create

Create a writable persistent overlay device on top of another block device.

namespace CheerpX {
  class OverlayDevice {
    static async create(
      baseDevice: Device,
      overlayDevice: Device
    ): Promise<OverlayDevice>;
  }
}

Parameters

• baseDevice (Device) - The underlying device (e.g., HttpBytesDevice, IDBDevice) that serves as the base layer for the filesystem.

• overlayDevice (Device) - The writable layer that will overlay the base device, enabling persistent changes.

Returns

CheerpX.OverlayDevice.create returns a Promise that resolves to an instance of the OverlayDevice. The OverlayDevice allows you to overlay a writable layer on top of the base device, enabling persistent changes while still accessing the base data.

Example

Create an OverlayDevice instance to combine a HttpBytesDevice for streaming data from an HTTP source and an IDBDevice for caching and persistent local storage.

// Create a read-only HttpBytesDevice for streaming disk blocks via HTTP
const httpDevice = await CheerpX.HttpBytesDevice.create("/cheerpXImage.ext2");

// Create an IDBDevice for local persistent storage
const idbDevice = await CheerpX.IDBDevice.create("block_idbDevice");

// Create an OverlayDevice to combine the two devices
const overlayDevice = await CheerpX.OverlayDevice.create(httpDevice, idbDevice);

// Mount the overlay device in the CheerpX environment as an ext2 filesystem
const cx = await CheerpX.Linux.create({
  mounts: [{ type: "ext2", path: "/", dev: overlayDevice }],
});

In this example, the OverlayDevice provides a writable layer on top of the HttpBytesDevice (which serves as a read-only block device for streaming), allowing changes to be stored locally via the IDBDevice.

For more information, please check out the Files and File system guide. This guide provides more details on how to work with files and directories in CheerpX.