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.go

@@ -0,0 +1,107 @@
+package libpod
+
+import (
+	"context"
+)
+
+// Contains the public Runtime API for volumes
+
+// A VolumeCreateOption is a functional option which alters the Volume created by
+// NewVolume
+type VolumeCreateOption func(*Volume) error
+
+// VolumeFilter is a function to determine whether a volume is included in command
+// output. Volumes to be outputted are tested using the function. a true return will
+// include the volume, a false return will exclude it.
+type VolumeFilter func(*Volume) bool
+
+// RemoveVolume removes a volumes
+func (r *Runtime) RemoveVolume(ctx context.Context, v *Volume, force, prune bool) error {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	if !r.valid {
+		return ErrRuntimeStopped
+	}
+
+	if !v.valid {
+		if ok, _ := r.state.HasVolume(v.Name()); !ok {
+			// Volume probably already removed
+			// Or was never in the runtime to begin with
+			return nil
+		}
+	}
+
+	v.lock.Lock()
+	defer v.lock.Unlock()
+
+	return r.removeVolume(ctx, v, force, prune)
+}
+
+// GetVolume retrieves a volume by its name
+func (r *Runtime) GetVolume(name string) (*Volume, error) {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	if !r.valid {
+		return nil, ErrRuntimeStopped
+	}
+
+	return r.state.Volume(name)
+}
+
+// HasVolume checks to see if a volume with the given name exists
+func (r *Runtime) HasVolume(name string) (bool, error) {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	if !r.valid {
+		return false, ErrRuntimeStopped
+	}
+
+	return r.state.HasVolume(name)
+}
+
+// Volumes retrieves all volumes
+// Filters can be provided which will determine which volumes are included in the
+// output. Multiple filters are handled by ANDing their output, so only volumes
+// matching all filters are returned
+func (r *Runtime) Volumes(filters ...VolumeFilter) ([]*Volume, error) {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	if !r.valid {
+		return nil, ErrRuntimeStopped
+	}
+
+	vols, err := r.state.AllVolumes()
+	if err != nil {
+		return nil, err
+	}
+
+	volsFiltered := make([]*Volume, 0, len(vols))
+	for _, vol := range vols {
+		include := true
+		for _, filter := range filters {
+			include = include && filter(vol)
+		}
+
+		if include {
+			volsFiltered = append(volsFiltered, vol)
+		}
+	}
+
+	return volsFiltered, nil
+}
+
+// GetAllVolumes retrieves all the volumes
+func (r *Runtime) GetAllVolumes() ([]*Volume, error) {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	if !r.valid {
+		return nil, ErrRuntimeStopped
+	}
+
+	return r.state.AllVolumes()
+}