Add parameter to specify checkpoint archive compression

The checkpoint archive compression was hardcoded to `archive.Gzip`.

There have been requests to make the used compression algorithm
selectable. There was especially the request to not compress the
checkpoint archive to be able to create faster checkpoints when not
compressing it.

This also changes the default from `gzip` to `zstd`. This change should
not break anything as the restore code path automatically handles
whatever compression the user provides during restore.

Signed-off-by: Adrian Reber <areber@redhat.com>

cmd/podman/common/completion.go

@@ -1211,3 +1211,10 @@ func AutocompleteVolumeFilters(cmd *cobra.Command, args []string, toComplete str
 	}
 	return completeKeyValues(toComplete, kv)
 }
+
+// AutocompleteCheckpointCompressType - Autocomplete checkpoint compress type options.
+// -> "gzip", "none", "zstd"
+func AutocompleteCheckpointCompressType(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	types := []string{"gzip", "none", "zstd"}
+	return types, cobra.ShellCompDirectiveNoFileComp
+}

cmd/podman/containers/checkpoint.go

@@ -3,6 +3,7 @@ package containers
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/containers/common/pkg/completion"
 	"github.com/containers/podman/v3/cmd/podman/common"
@@ -11,6 +12,7 @@ import (
 	"github.com/containers/podman/v3/cmd/podman/validate"
 	"github.com/containers/podman/v3/pkg/domain/entities"
 	"github.com/containers/podman/v3/pkg/rootless"
+	"github.com/containers/storage/pkg/archive"
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 )
@@ -36,9 +38,7 @@ var (
 	}
 )
 
-var (
-	checkpointOptions entities.CheckpointOptions
-)
+var checkpointOptions entities.CheckpointOptions
 
 func init() {
 	registry.Commands = append(registry.Commands, registry.CliCommand{
@@ -60,11 +60,32 @@ func init() {
 	flags.BoolVarP(&checkpointOptions.PreCheckPoint, "pre-checkpoint", "P", false, "Dump container's memory information only, leave the container running")
 	flags.BoolVar(&checkpointOptions.WithPrevious, "with-previous", false, "Checkpoint container with pre-checkpoint images")
 
+	flags.StringP("compress", "c", "zstd", "Select compression algorithm (gzip, none, zstd) for checkpoint archive.")
+	_ = checkpointCommand.RegisterFlagCompletionFunc("compress", common.AutocompleteCheckpointCompressType)
+
 	validate.AddLatestFlag(checkpointCommand, &checkpointOptions.Latest)
 }
 
 func checkpoint(cmd *cobra.Command, args []string) error {
 	var errs utils.OutputErrors
+	if cmd.Flags().Changed("compress") {
+		if checkpointOptions.Export == "" {
+			return errors.Errorf("--compress can only be used with --export")
+		}
+		compress, _ := cmd.Flags().GetString("compress")
+		switch strings.ToLower(compress) {
+		case "none":
+			checkpointOptions.Compression = archive.Uncompressed
+		case "gzip":
+			checkpointOptions.Compression = archive.Gzip
+		case "zstd":
+			checkpointOptions.Compression = archive.Zstd
+		default:
+			return errors.Errorf("Selected compression algorithm (%q) not supported. Please select one from: gzip, none, zstd", compress)
+		}
+	} else {
+		checkpointOptions.Compression = archive.Zstd
+	}
 	if rootless.IsRootless() {
 		return errors.New("checkpointing a container requires root")
 	}

libpod/container_api.go

@@ -12,6 +12,7 @@ import (
 	"github.com/containers/podman/v3/libpod/define"
 	"github.com/containers/podman/v3/libpod/events"
 	"github.com/containers/podman/v3/pkg/signal"
+	"github.com/containers/storage/pkg/archive"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -776,6 +777,9 @@ type ContainerCheckpointOptions struct {
 	// ImportPrevious tells the API to restore container with two
 	// images. One is TargetFile, the other is ImportPrevious.
 	ImportPrevious string
+	// Compression tells the API which compression to use for
+	// the exported checkpoint archive.
+	Compression archive.Compression
 }
 
 // Checkpoint checkpoints a container

libpod/container_internal_linux.go

@@ -985,7 +985,7 @@ func (c *Container) exportCheckpoint(options ContainerCheckpointOptions) error {
 	}
 
 	input, err := archive.TarWithOptions(c.bundlePath(), &archive.TarOptions{
-		Compression:      archive.Gzip,
+		Compression:      options.Compression,
 		IncludeSourceDir: true,
 		IncludeFiles:     includeFiles,
 	})

pkg/domain/entities/containers.go

@@ -9,6 +9,7 @@ import (
 	"github.com/containers/image/v5/types"
 	"github.com/containers/podman/v3/libpod/define"
 	"github.com/containers/podman/v3/pkg/specgen"
+	"github.com/containers/storage/pkg/archive"
 	"github.com/cri-o/ocicni/pkg/ocicni"
 )
 
@@ -178,6 +179,7 @@ type CheckpointOptions struct {
 	TCPEstablished bool
 	PreCheckPoint  bool
 	WithPrevious   bool
+	Compression    archive.Compression
 }
 
 type CheckpointReport struct {

pkg/domain/infra/abi/containers.go

@@ -483,6 +483,7 @@ func (ic *ContainerEngine) ContainerCheckpoint(ctx context.Context, namesOrIds [
 		KeepRunning:    options.LeaveRunning,
 		PreCheckPoint:  options.PreCheckPoint,
 		WithPrevious:   options.WithPrevious,
+		Compression:    options.Compression,
 	}
 
 	if options.All {