Merge pull request #5756 from Kern--/discard-blocks

Discard blocks when removing a thin device

snapshots/devmapper/README.md

@@ -26,6 +26,7 @@ The following configuration flags are supported:
   should be the same as in `/dev/mapper/` directory
 * `base_image_size` - defines how much space to allocate when creating the base device
 * `async_remove` - flag to async remove device using snapshot GC's cleanup callback
+* `discard_blocks` - whether to discard blocks when removing a device. This is especially useful for returning disk space to the filesystem when using loopback devices.
 
 Pool name and base image size are required snapshotter parameters.
 
@@ -93,6 +94,7 @@ cat << EOF
     pool_name = "${POOL_NAME}"
     root_path = "${DATA_DIR}"
     base_image_size = "10GB"
+    discard_blocks = true
 EOF
 ```
 

snapshots/devmapper/blkdiscard/blkdiscard.go

@@ -0,0 +1,41 @@
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package blkdiscard
+
+import "os/exec"
+
+// Version returns the output of "blkdiscard --version"
+func Version() (string, error) {
+	return blkdiscard("--version")
+}
+
+// BlkDiscard discards all blocks of a device.
+// devicePath is expected to be a fully qualified path.
+// BlkDiscard expects the caller to verify that the device is not in use.
+func BlkDiscard(devicePath string) (string, error) {
+	return blkdiscard(devicePath)
+}
+
+func blkdiscard(args ...string) (string, error) {
+	output, err := exec.Command("blkdiscard", args...).CombinedOutput()
+	if err != nil {
+		return "", err
+	}
+	return string(output), nil
+}

snapshots/devmapper/config.go

@@ -43,6 +43,9 @@ type Config struct {
 
 	// Flag to async remove device using Cleanup() callback in snapshots GC
 	AsyncRemove bool `toml:"async_remove"`
+
+	// Whether to discard blocks when removing a thin device.
+	DiscardBlocks bool `toml:"discard_blocks"`
 }
 
 // LoadConfig reads devmapper configuration file from disk in TOML format

snapshots/devmapper/dmsetup/dmsetup.go

@@ -16,6 +16,8 @@
    limitations under the License.
 */
 
+// Copyright 2012-2017 Docker, Inc.
+
 package dmsetup
 
 import (
@@ -26,6 +28,7 @@ import (
 	"strconv"
 	"strings"
 
+	blkdiscard "github.com/containerd/containerd/snapshots/devmapper/blkdiscard"
 	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
 )
@@ -37,6 +40,9 @@ const (
 	SectorSize = 512
 )
 
+// ErrInUse represents an error mutating a device because it is in use elsewhere
+var ErrInUse = errors.New("device is in use")
+
 // DeviceInfo represents device info returned by "dmsetup info".
 // dmsetup(8) provides more information on each of these fields.
 type DeviceInfo struct {
@@ -345,6 +351,24 @@ func BlockDeviceSize(path string) (int64, error) {
 	return size, nil
 }
 
+// DiscardBlocks discards all blocks for the given thin device
+//  ported from https://github.com/moby/moby/blob/7b9275c0da707b030e62c96b679a976f31f929d3/pkg/devicemapper/devmapper.go#L416
+func DiscardBlocks(deviceName string) error {
+	inUse, err := isInUse(deviceName)
+	if err != nil {
+		return err
+	}
+	if inUse {
+		return ErrInUse
+	}
+	path := GetFullDevicePath(deviceName)
+	_, err = blkdiscard.BlkDiscard(path)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func dmsetup(args ...string) (string, error) {
 	data, err := exec.Command("dmsetup", args...).CombinedOutput()
 	output := string(data)
@@ -406,3 +430,14 @@ func parseDmsetupError(output string) string {
 	str = strings.ToLower(str)
 	return str
 }
+
+func isInUse(deviceName string) (bool, error) {
+	info, err := Info(deviceName)
+	if err != nil {
+		return true, err
+	}
+	if len(info) != 1 {
+		return true, errors.New("could not get device info")
+	}
+	return info[0].OpenCount != 0, nil
+}

snapshots/devmapper/dmsetup/dmsetup_test.go

@@ -83,6 +83,7 @@ func TestDMSetup(t *testing.T) {
 	t.Run("ActivateDevice", testActivateDevice)
 	t.Run("DeviceStatus", testDeviceStatus)
 	t.Run("SuspendResumeDevice", testSuspendResumeDevice)
+	t.Run("DiscardBlocks", testDiscardBlocks)
 	t.Run("RemoveDevice", testRemoveDevice)
 
 	t.Run("RemovePool", func(t *testing.T) {
@@ -169,6 +170,11 @@ func testSuspendResumeDevice(t *testing.T) {
 	assert.NilError(t, err)
 }
 
+func testDiscardBlocks(t *testing.T) {
+	err := DiscardBlocks(testDeviceName)
+	assert.NilError(t, err, "failed to discard blocks")
+}
+
 func testRemoveDevice(t *testing.T) {
 	err := RemoveDevice(testPoolName)
 	assert.Assert(t, err == unix.EBUSY, "removing thin-pool with dependencies shouldn't be allowed")

snapshots/devmapper/pool_device.go

@@ -29,6 +29,7 @@ import (
 	"golang.org/x/sys/unix"
 
 	"github.com/containerd/containerd/log"
+	blkdiscard "github.com/containerd/containerd/snapshots/devmapper/blkdiscard"
 	"github.com/containerd/containerd/snapshots/devmapper/dmsetup"
 )
 
@@ -36,6 +37,7 @@ import (
 type PoolDevice struct {
 	poolName      string
 	metadata      *PoolMetadata
+	discardBlocks bool
 }
 
 // NewPoolDevice creates new thin-pool from existing data and metadata volumes.
@@ -51,6 +53,15 @@ func NewPoolDevice(ctx context.Context, config *Config) (*PoolDevice, error) {
 
 	log.G(ctx).Infof("using dmsetup:\n%s", version)
 
+	if config.DiscardBlocks {
+		blkdiscardVersion, err := blkdiscard.Version()
+		if err != nil {
+			log.G(ctx).Error("blkdiscard is not available")
+			return nil, err
+		}
+		log.G(ctx).Infof("using blkdiscard:\n%s", blkdiscardVersion)
+	}
+
 	dbpath := filepath.Join(config.RootPath, config.PoolName+".db")
 	poolMetaStore, err := NewPoolMetadata(dbpath)
 	if err != nil {
@@ -66,6 +77,7 @@ func NewPoolDevice(ctx context.Context, config *Config) (*PoolDevice, error) {
 	poolDevice := &PoolDevice{
 		poolName:      config.PoolName,
 		metadata:      poolMetaStore,
+		discardBlocks: config.DiscardBlocks,
 	}
 
 	if err := poolDevice.ensureDeviceStates(ctx); err != nil {
@@ -422,6 +434,16 @@ func (p *PoolDevice) DeactivateDevice(ctx context.Context, deviceName string, de
 
 	if err := p.transition(ctx, deviceName, Deactivating, Deactivated, func() error {
 		return retry(ctx, func() error {
+			if !deferred && p.discardBlocks {
+				err := dmsetup.DiscardBlocks(deviceName)
+				if err != nil {
+					if err == dmsetup.ErrInUse {
+						log.G(ctx).Warnf("device %q is in use, skipping blkdiscard", deviceName)
+					} else {
+						return err
+					}
+				}
+			}
 			if err := dmsetup.RemoveDevice(deviceName, opts...); err != nil {
 				return errors.Wrap(err, "failed to deactivate device")
 			}

snapshots/devmapper/pool_device_test.go

@@ -85,6 +85,7 @@ func TestPoolDevice(t *testing.T) {
 		RootPath:           tempDir,
 		BaseImageSize:      "16mb",
 		BaseImageSizeBytes: 16 * 1024 * 1024,
+		DiscardBlocks:      true,
 	}
 
 	pool, err := NewPoolDevice(ctx, config)