鸿蒙轻内核M核源码分析系列二一 05 文件系统FatFS 原创精华

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发布于 2022-1-9 17:50

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鸿蒙轻内核M核源码分析系列二一 05 文件系统FatFS

【本文正在参与优质创作者激励】

3、LiteOS-M FATFS的文件系统操作接口

快速记录下各个操作接口，对每个接口的用途用法不再描述。可以参考之前的系列文章，《鸿蒙轻内核M核源码分析系列十九 Musl LibC》中介绍了相关的接口，那些接口会调用VFS文件系统中操作接口，然后进一步调用FatFS文件操作接口。

3.1 挂载和卸载操作

先看下挂载操作，FatFS支持重新挂载操作。如果挂载选项包含MS_REMOUNT时，会调用函数Remount()重新挂载。函数Remount()中，⑴处调用FsPartitionMatch()获取卷索引，⑵处如果卷未被挂载，不允许重新挂载，返回错误码。⑶处设置对应的卷是否可读可写标记。由此看来，重新挂载，主要是更新卷的可读可写能力。

看下挂载函数fatfs_mount()，⑷处开始判断参数有效性，不能为空，文件系统类型必须为“fat”，⑸处调用FsPartitionMatch()获取卷索引，⑹处如果卷已经被挂载，则返回错误码。⑺处调用f_mount()实现挂载，第3个参数1表示立即挂载。⑻设置对应的卷是否可读可写标记。

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;
}
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接下来，看下卸载操作。函数fatfs_umount()中，先进行参数有效性，是否挂载等基础检查，⑴处调用函数f_checkopenlock()来判断要卸载的卷中是否有打开的文件或目录，⑵处调用f_mount()，第一个参数为NULL，表示卸载target指定的文件系统；，第3个参数0表示不需要挂载。如果卸载错误，转换相应的错误码。⑶处如果磁盘访问窗口（Disk access window for Directory）不为空，执行相应的释放操作。⑷处把文件卷数组对应的元素置零。

函数CloseAll()根据文件卷编号，遍历每一个打开的文件和目录进行关闭。函数fatfs_umount2()中，⑸处表示支持的卸载选项有：MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW。⑹处处理强制卸载的情形，会首先关闭打开的文件和目录，然后再去执行⑺实现卸载操作。

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;
}

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3.2 文件目录操作接口

文件目录操作接口包含fatfs_mkdir、fatfs_unlink、fatfs_rmdir、fatfs_readdir、fatfs_closedir、fatfs_open、fatfs_close等等，会进一步调用FatFS的文件目录操作接口进行封装，代码比较简单，自行阅读即可，部分代码片段如下。

......
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;
}
......
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