volumes: Add support for exporting volumes to external tar

Adds support for transferring data between systems and backing up systems.
Use cases: recover from disasters or move data between machines.

Signed-off-by: flouthoc <flouthoc.git@gmail.com>

1 files changed, 96 insertions, 0 deletions

diff --git a/cmd/podman/volumes/export.go b/cmd/podman/volumes/export.go
new file mode 100644
index 000000000..9e4fecdfa
--- /dev/null
+++ b/cmd/podman/volumes/export.go
@@ -0,0 +1,96 @@
+package volumes
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/containers/common/pkg/completion"
+	"github.com/containers/podman/v3/cmd/podman/common"
+	"github.com/containers/podman/v3/cmd/podman/inspect"
+	"github.com/containers/podman/v3/cmd/podman/registry"
+	"github.com/containers/podman/v3/pkg/domain/entities"
+	"github.com/containers/podman/v3/utils"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+var (
+	volumeExportDescription = `
+podman volume export
+
+Allow content of volume to be exported into external tar.`
+	exportCommand = &cobra.Command{
+		Annotations:       map[string]string{registry.EngineMode: registry.ABIMode},
+		Use:               "export [options] VOLUME",
+		Short:             "Export volumes",
+		Args:              cobra.ExactArgs(1),
+		Long:              volumeExportDescription,
+		RunE:              export,
+		ValidArgsFunction: common.AutocompleteVolumes,
+	}
+)
+
+var (
+	// Temporary struct to hold cli values.
+	cliExportOpts = struct {
+		Output string
+	}{}
+)
+
+func init() {
+	registry.Commands = append(registry.Commands, registry.CliCommand{
+		Command: exportCommand,
+		Parent:  volumeCmd,
+	})
+	flags := exportCommand.Flags()
+
+	outputFlagName := "output"
+	flags.StringVarP(&cliExportOpts.Output, outputFlagName, "o", "/dev/stdout", "Write to a specified file (default: stdout, which must be redirected)")
+	_ = exportCommand.RegisterFlagCompletionFunc(outputFlagName, completion.AutocompleteDefault)
+}
+
+func export(cmd *cobra.Command, args []string) error {
+	var inspectOpts entities.InspectOptions
+	containerEngine := registry.ContainerEngine()
+	ctx := context.Background()
+
+	if cliExportOpts.Output == "" {
+		return errors.New("expects output path, use --output=[path]")
+	}
+	inspectOpts.Type = inspect.VolumeType
+	volumeData, _, err := containerEngine.VolumeInspect(ctx, args, inspectOpts)
+	if err != nil {
+		return err
+	}
+	if len(volumeData) < 1 {
+		return errors.New("no volume data found")
+	}
+	mountPoint := volumeData[0].VolumeConfigResponse.Mountpoint
+	driver := volumeData[0].VolumeConfigResponse.Driver
+	volumeOptions := volumeData[0].VolumeConfigResponse.Options
+	volumeMountStatus, err := containerEngine.VolumeMounted(ctx, args[0])
+	if err != nil {
+		return err
+	}
+	if mountPoint == "" {
+		return errors.New("volume is not mounted anywhere on host")
+	}
+	// Check if volume is using external plugin and export only if volume is mounted
+	if driver != "" && driver != "local" {
+		if !volumeMountStatus.Value {
+			return fmt.Errorf("volume is using a driver %s and volume is not mounted on %s", driver, mountPoint)
+		}
+	}
+	// Check if volume is using `local` driver and has mount options type other than tmpfs
+	if driver == "local" {
+		if mountOptionType, ok := volumeOptions["type"]; ok {
+			if mountOptionType != "tmpfs" && !volumeMountStatus.Value {
+				return fmt.Errorf("volume is using a driver %s and volume is not mounted on %s", driver, mountPoint)
+			}
+		}
+	}
+	logrus.Debugf("Exporting volume data from %s to %s", mountPoint, cliExportOpts.Output)
+	err = utils.CreateTarFromSrc(mountPoint, cliExportOpts.Output)
+	return err
+}