lock: new lock type "file"

it is a wrapper around containers/storage file locking.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

docs/libpod.conf.5.md

@@ -27,6 +27,9 @@ libpod to manage containers.
 **cgroup_manager**=""
   Specify the CGroup Manager to use; valid values are "systemd" and "cgroupfs"
 
+**lock_type**=""
+  Specify the locking mechanism to use; valid values are "shm" and "file".  Change the default only if you are sure of what you are doing, in general "file" is useful only on platforms where cgo is not available for using the faster "shm" lock type.  You may need to run "podman system renumber" after you change the lock type.
+
 **init_path**=""
   Path to the container-init binary, which forwards signals and reaps processes within containers.  Note that the container-init binary will only be used when the `--init` for podman-create and podman-run is set.
 

libpod/lock/file/file_lock.go

@@ -0,0 +1,175 @@
+package file
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"syscall"
+
+	"github.com/containers/storage"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// FileLocks is a struct enabling POSIX lock locking in a shared memory
+// segment.
+type FileLocks struct { // nolint
+	lockPath string
+	valid    bool
+}
+
+// CreateFileLock sets up a directory containing the various lock files.
+func CreateFileLock(path string) (*FileLocks, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return nil, errors.Wrapf(syscall.EEXIST, "directory %s exists", path)
+	}
+	if err := os.MkdirAll(path, 0711); err != nil {
+		return nil, errors.Wrapf(err, "cannot create %s", path)
+	}
+
+	locks := new(FileLocks)
+	locks.lockPath = path
+	locks.valid = true
+
+	return locks, nil
+}
+
+// OpenFileLock opens an existing directory with the lock files.
+func OpenFileLock(path string) (*FileLocks, error) {
+	_, err := os.Stat(path)
+	if err != nil {
+		return nil, errors.Wrapf(err, "accessing directory %s", path)
+	}
+
+	locks := new(FileLocks)
+	locks.lockPath = path
+	locks.valid = true
+
+	return locks, nil
+}
+
+// Close closes an existing shared-memory segment.
+// The segment will be rendered unusable after closing.
+// WARNING: If you Close() while there are still locks locked, these locks may
+// fail to release, causing a program freeze.
+// Close() is only intended to be used while testing the locks.
+func (locks *FileLocks) Close() error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+	err := os.RemoveAll(locks.lockPath)
+	if err != nil {
+		return errors.Wrapf(err, "deleting directory %s", locks.lockPath)
+	}
+	return nil
+}
+
+func (locks *FileLocks) getLockPath(lck uint32) string {
+	return filepath.Join(locks.lockPath, strconv.FormatInt(int64(lck), 10))
+}
+
+// AllocateLock allocates a lock and returns the index of the lock that was allocated.
+func (locks *FileLocks) AllocateLock() (uint32, error) {
+	if !locks.valid {
+		return 0, errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+
+	id := uint32(0)
+	for ; ; id++ {
+		path := locks.getLockPath(id)
+		f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+		if err != nil {
+			if os.IsExist(err) {
+				continue
+			}
+			return 0, errors.Wrapf(err, "creating lock file")
+		}
+		f.Close()
+		break
+	}
+	return id, nil
+}
+
+// AllocateGivenLock allocates the given lock from the shared-memory
+// segment for use by a container or pod.
+// If the lock is already in use or the index is invalid an error will be
+// returned.
+func (locks *FileLocks) AllocateGivenLock(lck uint32) error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+
+	f, err := os.OpenFile(locks.getLockPath(lck), os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+	if err != nil {
+		return errors.Wrapf(err, "error creating lock %d", lck)
+	}
+	f.Close()
+
+	return nil
+}
+
+// DeallocateLock frees a lock in a shared-memory segment so it can be
+// reallocated to another container or pod.
+// The given lock must be already allocated, or an error will be returned.
+func (locks *FileLocks) DeallocateLock(lck uint32) error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+	if err := os.Remove(locks.getLockPath(lck)); err != nil {
+		return errors.Wrapf(err, "deallocating lock %d", lck)
+	}
+	return nil
+}
+
+// DeallocateAllLocks frees all locks so they can be reallocated to
+// other containers and pods.
+func (locks *FileLocks) DeallocateAllLocks() error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+	files, err := ioutil.ReadDir(locks.lockPath)
+	if err != nil {
+		return errors.Wrapf(err, "error reading directory %s", locks.lockPath)
+	}
+	var lastErr error
+	for _, f := range files {
+		p := filepath.Join(locks.lockPath, f.Name())
+		err := os.Remove(p)
+		if err != nil {
+			lastErr = err
+			logrus.Errorf("deallocating lock %s", p)
+		}
+	}
+	return lastErr
+}
+
+// LockFileLock locks the given lock.
+func (locks *FileLocks) LockFileLock(lck uint32) error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+
+	l, err := storage.GetLockfile(locks.getLockPath(lck))
+	if err != nil {
+		return errors.Wrapf(err, "error acquiring lock")
+	}
+
+	l.Lock()
+	return nil
+}
+
+// UnlockFileLock unlocks the given lock.
+func (locks *FileLocks) UnlockFileLock(lck uint32) error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+	l, err := storage.GetLockfile(locks.getLockPath(lck))
+	if err != nil {
+		return errors.Wrapf(err, "error acquiring lock")
+	}
+
+	l.Unlock()
+	return nil
+}

libpod/lock/file/file_lock_test.go

@@ -0,0 +1,74 @@
+package file
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Test that creating and destroying locks work
+func TestCreateAndDeallocate(t *testing.T) {
+	d, err := ioutil.TempDir("", "filelock")
+	assert.NoError(t, err)
+	defer os.RemoveAll(d)
+
+	l, err := OpenFileLock(filepath.Join(d, "locks"))
+	assert.Error(t, err)
+
+	l, err = CreateFileLock(filepath.Join(d, "locks"))
+	assert.NoError(t, err)
+
+	lock, err := l.AllocateLock()
+	assert.NoError(t, err)
+
+	err = l.AllocateGivenLock(lock)
+	assert.Error(t, err)
+
+	err = l.DeallocateLock(lock)
+	assert.NoError(t, err)
+
+	err = l.AllocateGivenLock(lock)
+	assert.NoError(t, err)
+
+	err = l.DeallocateAllLocks()
+	assert.NoError(t, err)
+
+	err = l.AllocateGivenLock(lock)
+	assert.NoError(t, err)
+
+	err = l.DeallocateAllLocks()
+	assert.NoError(t, err)
+}
+
+// Test that creating and destroying locks work
+func TestLockAndUnlock(t *testing.T) {
+	d, err := ioutil.TempDir("", "filelock")
+	assert.NoError(t, err)
+	defer os.RemoveAll(d)
+
+	l, err := CreateFileLock(filepath.Join(d, "locks"))
+	assert.NoError(t, err)
+
+	lock, err := l.AllocateLock()
+	assert.NoError(t, err)
+
+	err = l.LockFileLock(lock)
+	assert.NoError(t, err)
+
+	lslocks, err := exec.LookPath("lslocks")
+	if err == nil {
+		lockPath := l.getLockPath(lock)
+		out, err := exec.Command(lslocks, "--json", "-p", fmt.Sprintf("%d", os.Getpid())).CombinedOutput()
+		assert.NoError(t, err)
+
+		assert.Contains(t, string(out), lockPath)
+	}
+
+	err = l.UnlockFileLock(lock)
+	assert.NoError(t, err)
+}

libpod/lock/file_lock_manager.go

@@ -0,0 +1,110 @@
+package lock
+
+import (
+	"github.com/containers/libpod/libpod/lock/file"
+)
+
+// FileLockManager manages shared memory locks.
+type FileLockManager struct {
+	locks *file.FileLocks
+}
+
+// NewFileLockManager makes a new FileLockManager at the specified directory.
+func NewFileLockManager(lockPath string) (Manager, error) {
+	locks, err := file.CreateFileLock(lockPath)
+	if err != nil {
+		return nil, err
+	}
+
+	manager := new(FileLockManager)
+	manager.locks = locks
+
+	return manager, nil
+}
+
+// OpenFileLockManager opens an existing FileLockManager at the specified directory.
+func OpenFileLockManager(path string) (Manager, error) {
+	locks, err := file.OpenFileLock(path)
+	if err != nil {
+		return nil, err
+	}
+
+	manager := new(FileLockManager)
+	manager.locks = locks
+
+	return manager, nil
+}
+
+// AllocateLock allocates a new lock from the manager.
+func (m *FileLockManager) AllocateLock() (Locker, error) {
+	semIndex, err := m.locks.AllocateLock()
+	if err != nil {
+		return nil, err
+	}
+
+	lock := new(FileLock)
+	lock.lockID = semIndex
+	lock.manager = m
+
+	return lock, nil
+}
+
+// AllocateAndRetrieveLock allocates the lock with the given ID and returns it.
+// If the lock is already allocated, error.
+func (m *FileLockManager) AllocateAndRetrieveLock(id uint32) (Locker, error) {
+	lock := new(FileLock)
+	lock.lockID = id
+	lock.manager = m
+
+	if err := m.locks.AllocateGivenLock(id); err != nil {
+		return nil, err
+	}
+
+	return lock, nil
+}
+
+// RetrieveLock retrieves a lock from the manager given its ID.
+func (m *FileLockManager) RetrieveLock(id uint32) (Locker, error) {
+	lock := new(FileLock)
+	lock.lockID = id
+	lock.manager = m
+
+	return lock, nil
+}
+
+// FreeAllLocks frees all locks in the manager.
+// This function is DANGEROUS. Please read the full comment in locks.go before
+// trying to use it.
+func (m *FileLockManager) FreeAllLocks() error {
+	return m.locks.DeallocateAllLocks()
+}
+
+// FileLock is an individual shared memory lock.
+type FileLock struct {
+	lockID  uint32
+	manager *FileLockManager
+}
+
+// ID returns the ID of the lock.
+func (l *FileLock) ID() uint32 {
+	return l.lockID
+}
+
+// Lock acquires the lock.
+func (l *FileLock) Lock() {
+	if err := l.manager.locks.LockFileLock(l.lockID); err != nil {
+		panic(err.Error())
+	}
+}
+
+// Unlock releases the lock.
+func (l *FileLock) Unlock() {
+	if err := l.manager.locks.UnlockFileLock(l.lockID); err != nil {
+		panic(err.Error())
+	}
+}
+
+// Free releases the lock, allowing it to be reused.
+func (l *FileLock) Free() error {
+	return l.manager.locks.DeallocateLock(l.lockID)
+}

libpod/runtime.go

@@ -318,6 +318,7 @@ func defaultRuntimeConfig() (RuntimeConfig, error) {
 		NumLocks:              2048,
 		EventsLogger:          events.DefaultEventerType.String(),
 		DetachKeys:            DefaultDetachKeys,
+		LockType:              "shm",
 	}, nil
 }
 
@@ -664,6 +665,20 @@ func getLockManager(runtime *Runtime) (lock.Manager, error) {
 	var manager lock.Manager
 
 	switch runtime.config.LockType {
+	case "file":
+		lockPath := filepath.Join(runtime.config.TmpDir, "locks")
+		manager, err = lock.OpenFileLockManager(lockPath)
+		if err != nil {
+			if os.IsNotExist(errors.Cause(err)) {
+				manager, err = lock.NewFileLockManager(lockPath)
+				if err != nil {
+					return nil, errors.Wrapf(err, "failed to get new file lock manager")
+				}
+			} else {
+				return nil, err
+			}
+		}
+
 	case "", "shm":
 		lockPath := DefaultSHMLockPath
 		if rootless.IsRootless() {