Add "podman volume" command

Add support for podman volume and its subcommands.
The commands supported are:
	podman volume create
	podman volume inspect
	podman volume ls
	podman volume rm
	podman volume prune

This is a tool to manage volumes used by podman. For now it only handle
named volumes, but eventually it will handle all volumes used by podman.

Signed-off-by: umohnani8 <umohnani@redhat.com>

libpod/runtime_volume_linux.go

@@ -0,0 +1,132 @@
+// +build linux
+
+package libpod
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/containers/storage"
+	"github.com/containers/storage/pkg/stringid"
+	"github.com/opencontainers/selinux/go-selinux/label"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// NewVolume creates a new empty volume
+func (r *Runtime) NewVolume(ctx context.Context, options ...VolumeCreateOption) (*Volume, error) {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	if !r.valid {
+		return nil, ErrRuntimeStopped
+	}
+	return r.newVolume(ctx, options...)
+}
+
+// newVolume creates a new empty volume
+func (r *Runtime) newVolume(ctx context.Context, options ...VolumeCreateOption) (*Volume, error) {
+	volume, err := newVolume(r)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error creating volume")
+	}
+
+	for _, option := range options {
+		if err := option(volume); err != nil {
+			return nil, errors.Wrapf(err, "error running volume create option")
+		}
+	}
+
+	if volume.config.Name == "" {
+		volume.config.Name = stringid.GenerateNonCryptoID()
+	}
+	// TODO: support for other volume drivers
+	if volume.config.Driver == "" {
+		volume.config.Driver = "local"
+	}
+	// TODO: determine when the scope is global and set it to that
+	if volume.config.Scope == "" {
+		volume.config.Scope = "local"
+	}
+
+	// Create the mountpoint of this volume
+	fullVolPath := filepath.Join(r.config.VolumePath, volume.config.Name, "_data")
+	if err := os.MkdirAll(fullVolPath, 0755); err != nil {
+		return nil, errors.Wrapf(err, "error creating volume directory %q", fullVolPath)
+	}
+	_, mountLabel, err := label.InitLabels([]string{})
+	if err != nil {
+		return nil, errors.Wrapf(err, "error getting default mountlabels")
+	}
+	if err := label.ReleaseLabel(mountLabel); err != nil {
+		return nil, errors.Wrapf(err, "error releasing label %q", mountLabel)
+	}
+	if err := label.Relabel(fullVolPath, mountLabel, true); err != nil {
+		return nil, errors.Wrapf(err, "error setting selinux label to %q", fullVolPath)
+	}
+	volume.config.MountPoint = fullVolPath
+
+	// Path our lock file will reside at
+	lockPath := filepath.Join(r.lockDir, volume.config.Name)
+	// Grab a lockfile at the given path
+	lock, err := storage.GetLockfile(lockPath)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error creating lockfile for new volume")
+	}
+	volume.lock = lock
+
+	volume.valid = true
+
+	// Add the volume to state
+	if err := r.state.AddVolume(volume); err != nil {
+		return nil, errors.Wrapf(err, "error adding volume to state")
+	}
+
+	return volume, nil
+}
+
+// removeVolume removes the specified volume from state as well tears down its mountpoint and storage
+func (r *Runtime) removeVolume(ctx context.Context, v *Volume, force, prune bool) error {
+	if !v.valid {
+		return ErrNoSuchVolume
+	}
+
+	deps, err := r.state.VolumeInUse(v)
+	if err != nil {
+		return err
+	}
+	if len(deps) != 0 {
+		if prune {
+			return ErrVolumeBeingUsed
+		}
+		depsStr := strings.Join(deps, ", ")
+		if !force {
+			return errors.Wrapf(ErrVolumeBeingUsed, "volume %s is being used by the following container(s): %s", v.Name(), depsStr)
+		}
+		// If using force, log the warning that the volume is being used by at least one container
+		logrus.Warnf("volume %s is being used by the following container(s): %s", v.Name(), depsStr)
+		// Remove the container dependencies so we can go ahead and delete the volume
+		for _, dep := range deps {
+			if err := r.state.RemoveVolCtrDep(v, dep); err != nil {
+				return errors.Wrapf(err, "unable to remove container dependency %q from volume %q while trying to delete volume by force", dep, v.Name())
+			}
+		}
+	}
+
+	// Delete the mountpoint path of the volume, that is delete the volume from /var/lib/containers/storage/volumes
+	if err := v.teardownStorage(); err != nil {
+		return errors.Wrapf(err, "error cleaning up volume storage for %q", v.Name())
+	}
+
+	// Remove the volume from the state
+	if err := r.state.RemoveVolume(v); err != nil {
+		return errors.Wrapf(err, "error removing volume %s", v.Name())
+	}
+
+	// Set volume as invalid so it can no longer be used
+	v.valid = false
+
+	return nil
+}