r\n", res); FsUnlock(); errno = FatfsErrno(res); return FS_FAILURE; } #if !FF_FS_TINY if (g_handle[fd].fil.buf != NULL) { (void)ff_memfree(g_handle[fd].fil.buf); } #endif (void)memset_s(&g_handle[fd], sizeof(FatHandleStruct), 0x0, sizeof(FatHandleStruct)); if (g_fileNum > 0) { g_fileNum--; } FsUnlock(); return FS_SUCCESS; } ......

小結

本文介紹了FatFS的結構體和全局變量，全局變量的操作接口，分析了下FatFS文件操作接口。時間倉促和能力關系，如有失誤，歡迎指正。感謝閱讀，如有任何問題、建議，都可以博客下留言給我，謝謝。

參考資料

HarmonyOS Device>文檔指南>基礎能力-FatFS

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版權聲明：本文內容由網絡用戶投稿，版權歸原作者所有，本站不擁有其著作權，亦不承擔相應法律責任。如果您發現本站中有涉嫌抄襲或描述失實的內容，請聯系我們jiasou666@gmail.com 處理，核實后本網站將在24小時內刪除侵權內容。