Implement fallocate(2)

Closes #225

PiperOrigin-RevId: 247508791
Change-Id: I04f47cf2770b30043e5a272aba4ba6e11d0476cc

8 files changed, 202 insertions, 1 deletions

diff --git a/pkg/p9/BUILD b/pkg/p9/BUILD
index 5d972309d..36b2ec5f6 100644
--- a/pkg/p9/BUILD
+++ b/pkg/p9/BUILD
@@ -26,6 +26,7 @@ go_library(
         "//pkg/fd",
         "//pkg/log",
         "//pkg/unet",
+        "@org_golang_x_sys//unix:go_default_library",
     ],
 )
 
diff --git a/pkg/p9/client_file.go b/pkg/p9/client_file.go
index 63c65129a..471c3a80b 100644
--- a/pkg/p9/client_file.go
+++ b/pkg/p9/client_file.go
@@ -171,6 +171,18 @@ func (c *clientFile) SetAttr(valid SetAttrMask, attr SetAttr) error {
 	return c.client.sendRecv(&Tsetattr{FID: c.fid, Valid: valid, SetAttr: attr}, &Rsetattr{})
 }
 
+// Allocate implements File.Allocate.
+func (c *clientFile) Allocate(mode AllocateMode, offset, length uint64) error {
+	if atomic.LoadUint32(&c.closed) != 0 {
+		return syscall.EBADF
+	}
+	if !versionSupportsTallocate(c.client.version) {
+		return syscall.EOPNOTSUPP
+	}
+
+	return c.client.sendRecv(&Tallocate{FID: c.fid, Mode: mode, Offset: offset, Length: length}, &Rallocate{})
+}
+
 // Remove implements File.Remove.
 //
 // N.B. This method is no longer part of the file interface and should be
diff --git a/pkg/p9/file.go b/pkg/p9/file.go
index a52a0f3e7..89e814d50 100644
--- a/pkg/p9/file.go
+++ b/pkg/p9/file.go
@@ -89,6 +89,10 @@ type File interface {
 	// On the server, SetAttr has a write concurrency guarantee.
 	SetAttr(valid SetAttrMask, attr SetAttr) 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
+
 	// Close is called when all references are dropped on the server side,
 	// and Close should be called by the client to drop all references.
 	//
diff --git a/pkg/p9/handlers.go b/pkg/p9/handlers.go
index 6da2ce4e3..533ead98a 100644
--- a/pkg/p9/handlers.go
+++ b/pkg/p9/handlers.go
@@ -878,6 +878,40 @@ func (t *Tsetattr) handle(cs *connState) message {
 }
 
 // handle implements handler.handle.
+func (t *Tallocate) handle(cs *connState) message {
+	// Lookup the FID.
+	ref, ok := cs.LookupFID(t.FID)
+	if !ok {
+		return newErr(syscall.EBADF)
+	}
+	defer ref.DecRef()
+
+	if err := ref.safelyWrite(func() error {
+		// Has it been opened already?
+		openFlags, opened := ref.OpenFlags()
+		if !opened {
+			return syscall.EINVAL
+		}
+
+		// Can it be written? Check permissions.
+		if openFlags&OpenFlagsModeMask == ReadOnly {
+			return syscall.EBADF
+		}
+
+		// We don't allow allocate on files that have been deleted.
+		if ref.isDeleted() {
+			return syscall.EINVAL
+		}
+
+		return ref.file.Allocate(t.Mode, t.Offset, t.Length)
+	}); err != nil {
+		return newErr(err)
+	}
+
+	return &Rallocate{}
+}
+
+// handle implements handler.handle.
 func (t *Txattrwalk) handle(cs *connState) message {
 	// Lookup the FID.
 	ref, ok := cs.LookupFID(t.FID)
diff --git a/pkg/p9/local_server/local_server.go b/pkg/p9/local_server/local_server.go
index f4077a9d4..d49d94550 100644
--- a/pkg/p9/local_server/local_server.go
+++ b/pkg/p9/local_server/local_server.go
@@ -323,6 +323,11 @@ func (l *local) Renamed(parent p9.File, newName string) {
 	l.path = path.Join(parent.(*local).path, newName)
 }
 
+// Allocate implements p9.File.Allocate.
+func (l *local) Allocate(mode p9.AllocateMode, offset, length uint64) error {
+	return syscall.Fallocate(int(l.file.Fd()), mode.ToLinux(), int64(offset), int64(length))
+}
+
 func main() {
 	log.SetLevel(log.Debug)
 
diff --git a/pkg/p9/messages.go b/pkg/p9/messages.go
index 3c7898cc1..703753c31 100644
--- a/pkg/p9/messages.go
+++ b/pkg/p9/messages.go
@@ -1424,6 +1424,63 @@ func (r *Rsetattr) String() string {
 	return fmt.Sprintf("Rsetattr{}")
 }
 
+// Tallocate is an allocate request. This is an extension to 9P protocol, not
+// present in the 9P2000.L standard.
+type Tallocate struct {
+	FID    FID
+	Mode   AllocateMode
+	Offset uint64
+	Length uint64
+}
+
+// Decode implements encoder.Decode.
+func (t *Tallocate) Decode(b *buffer) {
+	t.FID = b.ReadFID()
+	t.Mode.Decode(b)
+	t.Offset = b.Read64()
+	t.Length = b.Read64()
+}
+
+// Encode implements encoder.Encode.
+func (t *Tallocate) Encode(b *buffer) {
+	b.WriteFID(t.FID)
+	t.Mode.Encode(b)
+	b.Write64(t.Offset)
+	b.Write64(t.Length)
+}
+
+// Type implements message.Type.
+func (*Tallocate) Type() MsgType {
+	return MsgTallocate
+}
+
+// String implements fmt.Stringer.
+func (t *Tallocate) String() string {
+	return fmt.Sprintf("Tallocate{FID: %d, Offset: %d, Length: %d}", t.FID, t.Offset, t.Length)
+}
+
+// Rallocate is an allocate response.
+type Rallocate struct {
+}
+
+// Decode implements encoder.Decode.
+func (*Rallocate) Decode(b *buffer) {
+}
+
+// Encode implements encoder.Encode.
+func (*Rallocate) Encode(b *buffer) {
+}
+
+// Type implements message.Type.
+func (*Rallocate) Type() MsgType {
+	return MsgRallocate
+}
+
+// String implements fmt.Stringer.
+func (r *Rallocate) String() string {
+	return fmt.Sprintf("Rallocate{}")
+}
+
 // Txattrwalk walks extended attributes.
 type Txattrwalk struct {
 	// FID is the FID to check for attributes.
@@ -2297,4 +2354,6 @@ func init() {
 	msgRegistry.register(MsgRusymlink, func() message { return &Rusymlink{} })
 	msgRegistry.register(MsgTlconnect, func() message { return &Tlconnect{} })
 	msgRegistry.register(MsgRlconnect, func() message { return &Rlconnect{} })
+	msgRegistry.register(MsgTallocate, func() message { return &Tallocate{} })
+	msgRegistry.register(MsgRallocate, func() message { return &Rallocate{} })
 }
diff --git a/pkg/p9/p9.go b/pkg/p9/p9.go
index 78c7d3f86..4039862e6 100644
--- a/pkg/p9/p9.go
+++ b/pkg/p9/p9.go
@@ -22,6 +22,8 @@ import (
 	"strings"
 	"sync/atomic"
 	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 // OpenFlags is the mode passed to Open and Create operations.
@@ -374,6 +376,8 @@ const (
 	MsgRusymlink            = 135
 	MsgTlconnect            = 136
 	MsgRlconnect            = 137
+	MsgTallocate            = 138
+	MsgRallocate            = 139
 )
 
 // QIDType represents the file type for QIDs.
@@ -1058,3 +1062,80 @@ func (d *Dirent) Encode(b *buffer) {
 	b.WriteQIDType(d.Type)
 	b.WriteString(d.Name)
 }
+
+// AllocateMode are possible modes to p9.File.Allocate().
+type AllocateMode struct {
+	KeepSize      bool
+	PunchHole     bool
+	NoHideStale   bool
+	CollapseRange bool
+	ZeroRange     bool
+	InsertRange   bool
+	Unshare       bool
+}
+
+// ToLinux converts to a value compatible with fallocate(2)'s mode.
+func (a *AllocateMode) ToLinux() uint32 {
+	rv := uint32(0)
+	if a.KeepSize {
+		rv |= unix.FALLOC_FL_KEEP_SIZE
+	}
+	if a.PunchHole {
+		rv |= unix.FALLOC_FL_PUNCH_HOLE
+	}
+	if a.NoHideStale {
+		rv |= unix.FALLOC_FL_NO_HIDE_STALE
+	}
+	if a.CollapseRange {
+		rv |= unix.FALLOC_FL_COLLAPSE_RANGE
+	}
+	if a.ZeroRange {
+		rv |= unix.FALLOC_FL_ZERO_RANGE
+	}
+	if a.InsertRange {
+		rv |= unix.FALLOC_FL_INSERT_RANGE
+	}
+	if a.Unshare {
+		rv |= unix.FALLOC_FL_UNSHARE_RANGE
+	}
+	return rv
+}
+
+// Decode implements encoder.Decode.
+func (a *AllocateMode) Decode(b *buffer) {
+	mask := b.Read32()
+	a.KeepSize = mask&0x01 != 0
+	a.PunchHole = mask&0x02 != 0
+	a.NoHideStale = mask&0x04 != 0
+	a.CollapseRange = mask&0x08 != 0
+	a.ZeroRange = mask&0x10 != 0
+	a.InsertRange = mask&0x20 != 0
+	a.Unshare = mask&0x40 != 0
+}
+
+// Encode implements encoder.Encode.
+func (a *AllocateMode) Encode(b *buffer) {
+	mask := uint32(0)
+	if a.KeepSize {
+		mask |= 0x01
+	}
+	if a.PunchHole {
+		mask |= 0x02
+	}
+	if a.NoHideStale {
+		mask |= 0x04
+	}
+	if a.CollapseRange {
+		mask |= 0x08
+	}
+	if a.ZeroRange {
+		mask |= 0x10
+	}
+	if a.InsertRange {
+		mask |= 0x20
+	}
+	if a.Unshare {
+		mask |= 0x40
+	}
+	b.Write32(mask)
+}
diff --git a/pkg/p9/version.go b/pkg/p9/version.go
index a36a499a1..c2a2885ae 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 = 6
+	highestSupportedVersion uint32 = 7
 
 	// lowestSupportedVersion is the lowest supported version X in a
 	// version string of the format 9P2000.L.Google.X.
@@ -143,3 +143,8 @@ func VersionSupportsAnonymous(v uint32) bool {
 func VersionSupportsMultiUser(v uint32) bool {
 	return v >= 6
 }
+
+// versionSupportsTallocate returns true if version v supports Allocate().
+func versionSupportsTallocate(v uint32) bool {
+	return v >= 7
+}