Add NFS mount driver (#38)

* add nfs mount driver

* switch to unix.Mount for nfs mounting

* fix bad reference in nfs unmount

* fix bad reference in nfs unmount

internal/api/mount_nfs.go

@@ -0,0 +1,83 @@
+package api
+
+import (
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/bensallen/rbd/pkg/mount"
+	"github.com/kraken-hpc/imageapi/models"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
+)
+
+func init() {
+	MountDrivers[models.MountKindNfs] = &MountDriverNFS{}
+}
+
+type MountDriverNFS struct {
+	log *logrus.Entry //
+}
+
+func (m *MountDriverNFS) Init(log *logrus.Entry) {
+	m.log = log
+	m.log.Trace("initialized")
+}
+
+func (m *MountDriverNFS) Mount(mnt *Mount) (ret *Mount, err error) {
+	l := m.log.WithField("operation", "mount")
+	if mnt.Nfs == nil {
+		l.Trace("attempted nfs mount with no mount definition")
+		return nil, ERRINVALDAT
+	}
+	l = l.WithFields(logrus.Fields{
+		"host": *mnt.Nfs.Host,
+		"path": *mnt.Nfs.Path,
+	})
+	// Resolve host
+	ips, err := net.LookupIP(*mnt.Nfs.Host)
+	if err != nil {
+		l.WithError(err).Debug("host resolution failed")
+		return nil, ERRINVALDAT
+	}
+	ip := ips[0] // should we be smarter about this?
+	// ok, we're good to attempt the mount
+	// make a mountpoint
+	flags := uintptr(0)
+	if mnt.Nfs.Ro != nil && *mnt.Nfs.Ro {
+		flags = unix.MS_RDONLY
+	}
+	version := "4.2"
+	if mnt.Nfs.Version != nil {
+		version = *mnt.Nfs.Version
+	}
+	mnt.Nfs.Options = append(mnt.Nfs.Options, fmt.Sprintf("addr=%s", ip.String()))
+	mnt.Nfs.Options = append(mnt.Nfs.Options, fmt.Sprintf("clientaddr=%s", ip.String()))
+	mnt.Nfs.Options = append(mnt.Nfs.Options, fmt.Sprintf("vers=%s", version))
+	// this doesn't work because u-root Mount is broken
+	//if err = mount.Mount(fmt.Sprintf("%s:%s", *mnt.Nfs.Host, *mnt.Nfs.Path), mnt.Mountpoint, "nfs", mnt.Nfs.MountOptions); err != nil {
+	if err = unix.Mount(fmt.Sprintf("%s:%s", *mnt.Nfs.Host, *mnt.Nfs.Path), mnt.Mountpoint, "nfs", flags, strings.Join(mnt.Nfs.Options, ",")); err != nil {
+		l.WithError(err).Error("failed to mount")
+		return nil, ERRFAIL
+	}
+	l.Info("successfully mounted")
+	return mnt, nil
+}
+
+func (m *MountDriverNFS) Unmount(mnt *Mount) (ret *Mount, err error) {
+	l := m.log.WithFields(logrus.Fields{
+		"operation": "unmount",
+		"id":        mnt.ID,
+		"host":      mnt.Nfs.Host,
+		"path":      mnt.Nfs.Path,
+	})
+
+	// always lazy unmount.  Good idea?
+	if err = mount.Unmount(mnt.Mountpoint, false, true); err != nil {
+		l.WithError(err).Error("unmount failed")
+		return nil, ERRFAIL
+	}
+	l.Info("successfully unmounted")
+	// garbage collection should do our cleanup
+	return mnt, nil
+}