vfs: introduce --atime-mode option to control atime update behavior

Currently juicefs doesn't update atime on access, so introduce
--atime-mode option to select how to update atime. And support three
modes:

- noatime: don't update atime
- relatime: update atime relative to motify or change time
- strictatime: always update atime

Fixes: #3240
Signed-off-by: Eryu Guan <[email protected]>

cmd/flags.go

@@ -214,6 +214,10 @@ func clientFlags() []cli.Flag {
 			Name:  "subdir",
 			Usage: "mount a sub-directory as root",
 		},
+		&cli.StringFlag{
+			Name:  "atime-mode",
+			Usage: "when to update atime, supported mode includes: noatime (default), relatime, strictatime",
+		},
 	}
 }
 

cmd/mount.go

@@ -358,6 +358,13 @@ func getMetaConf(c *cli.Context, mp string, readOnly bool) *meta.Config {
 	conf.Heartbeat = duration(c.String("heartbeat"))
 	conf.MountPoint = mp
 	conf.Subdir = c.String("subdir")
+
+	atimeMode := c.String("atime-mode")
+	if atimeMode != meta.RelAtime && atimeMode != meta.StrictAtime {
+		logger.Warnf("unknown atime-mode \"%s\", changed to %s", atimeMode, meta.NoAtime)
+		atimeMode = meta.NoAtime
+	}
+	conf.AtimeMode = atimeMode
 	return conf
 }
 

docs/en/development/internals.md

@@ -173,7 +173,10 @@ type Attr struct {
 
 There are a few fields that need clarification.
 
-- Atime/Atimensec: set only when the file is created and when `SetAttr` is actively called, while accessing and modifying the file usually does not affect the Atime value
+- Atime/Atimensec: currently support three modes
+  - noatime: set only when the file is created and when `SetAttr` is actively called, while accessing and modifying the file usually does not affect the Atime value, this is the default behavior
+  - relatime: update  inode access times relative to modify or change time.  Access time is only updated if the previous access time was earlier than the current modify or change time, or the file's last access time is always updated if it  is more than 1 day old
+  - strictatime: always update atime on access
 - Nlink
   - Directory file: initial value is 2 ('.' and '..'), add 1 for each subdirectory
   - Other files: initial value is 1, add 1 for each hard link created

docs/en/reference/command_reference.md

@@ -318,6 +318,9 @@ interval (in seconds) to send heartbeat; it's recommended that all clients use t
 `--no-bgjob`<br />
 disable background jobs (clean-up, backup, etc.) (default: false)
 
+`--atime-mode value`<br />
+control atime behavior, support 3 modes, `noatime`, `relatime`, `strictatime`, default to `noatime`
+
 #### Examples
 
 ```bash

docs/zh_cn/development/internals.md

@@ -176,7 +176,10 @@ type Attr struct {
 
 其中几个需要说明的字段：
 
-- Atime/Atimensec：仅在文件创建和主动调用 `SetAttr` 时设置，平时访问与修改文件不影响 Atime 值
+- Atime/Atimensec：目前支持三种模式
+  - noatime: 仅在文件创建和主动调用 `SetAttr` 时设置，平时访问与修改文件不影响 Atime 值，这是默认行为
+  - relatime: Mtime 或者 Ctime 比 Atime 新时，或者 Atime 超过 24 小时没有更新时更新 Atime
+  - strictatime: 一直更新 Atime
 - Nlink：
   - 目录文件：初始值为 2（'.' 和 '..'），每有一个子目录 Nlink 值加 1
   - 其他文件：初始值为 1，每创建一个硬链接 Nlink 值加 1

docs/zh_cn/reference/command_reference.md

@@ -318,6 +318,9 @@ Consul 注册中心地址 (默认："127.0.0.1:8500")
 `--no-bgjob`<br />
 禁用后台作业（清理、备份等）（默认：false）
 
+`--atime-mode value`<br />
+控制如何更新 atime，支持3种模式，`noatime`，`relatime`，`strictatime`，默认使用 `noatime`
+
 #### 示例
 
 ```shell

pkg/meta/base.go

@@ -107,6 +107,7 @@ type engine interface {
 	scanPendingFiles(Context, pendingFileScan) error
 
 	GetSession(sid uint64, detail bool) (*Session, error)
+	touchAtime(ctx Context, inode Ino) syscall.Errno
 }
 
 type trashSliceScan func(ss []Slice, ts int64) (clean bool, err error)
@@ -1561,7 +1562,14 @@ func (m *baseMeta) Close(ctx Context, inode Ino) syscall.Errno {
 	return 0
 }
 
-func (m *baseMeta) Readdir(ctx Context, inode Ino, plus uint8, entries *[]*Entry) syscall.Errno {
+func (m *baseMeta) Readdir(ctx Context, inode Ino, plus uint8, entries *[]*Entry) (rerr syscall.Errno) {
+	defer func() {
+		if rerr == 0 {
+			if err := m.en.touchAtime(ctx, inode); err != 0 {
+				logger.Warnf("readdir %v update atime: %s", inode, err)
+			}
+		}
+	}()
 	inode = m.checkRoot(inode)
 	var attr Attr
 	if err := m.GetAttr(ctx, inode, &attr); err != 0 {

pkg/meta/config.go

@@ -44,6 +44,7 @@ type Config struct {
 	Heartbeat      time.Duration
 	MountPoint     string
 	Subdir         string
+	AtimeMode      string
 }
 
 func DefaultConf() *Config {

pkg/meta/redis.go

@@ -2113,7 +2113,14 @@ func (m *redisMeta) doDeleteSustainedInode(sid uint64, inode Ino) error {
 	return err
 }
 
-func (m *redisMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) syscall.Errno {
+func (m *redisMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) (rerr syscall.Errno) {
+	defer func() {
+		if rerr == 0 {
+			if err := m.touchAtime(ctx, inode); err != 0 {
+				logger.Warnf("read %v update atime: %s", inode, err)
+			}
+		}
+	}()
 	f := m.of.find(inode)
 	if f != nil {
 		f.RLock()
@@ -4240,3 +4247,31 @@ func (m *redisMeta) doAttachDirNode(ctx Context, parent Ino, dstIno Ino, name st
 		return err
 	}, m.inodeKey(parent), m.entryKey(parent)))
 }
+
+// caller makes sure inode is not special inode.
+func (m *redisMeta) touchAtime(ctx Context, ino Ino) syscall.Errno {
+	if (m.conf.AtimeMode != StrictAtime && m.conf.AtimeMode != RelAtime) || m.conf.ReadOnly {
+		return 0
+	}
+
+	return errno(m.txn(ctx, func(tx *redis.Tx) error {
+		var attr Attr
+		a, err := tx.Get(ctx, m.inodeKey(ino)).Bytes()
+		if err != nil {
+			return err
+		}
+		m.parseAttr(a, &attr)
+
+		now := time.Now()
+		if !m.atimeNeedsUpdate(&attr, now) {
+			return nil
+		}
+		attr.Atime = now.Unix()
+		attr.Atimensec = uint32(now.Nanosecond())
+		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
+			pipe.Set(ctx, m.inodeKey(ino), m.marshal(&attr), 0)
+			return nil
+		})
+		return err
+	}, m.inodeKey(ino)))
+}

pkg/meta/sql.go

@@ -2062,7 +2062,14 @@ func (m *dbMeta) doDeleteSustainedInode(sid uint64, inode Ino) error {
 	return err
 }
 
-func (m *dbMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) syscall.Errno {
+func (m *dbMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) (rerr syscall.Errno) {
+	defer func() {
+		if rerr == 0 {
+			if err := m.touchAtime(ctx, inode); err != 0 {
+				logger.Warnf("read %v update atime: %s", inode, err)
+			}
+		}
+	}()
 	f := m.of.find(inode)
 	if f != nil {
 		f.RLock()
@@ -3900,3 +3907,30 @@ func (m *dbMeta) doAttachDirNode(ctx Context, parent Ino, inode Ino, name string
 		return err
 	}, parent))
 }
+
+func (m *dbMeta) touchAtime(ctx Context, ino Ino) syscall.Errno {
+	if (m.conf.AtimeMode != StrictAtime && m.conf.AtimeMode != RelAtime) || m.conf.ReadOnly {
+		return 0
+	}
+
+	return errno(m.txn(func(s *xorm.Session) error {
+		var cur = node{Inode: ino}
+		var attr = Attr{}
+		ok, err := s.ForUpdate().Get(&cur)
+		if err != nil {
+			return err
+		}
+		if !ok {
+			return syscall.ENOENT
+		}
+
+		now := time.Now()
+		m.parseAttr(&cur, &attr)
+		if !m.atimeNeedsUpdate(&attr, now) {
+			return nil
+		}
+		cur.Atime = now.Unix()*1e6 + int64(now.Nanosecond())/1e3
+		_, err = s.Cols("flags", "mode", "uid", "gid", "atime", "mtime", "ctime").Update(&cur, &node{Inode: ino})
+		return err
+	}))
+}

pkg/meta/tkv.go

@@ -1816,7 +1816,14 @@ func (m *kvMeta) doDeleteSustainedInode(sid uint64, inode Ino) error {
 	return err
 }
 
-func (m *kvMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) syscall.Errno {
+func (m *kvMeta) Read(ctx Context, inode Ino, indx uint32, slices *[]Slice) (rerr syscall.Errno) {
+	defer func() {
+		if rerr == 0 {
+			if err := m.touchAtime(ctx, inode); err != 0 {
+				logger.Warnf("read %v update atime: %s", inode, err)
+			}
+		}
+	}()
 	f := m.of.find(inode)
 	if f != nil {
 		f.RLock()
@@ -3380,3 +3387,27 @@ func (m *kvMeta) doAttachDirNode(ctx Context, parent Ino, inode Ino, name string
 		return nil
 	}, parent))
 }
+
+func (m *kvMeta) touchAtime(_ctx Context, ino Ino) syscall.Errno {
+	if (m.conf.AtimeMode != StrictAtime && m.conf.AtimeMode != RelAtime) || m.conf.ReadOnly {
+		return 0
+	}
+
+	return errno(m.txn(func(tx *kvTxn) error {
+		var attr Attr
+		a := tx.get(m.inodeKey(ino))
+		if a == nil {
+			return syscall.ENOENT
+		}
+		m.parseAttr(a, &attr)
+
+		now := time.Now()
+		if !m.atimeNeedsUpdate(&attr, now) {
+			return nil
+		}
+		attr.Atime = now.Unix()
+		attr.Atimensec = uint32(now.Nanosecond())
+		tx.set(m.inodeKey(ino), m.marshal(&attr))
+		return nil
+	}))
+}

pkg/meta/utils.go

@@ -53,6 +53,11 @@ const (
 	CLONE_MODE_CAN_OVERWRITE      = 0x01
 	CLONE_MODE_PRESERVE_ATTR      = 0x02
 	CLONE_MODE_PRESERVE_HARDLINKS = 0x08
+
+	// atime mode
+	NoAtime     = "noatime"
+	RelAtime    = "relatime"
+	StrictAtime = "strictatime"
 )
 
 type msgCallbacks struct {
@@ -553,3 +558,34 @@ func (m *baseMeta) getTreeSummary(ctx Context, tree *TreeSummary, depth, topN ui
 	}
 	return 0
 }
+
+func (m *baseMeta) atimeNeedsUpdate(attr *Attr, now time.Time) bool {
+	if m.conf.AtimeMode == RelAtime && relatimeNeedUpdate(attr, now) {
+		return true
+	}
+
+	return m.conf.AtimeMode == StrictAtime && !now.Equal(time.Unix(attr.Atime, int64(attr.Atimensec)))
+}
+
+// With relative atime, only update atime if the previous atime is earlier than either the ctime or
+// mtime or if at least a day has passed since the last atime update.
+func relatimeNeedUpdate(attr *Attr, now time.Time) bool {
+	atime := time.Unix(attr.Atime, int64(attr.Atimensec))
+
+	// Is mtime younger than atime? If yes, update atime
+	if time.Unix(attr.Mtime, int64(attr.Mtimensec)).After(atime) {
+		return true
+	}
+
+	// Is ctime younger than atime? If yes, update atime
+	if time.Unix(attr.Ctime, int64(attr.Ctimensec)).After(atime) {
+		return true
+	}
+
+	// Is the previous atime value older than a day? If yes, update atime
+	if now.Sub(atime) > 24*time.Hour {
+		return true
+	}
+
+	return false
+}

pkg/meta/utils_test.go

@@ -0,0 +1,81 @@
+/*
+ * JuiceFS, Copyright 2023 Juicedata, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package meta
+
+import (
+	"testing"
+	"time"
+)
+
+func TestRelatimeNeedUpdate(t *testing.T) {
+	attr := &Attr{
+		Atime: 1000,
+	}
+	if !relatimeNeedUpdate(attr, time.Now()) {
+		t.Fatal("atime not updated for 24 hours")
+	}
+
+	now := time.Now()
+	attr.Atime = now.Unix()
+	attr.Ctime = now.Unix() + 10
+	if !relatimeNeedUpdate(attr, time.Now()) {
+		t.Fatal("atime not updated for ctime")
+	}
+
+	now = time.Now()
+	attr.Atime = now.Unix()
+	attr.Mtime = now.Unix() + 10
+	if !relatimeNeedUpdate(attr, time.Now()) {
+		t.Fatal("atime not updated for mtime")
+	}
+
+	now = time.Now()
+	attr.Atime = now.Unix()
+	attr.Mtime = now.Unix()
+	attr.Ctime = now.Unix()
+	if relatimeNeedUpdate(attr, now) {
+		t.Fatal("atime should not be updated")
+	}
+}
+
+func TestAtimeNeedsUpdate(t *testing.T) {
+	m := &baseMeta{
+		conf: &Config{
+			AtimeMode: NoAtime,
+		},
+	}
+	attr := &Attr{
+		Atime: 1000,
+	}
+	if m.atimeNeedsUpdate(attr, time.Now()) {
+		t.Fatal("atime updated for noatime")
+	}
+
+	m.conf.AtimeMode = RelAtime
+	if !m.atimeNeedsUpdate(attr, time.Now()) {
+		t.Fatal("atime not updated for relatime")
+	}
+	attr.Atime = time.Now().Unix()
+	if m.atimeNeedsUpdate(attr, time.Now()) {
+		t.Fatal("atime updated for relatime")
+	}
+
+	m.conf.AtimeMode = StrictAtime
+	if !m.atimeNeedsUpdate(attr, time.Now()) {
+		t.Fatal("atime not updated for strictatime")
+	}
+}