sentry: Adds canonical mode support.

PiperOrigin-RevId: 196331627
Change-Id: Ifef4485f8202c52481af317cedd52d2ef48cea6a

pkg/abi/linux/tty.go

@@ -14,9 +14,16 @@
 
 package linux
 
+import (
+	"unicode/utf8"
+)
+
 const (
 	// NumControlCharacters is the number of control characters in Termios.
 	NumControlCharacters = 19
+	// disabledChar is used to indicate that a control character is
+	// disabled.
+	disabledChar = 0
 )
 
 // Termios is struct termios, defined in uapi/asm-generic/termbits.h.
@@ -86,6 +93,27 @@ func (t *KernelTermios) FromTermios(term Termios) {
 	t.ControlCharacters = term.ControlCharacters
 }
 
+// IsTerminating returns whether c is a line terminating character.
+func (t *KernelTermios) IsTerminating(c rune) bool {
+	if t.IsEOF(c) {
+		return true
+	}
+	switch byte(c) {
+	case disabledChar:
+		return false
+	case '\n', t.ControlCharacters[VEOL]:
+		return true
+	case t.ControlCharacters[VEOL2]:
+		return t.LEnabled(IEXTEN)
+	}
+	return false
+}
+
+// IsEOF returns whether c is the EOF character.
+func (t *KernelTermios) IsEOF(c rune) bool {
+	return utf8.RuneLen(c) == 1 && byte(c) == t.ControlCharacters[VEOF] && t.ControlCharacters[VEOF] != disabledChar
+}
+
 // Input flags.
 const (
 	IGNBRK  = 0000001

pkg/sentry/fs/tty/master.go

@@ -148,6 +148,9 @@ func (mf *masterFileOperations) Write(ctx context.Context, _ *fs.File, src userm
 // Ioctl implements fs.FileOperations.Ioctl.
 func (mf *masterFileOperations) Ioctl(ctx context.Context, io usermem.IO, args arch.SyscallArguments) (uintptr, error) {
 	switch args[1].Uint() {
+	case linux.FIONREAD: // linux.FIONREAD == linux.TIOCINQ
+		// Get the number of bytes in the output queue read buffer.
+		return 0, mf.t.ld.outputQueueReadSize(ctx, io, args)
 	case linux.TCGETS:
 		// N.B. TCGETS on the master actually returns the configuration
 		// of the slave end.

pkg/sentry/fs/tty/slave.go

@@ -133,6 +133,9 @@ func (sf *slaveFileOperations) Write(ctx context.Context, _ *fs.File, src userme
 // Ioctl implements fs.FileOperations.Ioctl.
 func (sf *slaveFileOperations) Ioctl(ctx context.Context, io usermem.IO, args arch.SyscallArguments) (uintptr, error) {
 	switch args[1].Uint() {
+	case linux.FIONREAD: // linux.FIONREAD == linux.TIOCINQ
+		// Get the number of bytes in the input queue read buffer.
+		return 0, sf.si.t.ld.inputQueueReadSize(ctx, io, args)
 	case linux.TCGETS:
 		return sf.si.t.ld.getTermios(ctx, io, args)
 	case linux.TCSETS: