Implement setattr+clunk in 9P

This is to cover the common pattern: open->read/write->close,
where SetAttr needs to be called to update atime/mtime before
the file is closed.

Benchmark results:

BM_OpenReadClose/10240 CPU
setattr+clunk: 63783 ns
VFS2:          68109 ns
VFS1:          72507 ns

Updates #1198

PiperOrigin-RevId: 329628461

8 files changed, 280 insertions, 90 deletions

diff --git a/pkg/p9/client_file.go b/pkg/p9/client_file.go
index 2ee07b664..28fe081d6 100644
--- a/pkg/p9/client_file.go
+++ b/pkg/p9/client_file.go
@@ -54,6 +54,8 @@ func (c *Client) newFile(fid FID) *clientFile {
 //
 // This proxies all of the interfaces found in file.go.
 type clientFile struct {
+	DisallowServerCalls
+
 	// client is the originating client.
 	client *Client
 
@@ -283,6 +285,39 @@ func (c *clientFile) Close() error {
 	return nil
 }
 
+// SetAttrClose implements File.SetAttrClose.
+func (c *clientFile) SetAttrClose(valid SetAttrMask, attr SetAttr) error {
+	if !versionSupportsTsetattrclunk(c.client.version) {
+		setAttrErr := c.SetAttr(valid, attr)
+
+		// Try to close file even in case of failure above. Since the state of the
+		// file is unknown to the caller, it will not attempt to close the file
+		// again.
+		if err := c.Close(); err != nil {
+			return err
+		}
+
+		return setAttrErr
+	}
+
+	// Avoid double close.
+	if !atomic.CompareAndSwapUint32(&c.closed, 0, 1) {
+		return syscall.EBADF
+	}
+
+	// Send the message.
+	if err := c.client.sendRecv(&Tsetattrclunk{FID: c.fid, Valid: valid, SetAttr: attr}, &Rsetattrclunk{}); err != nil {
+		// If an error occurred, we toss away the FID. This isn't ideal,
+		// but I'm not sure what else makes sense in this context.
+		log.Warningf("Tsetattrclunk failed, losing FID %v: %v", c.fid, err)
+		return err
+	}
+
+	// Return the FID to the pool.
+	c.client.fidPool.Put(uint64(c.fid))
+	return nil
+}
+
 // Open implements File.Open.
 func (c *clientFile) Open(flags OpenFlags) (*fd.FD, QID, uint32, error) {
 	if atomic.LoadUint32(&c.closed) != 0 {
@@ -681,6 +716,3 @@ func (c *clientFile) Flush() error {
 
 	return c.client.sendRecv(&Tflushf{FID: c.fid}, &Rflushf{})
 }
-
-// Renamed implements File.Renamed.
-func (c *clientFile) Renamed(newDir File, newName string) {}
diff --git a/pkg/p9/file.go b/pkg/p9/file.go
index cab35896f..c2e3a3f98 100644
--- a/pkg/p9/file.go
+++ b/pkg/p9/file.go
@@ -135,6 +135,14 @@ type File interface {
 	// On the server, Close has no concurrency guarantee.
 	Close() error
 
+	// SetAttrClose is the equivalent of calling SetAttr() followed by Close().
+	// This can be used to set file times before closing the file in a single
+	// operation.
+	//
+	// On the server, SetAttr has a write concurrency guarantee.
+	// On the server, Close has no concurrency guarantee.
+	SetAttrClose(valid SetAttrMask, attr SetAttr) error
+
 	// Open must be called prior to using Read, Write or Readdir. Once Open
 	// is called, some operations, such as Walk, will no longer work.
 	//
@@ -286,3 +294,19 @@ type DefaultWalkGetAttr struct{}
 func (DefaultWalkGetAttr) WalkGetAttr([]string) ([]QID, File, AttrMask, Attr, error) {
 	return nil, nil, AttrMask{}, Attr{}, syscall.ENOSYS
 }
+
+// DisallowClientCalls panics if a client-only function is called.
+type DisallowClientCalls struct{}
+
+// SetAttrClose implements File.SetAttrClose.
+func (DisallowClientCalls) SetAttrClose(SetAttrMask, SetAttr) error {
+	panic("SetAttrClose should not be called on the server")
+}
+
+// DisallowServerCalls panics if a server-only function is called.
+type DisallowServerCalls struct{}
+
+// Renamed implements File.Renamed.
+func (*clientFile) Renamed(File, string) {
+	panic("Renamed should not be called on the client")
+}
diff --git a/pkg/p9/handlers.go b/pkg/p9/handlers.go
index 1db5797dd..abd237f46 100644
--- a/pkg/p9/handlers.go
+++ b/pkg/p9/handlers.go
@@ -123,6 +123,37 @@ func (t *Tclunk) handle(cs *connState) message {
 	return &Rclunk{}
 }
 
+func (t *Tsetattrclunk) handle(cs *connState) message {
+	ref, ok := cs.LookupFID(t.FID)
+	if !ok {
+		return newErr(syscall.EBADF)
+	}
+	defer ref.DecRef()
+
+	setAttrErr := ref.safelyWrite(func() error {
+		// We don't allow setattr on files that have been deleted.
+		// This might be technically incorrect, as it's possible that
+		// there were multiple links and you can still change the
+		// corresponding inode information.
+		if ref.isDeleted() {
+			return syscall.EINVAL
+		}
+
+		// Set the attributes.
+		return ref.file.SetAttr(t.Valid, t.SetAttr)
+	})
+
+	// Try to delete FID even in case of failure above. Since the state of the
+	// file is unknown to the caller, it will not attempt to close the file again.
+	if !cs.DeleteFID(t.FID) {
+		return newErr(syscall.EBADF)
+	}
+	if setAttrErr != nil {
+		return newErr(setAttrErr)
+	}
+	return &Rsetattrclunk{}
+}
+
 // handle implements handler.handle.
 func (t *Tremove) handle(cs *connState) message {
 	ref, ok := cs.LookupFID(t.FID)
diff --git a/pkg/p9/messages.go b/pkg/p9/messages.go
index 2cb59f934..cf13cbb69 100644
--- a/pkg/p9/messages.go
+++ b/pkg/p9/messages.go
@@ -317,6 +317,64 @@ func (r *Rclunk) String() string {
 	return "Rclunk{}"
 }
 
+// Tsetattrclunk is a setattr+close request.
+type Tsetattrclunk struct {
+	// FID is the FID to change.
+	FID FID
+
+	// Valid is the set of bits which will be used.
+	Valid SetAttrMask
+
+	// SetAttr is the set request.
+	SetAttr SetAttr
+}
+
+// decode implements encoder.decode.
+func (t *Tsetattrclunk) decode(b *buffer) {
+	t.FID = b.ReadFID()
+	t.Valid.decode(b)
+	t.SetAttr.decode(b)
+}
+
+// encode implements encoder.encode.
+func (t *Tsetattrclunk) encode(b *buffer) {
+	b.WriteFID(t.FID)
+	t.Valid.encode(b)
+	t.SetAttr.encode(b)
+}
+
+// Type implements message.Type.
+func (*Tsetattrclunk) Type() MsgType {
+	return MsgTsetattrclunk
+}
+
+// String implements fmt.Stringer.
+func (t *Tsetattrclunk) String() string {
+	return fmt.Sprintf("Tsetattrclunk{FID: %d, Valid: %v, SetAttr: %s}", t.FID, t.Valid, t.SetAttr)
+}
+
+// Rsetattrclunk is a setattr+close response.
+type Rsetattrclunk struct {
+}
+
+// decode implements encoder.decode.
+func (*Rsetattrclunk) decode(*buffer) {
+}
+
+// encode implements encoder.encode.
+func (*Rsetattrclunk) encode(*buffer) {
+}
+
+// Type implements message.Type.
+func (*Rsetattrclunk) Type() MsgType {
+	return MsgRsetattrclunk
+}
+
+// String implements fmt.Stringer.
+func (r *Rsetattrclunk) String() string {
+	return "Rsetattrclunk{}"
+}
+
 // Tremove is a remove request.
 //
 // This will eventually be replaced by Tunlinkat.
@@ -2657,6 +2715,8 @@ func init() {
 	msgRegistry.register(MsgRlconnect, func() message { return &Rlconnect{} })
 	msgRegistry.register(MsgTallocate, func() message { return &Tallocate{} })
 	msgRegistry.register(MsgRallocate, func() message { return &Rallocate{} })
+	msgRegistry.register(MsgTsetattrclunk, func() message { return &Tsetattrclunk{} })
+	msgRegistry.register(MsgRsetattrclunk, func() message { return &Rsetattrclunk{} })
 	msgRegistry.register(MsgTchannel, func() message { return &Tchannel{} })
 	msgRegistry.register(MsgRchannel, func() message { return &Rchannel{} })
 }
diff --git a/pkg/p9/messages_test.go b/pkg/p9/messages_test.go
index 7facc9f5e..bfeb6c236 100644
--- a/pkg/p9/messages_test.go
+++ b/pkg/p9/messages_test.go
@@ -376,6 +376,30 @@ func TestEncodeDecode(t *testing.T) {
 		&Rumknod{
 			Rmknod{QID: QID{Type: 1}},
 		},
+		&Tsetattrclunk{
+			FID: 1,
+			Valid: SetAttrMask{
+				Permissions:        true,
+				UID:                true,
+				GID:                true,
+				Size:               true,
+				ATime:              true,
+				MTime:              true,
+				CTime:              true,
+				ATimeNotSystemTime: true,
+				MTimeNotSystemTime: true,
+			},
+			SetAttr: SetAttr{
+				Permissions:      1,
+				UID:              2,
+				GID:              3,
+				Size:             4,
+				ATimeSeconds:     5,
+				ATimeNanoSeconds: 6,
+				MTimeSeconds:     7,
+				MTimeNanoSeconds: 8,
+			},
+		},
 	}
 
 	for _, enc := range objs {
diff --git a/pkg/p9/p9.go b/pkg/p9/p9.go
index 122c457d2..2235f8968 100644
--- a/pkg/p9/p9.go
+++ b/pkg/p9/p9.go
@@ -315,86 +315,88 @@ type MsgType uint8
 
 // MsgType declarations.
 const (
-	MsgTlerror      MsgType = 6
-	MsgRlerror              = 7
-	MsgTstatfs              = 8
-	MsgRstatfs              = 9
-	MsgTlopen               = 12
-	MsgRlopen               = 13
-	MsgTlcreate             = 14
-	MsgRlcreate             = 15
-	MsgTsymlink             = 16
-	MsgRsymlink             = 17
-	MsgTmknod               = 18
-	MsgRmknod               = 19
-	MsgTrename              = 20
-	MsgRrename              = 21
-	MsgTreadlink            = 22
-	MsgRreadlink            = 23
-	MsgTgetattr             = 24
-	MsgRgetattr             = 25
-	MsgTsetattr             = 26
-	MsgRsetattr             = 27
-	MsgTlistxattr           = 28
-	MsgRlistxattr           = 29
-	MsgTxattrwalk           = 30
-	MsgRxattrwalk           = 31
-	MsgTxattrcreate         = 32
-	MsgRxattrcreate         = 33
-	MsgTgetxattr            = 34
-	MsgRgetxattr            = 35
-	MsgTsetxattr            = 36
-	MsgRsetxattr            = 37
-	MsgTremovexattr         = 38
-	MsgRremovexattr         = 39
-	MsgTreaddir             = 40
-	MsgRreaddir             = 41
-	MsgTfsync               = 50
-	MsgRfsync               = 51
-	MsgTlink                = 70
-	MsgRlink                = 71
-	MsgTmkdir               = 72
-	MsgRmkdir               = 73
-	MsgTrenameat            = 74
-	MsgRrenameat            = 75
-	MsgTunlinkat            = 76
-	MsgRunlinkat            = 77
-	MsgTversion             = 100
-	MsgRversion             = 101
-	MsgTauth                = 102
-	MsgRauth                = 103
-	MsgTattach              = 104
-	MsgRattach              = 105
-	MsgTflush               = 108
-	MsgRflush               = 109
-	MsgTwalk                = 110
-	MsgRwalk                = 111
-	MsgTread                = 116
-	MsgRread                = 117
-	MsgTwrite               = 118
-	MsgRwrite               = 119
-	MsgTclunk               = 120
-	MsgRclunk               = 121
-	MsgTremove              = 122
-	MsgRremove              = 123
-	MsgTflushf              = 124
-	MsgRflushf              = 125
-	MsgTwalkgetattr         = 126
-	MsgRwalkgetattr         = 127
-	MsgTucreate             = 128
-	MsgRucreate             = 129
-	MsgTumkdir              = 130
-	MsgRumkdir              = 131
-	MsgTumknod              = 132
-	MsgRumknod              = 133
-	MsgTusymlink            = 134
-	MsgRusymlink            = 135
-	MsgTlconnect            = 136
-	MsgRlconnect            = 137
-	MsgTallocate            = 138
-	MsgRallocate            = 139
-	MsgTchannel             = 250
-	MsgRchannel             = 251
+	MsgTlerror       MsgType = 6
+	MsgRlerror       MsgType = 7
+	MsgTstatfs       MsgType = 8
+	MsgRstatfs       MsgType = 9
+	MsgTlopen        MsgType = 12
+	MsgRlopen        MsgType = 13
+	MsgTlcreate      MsgType = 14
+	MsgRlcreate      MsgType = 15
+	MsgTsymlink      MsgType = 16
+	MsgRsymlink      MsgType = 17
+	MsgTmknod        MsgType = 18
+	MsgRmknod        MsgType = 19
+	MsgTrename       MsgType = 20
+	MsgRrename       MsgType = 21
+	MsgTreadlink     MsgType = 22
+	MsgRreadlink     MsgType = 23
+	MsgTgetattr      MsgType = 24
+	MsgRgetattr      MsgType = 25
+	MsgTsetattr      MsgType = 26
+	MsgRsetattr      MsgType = 27
+	MsgTlistxattr    MsgType = 28
+	MsgRlistxattr    MsgType = 29
+	MsgTxattrwalk    MsgType = 30
+	MsgRxattrwalk    MsgType = 31
+	MsgTxattrcreate  MsgType = 32
+	MsgRxattrcreate  MsgType = 33
+	MsgTgetxattr     MsgType = 34
+	MsgRgetxattr     MsgType = 35
+	MsgTsetxattr     MsgType = 36
+	MsgRsetxattr     MsgType = 37
+	MsgTremovexattr  MsgType = 38
+	MsgRremovexattr  MsgType = 39
+	MsgTreaddir      MsgType = 40
+	MsgRreaddir      MsgType = 41
+	MsgTfsync        MsgType = 50
+	MsgRfsync        MsgType = 51
+	MsgTlink         MsgType = 70
+	MsgRlink         MsgType = 71
+	MsgTmkdir        MsgType = 72
+	MsgRmkdir        MsgType = 73
+	MsgTrenameat     MsgType = 74
+	MsgRrenameat     MsgType = 75
+	MsgTunlinkat     MsgType = 76
+	MsgRunlinkat     MsgType = 77
+	MsgTversion      MsgType = 100
+	MsgRversion      MsgType = 101
+	MsgTauth         MsgType = 102
+	MsgRauth         MsgType = 103
+	MsgTattach       MsgType = 104
+	MsgRattach       MsgType = 105
+	MsgTflush        MsgType = 108
+	MsgRflush        MsgType = 109
+	MsgTwalk         MsgType = 110
+	MsgRwalk         MsgType = 111
+	MsgTread         MsgType = 116
+	MsgRread         MsgType = 117
+	MsgTwrite        MsgType = 118
+	MsgRwrite        MsgType = 119
+	MsgTclunk        MsgType = 120
+	MsgRclunk        MsgType = 121
+	MsgTremove       MsgType = 122
+	MsgRremove       MsgType = 123
+	MsgTflushf       MsgType = 124
+	MsgRflushf       MsgType = 125
+	MsgTwalkgetattr  MsgType = 126
+	MsgRwalkgetattr  MsgType = 127
+	MsgTucreate      MsgType = 128
+	MsgRucreate      MsgType = 129
+	MsgTumkdir       MsgType = 130
+	MsgRumkdir       MsgType = 131
+	MsgTumknod       MsgType = 132
+	MsgRumknod       MsgType = 133
+	MsgTusymlink     MsgType = 134
+	MsgRusymlink     MsgType = 135
+	MsgTlconnect     MsgType = 136
+	MsgRlconnect     MsgType = 137
+	MsgTallocate     MsgType = 138
+	MsgRallocate     MsgType = 139
+	MsgTsetattrclunk MsgType = 140
+	MsgRsetattrclunk MsgType = 141
+	MsgTchannel      MsgType = 250
+	MsgRchannel      MsgType = 251
 )
 
 // QIDType represents the file type for QIDs.
diff --git a/pkg/p9/p9test/client_test.go b/pkg/p9/p9test/client_test.go
index 6e7bb3db2..6e605b14c 100644
--- a/pkg/p9/p9test/client_test.go
+++ b/pkg/p9/p9test/client_test.go
@@ -1225,22 +1225,31 @@ func TestOpen(t *testing.T) {
 func TestClose(t *testing.T) {
 	type closeTest struct {
 		name    string
-		closeFn func(backend *Mock, f p9.File)
+		closeFn func(backend *Mock, f p9.File) error
 	}
 
 	cases := []closeTest{
 		{
 			name: "close",
-			closeFn: func(_ *Mock, f p9.File) {
-				f.Close()
+			closeFn: func(_ *Mock, f p9.File) error {
+				return f.Close()
 			},
 		},
 		{
 			name: "remove",
-			closeFn: func(backend *Mock, f p9.File) {
+			closeFn: func(backend *Mock, f p9.File) error {
 				// Allow the rename call in the parent, automatically translated.
 				backend.parent.EXPECT().UnlinkAt(gomock.Any(), gomock.Any()).Times(1)
-				f.(deprecatedRemover).Remove()
+				return f.(deprecatedRemover).Remove()
+			},
+		},
+		{
+			name: "setAttrClose",
+			closeFn: func(backend *Mock, f p9.File) error {
+				valid := p9.SetAttrMask{ATime: true}
+				attr := p9.SetAttr{ATimeSeconds: 1, ATimeNanoSeconds: 2}
+				backend.EXPECT().SetAttr(valid, attr).Times(1)
+				return f.SetAttrClose(valid, attr)
 			},
 		},
 	}
@@ -1258,7 +1267,9 @@ func TestClose(t *testing.T) {
 				_, backend, f := walkHelper(h, name, root)
 
 				// Close via the prescribed method.
-				tc.closeFn(backend, f)
+				if err := tc.closeFn(backend, f); err != nil {
+					t.Fatalf("closeFn failed: %v", err)
+				}
 
 				// Everything should fail with EBADF.
 				if _, _, err := f.Walk(nil); err != syscall.EBADF {
diff --git a/pkg/p9/version.go b/pkg/p9/version.go
index 09cde9f5a..8d7168ef5 100644
--- a/pkg/p9/version.go
+++ b/pkg/p9/version.go
@@ -26,7 +26,7 @@ const (
 	//
 	// Clients are expected to start requesting this version number and
 	// to continuously decrement it until a Tversion request succeeds.
-	highestSupportedVersion uint32 = 11
+	highestSupportedVersion uint32 = 12
 
 	// lowestSupportedVersion is the lowest supported version X in a
 	// version string of the format 9P2000.L.Google.X.
@@ -173,3 +173,9 @@ func versionSupportsGetSetXattr(v uint32) bool {
 func versionSupportsListRemoveXattr(v uint32) bool {
 	return v >= 11
 }
+
+// versionSupportsTsetattrclunk returns true if version v supports
+// the Tsetattrclunk message.
+func versionSupportsTsetattrclunk(v uint32) bool {
+	return v >= 12
+}