btrsync

A library and tool for working with btrfs filesystems and snapshots in Golang.

Features

Beyond the native (no CGO*) bindings for working with BTRFS file systems provided in pkg, the btrsync utility included has the following features:

• Manage and sync snapshots to local and remote locations
• Mirror to compressed files as well as both btrfs and non-btrfs volumes
• Automatic volume and subvolume discovery for easy config generation
• Recovery of interrupted transfers by natively scanning the btrfs send streams and tracking offsets
• Mount a btrfs sendfile as an in-memory FUSE filesystem (incremental sendfiles not supported yet)

Btrsync can be run either as a daemon process, cron job, or from the command line. It will manage snapshots and their mirrors according to its configuration or command line flags.

*Cgo is used to generate certain constants and structures in the codebase, but not at compile time

Ideas in the pipeline:

[ ] S3 Support

Command Usage

Pre-compiled binaries for Linux can be found under the releases.

Documentation on the btrsync utility can be found in docs/. An example of the configuration format can be found in btrsync.example.toml.

Library Usage

For comprehensive usage of the bindings, see the go.dev. But below are overviews of some common operations:

Volumes

Volume-wide bindings (such as interacting with RAID levels) are basically non-existant at the moment, but more will potentially come.

package main

import (
	"fmt"
	"path/filepath"

	"github.com/tinyzimmer/btrsync/pkg/btrfs"
)

func main() {
	// List all mounted Btrfs paths
	mounts, err := btrfs.ListBtrfsMounts()
	if err != nil {
		panic(err)
	}
	for _, mount := range mounts {
		fmt.Println(mount.Device) // The device the filesystem is on
		isBtrfs, err := btrfs.IsBtrfs(mount.Path)
		fmt.Println(isBtrfs, err) // Would print true for all mounts

		path := filepath.Join(mount.Path, "some-directory")
		root, err := btrfs.FindRootMount(path)
		fmt.Println(root, err) // Would print the mount itself

		// Get usage information about the device
		info, err := btrfs.GetDeviceInfo(root.Path) // or root.DeviceInfo()
		fmt.Println(info, err)

		// Get statistics about the device
		stats, err := btrfs.GetDeviceStats(root.Path) // or root.DeviceStats()
		fmt.Println(stats, err)
	}
}

Subvolumes

package main

import (
	"fmt"

	"github.com/tinyzimmer/btrsync/pkg/btrfs"
)

func main() {
	// Create a subvolume
	err := btrfs.CreateSubvolume("/mnt/btrfs/subvol")
	if err != nil {
		panic(err)
	}
	fmt.Println(btrfs.IsSubvolume("/mnt/btrfs/subvol")) // true
	// Retrieve information about the subvolume. See docs for other search options.
	info, err := btrfs.SubvolumeSearch(btrfs.SearchWithPath("/mnt/btrfs/subvol"))
	if err != nil {
		panic(err)
	}
	fmt.Println(info)

	// Make the subvolume read-only
	err = btrfs.SetSubvolumeReadOnly("/mnt/btrfs/subvol")
	if err != nil {
		panic(err)
	}

	// Try to delete the subvolume
	err = btrfs.DeleteSubvolume("/mnt/btrfs/subvol", false)
	fmt.Println(err) // fails: subvolume is read-only
	// Force delete removes read-only flag
	err = btrfs.DeleteSubvolume("/mnt/btrfs/subvol", true)
	if err != nil {
		panic(err)
	}

	// Build a red-black tree of a volume or subvolume
	tree, err := btrfs.BuildRBTree("/mnt/btrfs")
	if err != nil {
		panic(err)
	}

	// Iterate the tree in-order
	tree.InOrderIterate(func(info *btrfs.RootInfo, lastErr error) error {
		fmt.Println(info.UUID)
		return nil
	})
}

Snapshots

package main

import (
	"fmt"

	"github.com/tinyzimmer/btrsync/pkg/btrfs"
)

func main() {
	// Create a snapshot at /mnt/btrfs/subvol/snapshot
	err := btrfs.CreateSnapshot("/mnt/btrfs/subvol", btrfs.WithSnapshotName("snapshot"))
	if err != nil { 
		return err 
	}
	// Create a snapshot using the full path to the snapshot (must reside on the same BTRFS volume)
	err = btrfs.CreateSnapshot("/mnt/btrfs/subvol", btrfs.WithSnapshotPath("/mnt/btrfs/subvol/snapshots/snapshot-1"))
	if err != nil { 
		return err 
	}
	// Delete a snapshot
	err = btrfs.DeleteSnapshot("/mnt/btrfs/subvol/snapshots/snapshot-1")
	if err != nil {
		panic(err)
	}
}

Sending/Receiving

The sendstream package implements the btrfs send/receive write format in pure Go. Streams can be constructed and read to raw using the package, or directly via the btrfs ioctls in the btrfs package.

Sending directly from a btrfs subvolume is done from the btrfs package while receiving methods are in the receive package. The receivers subpackage contains different implementations of "Receivers" that can be invoked for each command encountered in a stream. Receivers are just interfaces that expose methods for each command encountered, and custom ones can be made and used.

package main

import (
	"fmt"

	"github.com/tinyzimmer/btrsync/pkg/btrfs"
	"github.com/tinyzimmer/btrsync/pkg/receive"
	"github.com/tinyzimmer/btrsync/pkg/receive/receivers/local"
)

func main() {
	// First create a read-only snapshot for sending
	err := btrfs.CreateSnapshot("/mnt/btrfs/subvol", 
		btrfs.WithReadOnlySnapshot(),
		btrfs.WithSnapshotPath("/mnt/btrfs/subvol/snapshots/snapshot-1"))
	if err != nil { 
		panic(err)
	}

	// There are many options for where and how to send the data. 
	// Below is an example of sending it directly to a pipe with encoded writes where applicable
	pipeOpt, sendPipe, err := btrfs.SendToPipe()
	if err != nil {
		panic(err)
	}
	// Start the send in a goroutine
	var wg sync.WaitGroup
	errs := make(chan error, 1)
	wg.Add(1)
	go func() {
		defer wg.Done()
		errs <- btrfs.Send(
			"/mnt/btrfs/subvol/snapshots/snapshot-1", 
			pipeOpt, btrfs.SendCompressedData())
	}()

	// We can receive directly from the pipe above, in this example to another local btrfs volume
	err = btrfs.ProcessSendStream(sendPipe, 
		receive.HonorEndCommand(),
		receive.To(local.New("/mnt/btrfs-2/subvol"))
	)
	if err != nil {
		panic(err)
	}

	// The above will block until the stream errors or finishes, 
	// but we can use a wait group to be safe anyway or if we wanted to
	// also run the receive in a goroutine.
	wg.Wait()
	close(errs)
	for _, err := range errs {
		if err != nil {
			panic(err)
		}
	}
}

Contributing

PRs are welcome! Feel free to open issues for found bugs, but for simple addition of an ioctl or two it would be preferable to open a PR. Also, feel free to open issues for feature and/or bug discussions about the btrsync and btrtm utilities.