devmapper: add pool metadata
Signed-off-by: Maksym Pavlenko <makpav@amazon.com>
This commit is contained in:
Maksym Pavlenko
313
snapshots/devmapper/metadata.go
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313
snapshots/devmapper/metadata.go
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@@ -0,0 +1,313 @@
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/*
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Copyright The containerd Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package devmapper
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import (
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"context"
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"encoding/json"
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"fmt"
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"strconv"
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"github.com/pkg/errors"
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bolt "go.etcd.io/bbolt"
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)
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type (
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// DeviceInfoCallback is a callback used for device updates
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DeviceInfoCallback func(deviceInfo *DeviceInfo) error
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)
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type deviceIDState byte
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const (
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deviceFree deviceIDState = iota
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deviceTaken
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)
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// Bucket names
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var (
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devicesBucketName = []byte("devices") // Contains thin devices metadata <device_name>=<DeviceInfo>
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deviceIDBucketName = []byte("device_ids") // Tracks used device ids <device_id_[0..maxDeviceID)>=<byte_[0/1]>
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)
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var (
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// ErrNotFound represents an error returned when object not found in meta store
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ErrNotFound = errors.New("not found")
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// ErrAlreadyExists represents an error returned when object can't be duplicated in meta store
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ErrAlreadyExists = errors.New("object already exists")
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)
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// PoolMetadata keeps device info for the given thin-pool device, it also responsible for
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// generating next available device ids and tracking devmapper transaction numbers
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type PoolMetadata struct {
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db *bolt.DB
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}
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// NewPoolMetadata creates new or open existing pool metadata database
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func NewPoolMetadata(dbfile string) (*PoolMetadata, error) {
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db, err := bolt.Open(dbfile, 0600, nil)
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if err != nil {
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return nil, err
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}
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metadata := &PoolMetadata{db: db}
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if err := metadata.ensureDatabaseInitialized(); err != nil {
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return nil, errors.Wrap(err, "failed to initialize database")
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}
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return metadata, nil
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}
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// ensureDatabaseInitialized creates buckets required for metadata store in order
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// to avoid bucket existence checks across the code
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func (m *PoolMetadata) ensureDatabaseInitialized() error {
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return m.db.Update(func(tx *bolt.Tx) error {
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if _, err := tx.CreateBucketIfNotExists(devicesBucketName); err != nil {
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return err
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}
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if _, err := tx.CreateBucketIfNotExists(deviceIDBucketName); err != nil {
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return err
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}
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return nil
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})
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}
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// AddDevice saves device info to database.
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func (m *PoolMetadata) AddDevice(ctx context.Context, info *DeviceInfo) error {
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return m.db.Update(func(tx *bolt.Tx) error {
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devicesBucket := tx.Bucket(devicesBucketName)
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// Make sure device name is unique
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if err := getObject(devicesBucket, info.Name, nil); err == nil {
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return ErrAlreadyExists
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}
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// Find next available device ID
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deviceID, err := getNextDeviceID(tx)
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if err != nil {
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return err
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}
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info.DeviceID = deviceID
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return putObject(devicesBucket, info.Name, info, false)
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})
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}
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// getNextDeviceID finds the next free device ID by taking a cursor
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// through the deviceIDBucketName bucket and finding the next sequentially
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// unassigned ID. Device ID state is marked by a byte deviceFree or
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// deviceTaken. Low device IDs will be reused sooner.
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func getNextDeviceID(tx *bolt.Tx) (uint32, error) {
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bucket := tx.Bucket(deviceIDBucketName)
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cursor := bucket.Cursor()
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// Check if any device id can be reused.
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// Bolt stores its keys in byte-sorted order within a bucket.
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// This makes sequential iteration extremely fast.
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for key, taken := cursor.First(); key != nil; key, taken = cursor.Next() {
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isFree := taken[0] == byte(deviceFree)
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if !isFree {
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continue
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}
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parsedID, err := strconv.ParseUint(string(key), 10, 32)
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if err != nil {
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return 0, err
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}
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id := uint32(parsedID)
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if err := markDeviceID(tx, id, deviceTaken); err != nil {
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return 0, err
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}
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return id, nil
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}
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// Try allocate new device ID
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seq, err := bucket.NextSequence()
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if err != nil {
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return 0, err
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}
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if seq >= maxDeviceID {
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return 0, errors.Errorf("dm-meta: couldn't find free device key")
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}
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id := uint32(seq)
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if err := markDeviceID(tx, id, deviceTaken); err != nil {
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return 0, err
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}
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return id, nil
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}
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// markDeviceID marks a device as deviceFree or deviceTaken
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func markDeviceID(tx *bolt.Tx, deviceID uint32, state deviceIDState) error {
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var (
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bucket = tx.Bucket(deviceIDBucketName)
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key = strconv.FormatUint(uint64(deviceID), 10)
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value = []byte{byte(state)}
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)
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if err := bucket.Put([]byte(key), value); err != nil {
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return errors.Wrapf(err, "failed to free device id %q", key)
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}
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return nil
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}
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// UpdateDevice updates device info in metadata store.
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// The callback should be used to indicate whether device info update was successful or not.
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// An error returned from the callback will rollback the update transaction in the database.
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// Name and Device ID are not allowed to change.
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func (m *PoolMetadata) UpdateDevice(ctx context.Context, name string, fn DeviceInfoCallback) error {
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return m.db.Update(func(tx *bolt.Tx) error {
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var (
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device = &DeviceInfo{}
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bucket = tx.Bucket(devicesBucketName)
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)
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if err := getObject(bucket, name, device); err != nil {
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return err
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}
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// Don't allow changing these values, keep things in sync with devmapper
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name := device.Name
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devID := device.DeviceID
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if err := fn(device); err != nil {
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return err
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}
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if name != device.Name {
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return fmt.Errorf("failed to update device info, name didn't match: %q %q", name, device.Name)
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}
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if devID != device.DeviceID {
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return fmt.Errorf("failed to update device info, device id didn't match: %d %d", devID, device.DeviceID)
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}
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return putObject(bucket, name, device, true)
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})
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}
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// GetDevice retrieves device info by name from database
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func (m *PoolMetadata) GetDevice(ctx context.Context, name string) (*DeviceInfo, error) {
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var (
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dev DeviceInfo
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err error
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)
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err = m.db.View(func(tx *bolt.Tx) error {
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bucket := tx.Bucket(devicesBucketName)
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return getObject(bucket, name, &dev)
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})
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return &dev, err
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}
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// RemoveDevice removes device info from store.
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func (m *PoolMetadata) RemoveDevice(ctx context.Context, name string) error {
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return m.db.Update(func(tx *bolt.Tx) error {
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var (
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device = &DeviceInfo{}
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bucket = tx.Bucket(devicesBucketName)
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)
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if err := getObject(bucket, name, device); err != nil {
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return err
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}
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if err := bucket.Delete([]byte(name)); err != nil {
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return errors.Wrapf(err, "failed to delete device info for %q", name)
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}
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if err := markDeviceID(tx, device.DeviceID, deviceFree); err != nil {
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return err
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}
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return nil
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})
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}
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// GetDeviceNames retrieves the list of device names currently stored in database
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func (m *PoolMetadata) GetDeviceNames(ctx context.Context) ([]string, error) {
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var (
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names []string
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err error
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)
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err = m.db.View(func(tx *bolt.Tx) error {
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bucket := tx.Bucket(devicesBucketName)
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return bucket.ForEach(func(k, _ []byte) error {
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names = append(names, string(k))
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return nil
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})
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})
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if err != nil {
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return nil, err
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}
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return names, nil
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}
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// Close closes metadata store
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func (m *PoolMetadata) Close() error {
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if err := m.db.Close(); err != nil && err != bolt.ErrDatabaseNotOpen {
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return err
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}
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return nil
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}
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func putObject(bucket *bolt.Bucket, key string, obj interface{}, overwrite bool) error {
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keyBytes := []byte(key)
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if !overwrite && bucket.Get(keyBytes) != nil {
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return errors.Errorf("object with key %q already exists", key)
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}
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data, err := json.Marshal(obj)
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if err != nil {
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return errors.Wrapf(err, "failed to marshal object with key %q", key)
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}
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if err := bucket.Put(keyBytes, data); err != nil {
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return errors.Wrapf(err, "failed to insert object with key %q", key)
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}
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return nil
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}
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func getObject(bucket *bolt.Bucket, key string, obj interface{}) error {
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data := bucket.Get([]byte(key))
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if data == nil {
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return ErrNotFound
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}
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if obj != nil {
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if err := json.Unmarshal(data, obj); err != nil {
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return errors.Wrapf(err, "failed to unmarshal object with key %q", key)
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}
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}
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return nil
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}
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