OpenHarmony distributed file system (hmdfs) provides cross-device file access capabilities applicable to the following scenarios:
OpenHarmony distributed file system (hmdfs) provides cross-device file access capabilities in the following scenarios:
- The user can use the editing software on one device to edit the files on another device.
- The user uses the editing software on one device to edit the files on another device.
- Music stored on a tablet can be directly viewed and played by a in-car system.
- Music stored on a tablet can be directly viewed and played by an in-car system.
- The user can use a tablet to view the photos taken by another device.
- The user uses a tablet to view the photos taken by another device.
The hmdfs provides a globally consistent access view for each device dynamically connected to a network via DSoftBus and allows you to implement high-performance read and write operations on files with low latency by using basic file system APIs.
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- distributedfile_daemon: listens for device online status, establishes links over DSoftBus, and applies data transfer policies based on the security level of the device.
- hmdfs: implements a network file system in the kernel, providing cache management, file access, metadata management, and conflict management.
-Buffer management
- After devices are connected to form a Virtual Device, hmdfs provides file access capabilities, but does not proactively transmit or copy files. Active copy is required when an application needs to save data to a local directory.
- hmdfs: implements a network file system in the kernel and provides cache management, file access, metadata management, and conflict management.
-Cache management
- After devices are connected to form a Virtual Device, the hmdfs provides file access capabilities, but does not proactively transmit or copy files. Active copy is required when an application needs to save data to a local directory.
- The hmdfs ensures close-to-open cache consistency, which allows data to flushed when a client closes a file. Then, the latest data can be read when the file is opened on any other client. The hmdfs does not ensure real-time consistency of the file content.
- If data written at the peer end has not been flushed to the local end in a timely manner due to network problems, the file system flushes the data to the local end upon the next network access. However, if the data has been modified on the remote end, only the latest data can be flushed.
- If data written at the remote end has not been flushed to the local end in a timely manner due to network problems, the file system flushes the data to the local end upon the next network access. However, if the data has been modified on the remote end, only the latest data can be flushed.
- File access
- OpenHarmony provides the same interface, [ohos.file.fs](../reference/apis/js-apis-file-fs.md), for accessing files in the local and distributed file systems.
- OpenHarmony provides the unified [ohos.file.fs](../reference/apis/js-apis-file-fs.md) for accessing files in the local and distributed file systems.
- The files in the local file system are accessed in overlay mode.
- The files on another device are accessed over a synchronous network.
> **NOTE**
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- Metadata management
- In distributed networking, when a file is created, deleted, or modified on a client, the latest file can be viewed on another client. The speed varies depending on the network status.
- If a device goes offline, its data is no longer visible to other devices. However, due to the delay in sensing the device offline, the files of some offline devices may also be visible to other devices. Therefore, you need to consider the network delay in application development.
- Conflict Handling
- If a file on the local end and a file on the remote end have the same name, the file on the remote end will be renamed.
- If multiple remote devices have files of the same name, the name of the file with the smallest device access ID is retained and the files on other devices will be renamed.
- In the networking scenario, the directory tree has remote files. If "duplicate file name" is displayed when a file is created,
-the conflict file is renamed "_conflict_dev_ID". The ID automatically increases from 1.
- If a local directory has the same name as a remote directory, "_remote_directory" will be added to the end of the peer directory.
- Conflict management
- If a file name conflict occurs on the local and remote devices, the file on the remote device is renamed.
- If a file name conflict occurs between multiple remote devices, the name of the file with the smallest device access ID is retained and the files on other devices are renamed.
- If the directory tree already has remote files in networking scenario, a file with duplicate file name cannot be created successfully.
-The conflict files are renamed in "_conflict_dev_ID" format. The IDs automatically increment from 1.
- If a local directory and a remote directory have the same name, it does not yield a conflict. If the two directories have files with the same name, "_remote_directory" is added to the end of the remote directory.
The distributed file system provides cross-device file access capabilities for applications. For the same application installed on multiple devices, you can implement read and write of the files in the application's distributed directory (**/data/storage/el2/distributedfiles/**) across devices by using [ohos.file.fs](app-file-access.md). For example, device A and device B are installed with the same application. After device A and device B are connected to form a Virtual Device, the application on device A can access the files of the same application on Device B. What you need to do is place the files to the distributed directory.
The distributed file system provides cross-device file access capabilities for applications. For the same application installed on multiple devices that form a Super Device, you can use [ohos.file.fs](app-file-access.md) APIs to implement read and write of the files in the application's distributed directory (**/data/storage/el2/distributedfiles/**).
## How to Develop
For example, device A and device B are installed with the same application. After device A and device B are connected to form a Super Device, the application on device A can access the files in the distributed directory of the same application on Device B.
1. Complete distributed networking for the devices.
Connect the devices to a LAN, and complete authentication of the devices. The devices must have the same account number.
## How to Develop
1. Connect the devices to form a Super Device.
Connect the devices to a LAN, and complete authentication of the devices. The devices must have the same account number.
2. Implement cross-device access to the files of the same application.
Place the files in the **distributedfiles/** directory of the application sandbox to implement access from difference devices.
For example, create a test file in the **distributedfiles/** directory on device A and write data to the file. For details about how to obtain the context in the example, see [Obtaining the Context of UIAbility](../application-models/uiability-usage.md#obtaining-the-context-of-uiability).
For example, create a file in the **distributedfiles/** directory on device A and write data to the file. For details about how to obtain the application context, see [Obtaining the Context of UIAbility](../application-models/uiability-usage.md#obtaining-the-context-of-uiability).
# Setting the Security Level of a Distributed File
The security capabilities vary with devices. For example, small embedded devices provide fewer security capabilities than tablets. The security requirements also vary with data. For example, personal health information and bank card information are not expected to be accessed by devices of lower security levels. OpenHarmony provides a complete set of standards for data and device classification and custom data transfer policies for different devices. For details, see [Data Security Labels and Device Security Levels](../database/access-control-by-device-and-data-level.md).
The security capabilities vary with devices. For example, small embedded devices provide fewer security capabilities than tablets. The security requirements also vary with data. For example, personal health information and bank card information are not expected to be accessed by devices of lower security levels. OpenHarmony provides a complete set of data and device classification standards and custom data transfer policies for different devices. For details, see [Access Control by Device and Data Level](../database/access-control-by-device-and-data-level.md).
## Available APIs
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| setSecurityLabel | Sets a security label for a file.| Method| √ | √ |
| getSecurityLabel | Obtains the security label of a file.| Method| √ | √ |
| setSecurityLabel | Sets a security label for a file.| Method| √ | √ |
| getSecurityLabel | Obtains the security label of a file.| Method| √ | √ |
> **NOTICE**
> **NOTE**
>
> 1. In distributed networking, a device can view the files that do not match its security level but cannot access them.
> - In distributed networking, a device can view the files that do not match its security level but cannot access them.
>
> 2. The default security level of the distributed file system data is S3. Applications can set the security level of files.
> - The default security level of the distributed file system data is S3. Applications can set the security level of files.
## Development Example
Obtain the sandbox path of the file and set the data security label. For details about how to obtain the context in the example, see [Obtaining the Context of UIAbility](../application-models/uiability-usage.md#obtaining-the-context-of-uiability).
Obtain the sandbox path of a file and set the data security label. For details about how to obtain the context, see [Obtaining the Context of UIAbility](../application-models/uiability-usage.md#obtaining-the-context-of-uiability).
