Plumb getting/setting xattrs through InodeOperations and 9p gofer interfaces.

There was a very bare get/setxattr in the InodeOperations interface. Add
context.Context to both, size to getxattr, and flags to setxattr.
Note that extended attributes are passed around as strings in this
implementation, so size is automatically encoded into the value. Size is
added in getxattr so that implementations can return ERANGE if a value is larger
than can fit in the user-allocated buffer. This prevents us from unnecessarily
passing around an arbitrarily large xattr when the user buffer is actually too
small.

Don't use the existing xattrwalk and xattrcreate messages and define our
own, mainly for the sake of simplicity.

Extended attributes will be implemented in future commits.

PiperOrigin-RevId: 290121300

6 files changed, 216 insertions, 0 deletions

diff --git a/pkg/p9/client_file.go b/pkg/p9/client_file.go
index de9357389..04b584383 100644
--- a/pkg/p9/client_file.go
+++ b/pkg/p9/client_file.go
@@ -165,6 +165,29 @@ func (c *clientFile) SetAttr(valid SetAttrMask, attr SetAttr) error {
 	return c.client.sendRecv(&Tsetattr{FID: c.fid, Valid: valid, SetAttr: attr}, &Rsetattr{})
 }
 
+// GetXattr implements File.GetXattr.
+func (c *clientFile) GetXattr(name string, size uint64) (string, error) {
+	if atomic.LoadUint32(&c.closed) != 0 {
+		return "", syscall.EBADF
+	}
+
+	rgetxattr := Rgetxattr{}
+	if err := c.client.sendRecv(&Tgetxattr{FID: c.fid, Name: name, Size: size}, &rgetxattr); err != nil {
+		return "", err
+	}
+
+	return rgetxattr.Value, nil
+}
+
+// SetXattr implements File.SetXattr.
+func (c *clientFile) SetXattr(name, value string, flags uint32) error {
+	if atomic.LoadUint32(&c.closed) != 0 {
+		return syscall.EBADF
+	}
+
+	return c.client.sendRecv(&Tsetxattr{FID: c.fid, Name: name, Value: value, Flags: flags}, &Rsetxattr{})
+}
+
 // Allocate implements File.Allocate.
 func (c *clientFile) Allocate(mode AllocateMode, offset, length uint64) error {
 	if atomic.LoadUint32(&c.closed) != 0 {
diff --git a/pkg/p9/file.go b/pkg/p9/file.go
index 96d1f2a8e..4607cfcdf 100644
--- a/pkg/p9/file.go
+++ b/pkg/p9/file.go
@@ -89,6 +89,22 @@ type File interface {
 	// On the server, SetAttr has a write concurrency guarantee.
 	SetAttr(valid SetAttrMask, attr SetAttr) error
 
+	// GetXattr returns extended attributes of this node.
+	//
+	// Size indicates the size of the buffer that has been allocated to hold the
+	// attribute value. If the value is larger than size, implementations may
+	// return ERANGE to indicate that the buffer is too small, but they are also
+	// free to ignore the hint entirely (i.e. the value returned may be larger
+	// than size). All size checking is done independently at the syscall layer.
+	//
+	// TODO(b/127675828): Determine concurrency guarantees once implemented.
+	GetXattr(name string, size uint64) (string, error)
+
+	// SetXattr sets extended attributes on this node.
+	//
+	// TODO(b/127675828): Determine concurrency guarantees once implemented.
+	SetXattr(name, value string, flags uint32) error
+
 	// Allocate allows the caller to directly manipulate the allocated disk space
 	// for the file. See fallocate(2) for more details.
 	Allocate(mode AllocateMode, offset, length uint64) error
diff --git a/pkg/p9/handlers.go b/pkg/p9/handlers.go
index b9582c07f..7d6653a07 100644
--- a/pkg/p9/handlers.go
+++ b/pkg/p9/handlers.go
@@ -913,6 +913,35 @@ func (t *Txattrcreate) handle(cs *connState) message {
 }
 
 // handle implements handler.handle.
+func (t *Tgetxattr) handle(cs *connState) message {
+	ref, ok := cs.LookupFID(t.FID)
+	if !ok {
+		return newErr(syscall.EBADF)
+	}
+	defer ref.DecRef()
+
+	val, err := ref.file.GetXattr(t.Name, t.Size)
+	if err != nil {
+		return newErr(err)
+	}
+	return &Rgetxattr{Value: val}
+}
+
+// handle implements handler.handle.
+func (t *Tsetxattr) handle(cs *connState) message {
+	ref, ok := cs.LookupFID(t.FID)
+	if !ok {
+		return newErr(syscall.EBADF)
+	}
+	defer ref.DecRef()
+
+	if err := ref.file.SetXattr(t.Name, t.Value, t.Flags); err != nil {
+		return newErr(err)
+	}
+	return &Rsetxattr{}
+}
+
+// handle implements handler.handle.
 func (t *Treaddir) handle(cs *connState) message {
 	ref, ok := cs.LookupFID(t.Directory)
 	if !ok {
diff --git a/pkg/p9/messages.go b/pkg/p9/messages.go
index ffdd7e8c6..ceb723d86 100644
--- a/pkg/p9/messages.go
+++ b/pkg/p9/messages.go
@@ -1611,6 +1611,131 @@ func (r *Rxattrcreate) String() string {
 	return fmt.Sprintf("Rxattrcreate{}")
 }
 
+// Tgetxattr is a getxattr request.
+type Tgetxattr struct {
+	// FID refers to the file for which to get xattrs.
+	FID FID
+
+	// Name is the xattr to get.
+	Name string
+
+	// Size is the buffer size for the xattr to get.
+	Size uint64
+}
+
+// Decode implements encoder.Decode.
+func (t *Tgetxattr) Decode(b *buffer) {
+	t.FID = b.ReadFID()
+	t.Name = b.ReadString()
+	t.Size = b.Read64()
+}
+
+// Encode implements encoder.Encode.
+func (t *Tgetxattr) Encode(b *buffer) {
+	b.WriteFID(t.FID)
+	b.WriteString(t.Name)
+	b.Write64(t.Size)
+}
+
+// Type implements message.Type.
+func (*Tgetxattr) Type() MsgType {
+	return MsgTgetxattr
+}
+
+// String implements fmt.Stringer.
+func (t *Tgetxattr) String() string {
+	return fmt.Sprintf("Tgetxattr{FID: %d, Name: %s, Size: %d}", t.FID, t.Name, t.Size)
+}
+
+// Rgetxattr is a getxattr response.
+type Rgetxattr struct {
+	// Value is the extended attribute value.
+	Value string
+}
+
+// Decode implements encoder.Decode.
+func (r *Rgetxattr) Decode(b *buffer) {
+	r.Value = b.ReadString()
+}
+
+// Encode implements encoder.Encode.
+func (r *Rgetxattr) Encode(b *buffer) {
+	b.WriteString(r.Value)
+}
+
+// Type implements message.Type.
+func (*Rgetxattr) Type() MsgType {
+	return MsgRgetxattr
+}
+
+// String implements fmt.Stringer.
+func (r *Rgetxattr) String() string {
+	return fmt.Sprintf("Rgetxattr{Value: %s}", r.Value)
+}
+
+// Tsetxattr sets extended attributes.
+type Tsetxattr struct {
+	// FID refers to the file on which to set xattrs.
+	FID FID
+
+	// Name is the attribute name.
+	Name string
+
+	// Value is the attribute value.
+	Value string
+
+	// Linux setxattr(2) flags.
+	Flags uint32
+}
+
+// Decode implements encoder.Decode.
+func (t *Tsetxattr) Decode(b *buffer) {
+	t.FID = b.ReadFID()
+	t.Name = b.ReadString()
+	t.Value = b.ReadString()
+	t.Flags = b.Read32()
+}
+
+// Encode implements encoder.Encode.
+func (t *Tsetxattr) Encode(b *buffer) {
+	b.WriteFID(t.FID)
+	b.WriteString(t.Name)
+	b.WriteString(t.Value)
+	b.Write32(t.Flags)
+}
+
+// Type implements message.Type.
+func (*Tsetxattr) Type() MsgType {
+	return MsgTsetxattr
+}
+
+// String implements fmt.Stringer.
+func (t *Tsetxattr) String() string {
+	return fmt.Sprintf("Tsetxattr{FID: %d, Name: %s, Value: %s, Flags: %d}", t.FID, t.Name, t.Value, t.Flags)
+}
+
+// Rsetxattr is a setxattr response.
+type Rsetxattr struct {
+}
+
+// Decode implements encoder.Decode.
+func (r *Rsetxattr) Decode(b *buffer) {
+}
+
+// Encode implements encoder.Encode.
+func (r *Rsetxattr) Encode(b *buffer) {
+}
+
+// Type implements message.Type.
+func (*Rsetxattr) Type() MsgType {
+	return MsgRsetxattr
+}
+
+// String implements fmt.Stringer.
+func (r *Rsetxattr) String() string {
+	return fmt.Sprintf("Rsetxattr{}")
+}
+
 // Treaddir is a readdir request.
 type Treaddir struct {
 	// Directory is the directory FID to read.
@@ -2363,6 +2488,10 @@ func init() {
 	msgRegistry.register(MsgRxattrwalk, func() message { return &Rxattrwalk{} })
 	msgRegistry.register(MsgTxattrcreate, func() message { return &Txattrcreate{} })
 	msgRegistry.register(MsgRxattrcreate, func() message { return &Rxattrcreate{} })
+	msgRegistry.register(MsgTgetxattr, func() message { return &Tgetxattr{} })
+	msgRegistry.register(MsgRgetxattr, func() message { return &Rgetxattr{} })
+	msgRegistry.register(MsgTsetxattr, func() message { return &Tsetxattr{} })
+	msgRegistry.register(MsgRsetxattr, func() message { return &Rsetxattr{} })
 	msgRegistry.register(MsgTreaddir, func() message { return &Treaddir{} })
 	msgRegistry.register(MsgRreaddir, func() message { return &Rreaddir{} })
 	msgRegistry.register(MsgTfsync, func() message { return &Tfsync{} })
diff --git a/pkg/p9/messages_test.go b/pkg/p9/messages_test.go
index 6ba6a1654..825c939da 100644
--- a/pkg/p9/messages_test.go
+++ b/pkg/p9/messages_test.go
@@ -194,6 +194,21 @@ func TestEncodeDecode(t *testing.T) {
 			Flags:    3,
 		},
 		&Rxattrcreate{},
+		&Tgetxattr{
+			FID:  1,
+			Name: "abc",
+			Size: 2,
+		},
+		&Rgetxattr{
+			Value: "xyz",
+		},
+		&Tsetxattr{
+			FID:   1,
+			Name:  "abc",
+			Value: "xyz",
+			Flags: 2,
+		},
+		&Rsetxattr{},
 		&Treaddir{
 			Directory: 1,
 			Offset:    2,
diff --git a/pkg/p9/p9.go b/pkg/p9/p9.go
index d3090535a..5ab00d625 100644
--- a/pkg/p9/p9.go
+++ b/pkg/p9/p9.go
@@ -339,6 +339,10 @@ const (
 	MsgRxattrwalk           = 31
 	MsgTxattrcreate         = 32
 	MsgRxattrcreate         = 33
+	MsgTgetxattr            = 34
+	MsgRgetxattr            = 35
+	MsgTsetxattr            = 36
+	MsgRsetxattr            = 37
 	MsgTreaddir             = 40
 	MsgRreaddir             = 41
 	MsgTfsync               = 50