node-ext2fs uses the e2fsprogs project to provide access to ext filesystem from javascript.

The node- in node-ext2fs is here because it was a native node module until v3.0.0 (excluded). Since v3.0.0, it is a WebAssembly module built with emscripten.

Some things you can do with this module:

• Read/write files in a filesystem image directly without mounting
• Use familiar APIs, node-ext2fs has the exact same interface as node's fs module
• Combine node-ext2fs filesystem streams with host filesystem streams (e.g copy files)
• Create a tar archive from a filesystem image
• Perform a TRIM operation to obtain discard regions of a filesystem

Simply install node-ext2fs using npm:

$ npm install node-ext2fs

Mount a disk image and use the returned fs object. The fs returned object behaves like node's fs except it doesn't provide any xxxxSync method. You can also issue DISCARD requests using the fs async trim() method.

See the example below.

const { withMountedDisk } = require('ext2fs');
const { FileDisk, withOpenFile } = require('file-disk');

async function main() {
  const diskImage = '/some/disk.image';
  const offset = 272629760;  // offset of the ext partition you want to mount in that disk image
  try {
    await withOpenFile(diskImage, 'r', async (handle) => {
      const disk = new FileDisk(handle);
      await withMountedDisk(disk, offset, async ({promises:fs}) => {
        // List files
        console.log('readdir', await fs.readdir('/'));
        await fs.trim();
        // Show discarded regions
        console.log('discarded', disk.getDiscardedChunks());
        // Show ranges of useful data aligned to 1MiB
        console.log('ranges', await disk.getRanges(1024 ** 2));
      });
    });
  } catch (error) {
    console.error(error);
  }
}

• Prerequisites

  • git
  • make
  • NodeJS >=v12

• Install emscripten

# Get the emsdk repo
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory
cd emsdk

# Download and install the latest SDK tools.
./emsdk install latest

# Make the "latest" SDK "active" for the current user. (writes .emscripten file)
./emsdk activate latest

# Activate PATH and other environment variables in the current terminal
source ./emsdk_env.sh

• Clone recursively

# You must clone recursively in order to get the dependency
git clone --recursive https://github.com/balena-io-modules/node-ext2fs

• Build

cd node-ext2fs
npm i
npm run build

If you're having any problems, please raise an issue on GitHub.

node-ext2fs is free software, and may be redistributed under the terms specified in the license.