Sentry: split tty.queue into its own file.

Minor refactor. line_discipline.go was home to 2 large structs (lineDiscipline
and queue), and queue is now large enough IMO to get its own file.

Also moves queue locks into the queue struct, making locking simpler.

PiperOrigin-RevId: 200080301
Change-Id: Ia75a0e9b3d9ac8d7e5a0f0099a54e1f5b8bdea34

1 files changed, 218 insertions, 0 deletions

diff --git a/pkg/sentry/fs/tty/queue.go b/pkg/sentry/fs/tty/queue.go
new file mode 100644
index 000000000..026d5e077
--- /dev/null
+++ b/pkg/sentry/fs/tty/queue.go
@@ -0,0 +1,218 @@
+// Copyright 2018 Google 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 tty
+
+import (
+	"bytes"
+	"sync"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+)
+
+// queue represents one of the input or output queues between a pty master and
+// slave. Bytes written to a queue are added to the read buffer until it is
+// full, at which point they are written to the wait buffer. Bytes are
+// processed (i.e. undergo termios transformations) as they are added to the
+// read buffer. The read buffer is readable when its length is nonzero and
+// readable is true.
+type queue struct {
+	// mu protects everything in queue.
+	mu sync.Mutex `state:"nosave"`
+
+	waiter.Queue `state:"nosave"`
+
+	// readBuf is buffer of data ready to be read when readable is true.
+	// This data has been processed.
+	readBuf bytes.Buffer `state:".([]byte)"`
+
+	// waitBuf contains data that can't fit into readBuf. It is put here
+	// until it can be loaded into the read buffer. waitBuf contains data
+	// that hasn't been processed.
+	waitBuf bytes.Buffer `state:".([]byte)"`
+
+	// readable indicates whether the read buffer can be read from.  In
+	// canonical mode, there can be an unterminated line in the read buffer,
+	// so readable must be checked.
+	readable bool
+
+	// transform is the the queue's function for transforming bytes
+	// entering the queue. For example, transform might convert all '\r's
+	// entering the queue to '\n's.
+	transformer
+}
+
+// saveReadBuf is invoked by stateify.
+func (q *queue) saveReadBuf() []byte {
+	return append([]byte(nil), q.readBuf.Bytes()...)
+}
+
+// loadReadBuf is invoked by stateify.
+func (q *queue) loadReadBuf(b []byte) {
+	q.readBuf.Write(b)
+}
+
+// saveWaitBuf is invoked by stateify.
+func (q *queue) saveWaitBuf() []byte {
+	return append([]byte(nil), q.waitBuf.Bytes()...)
+}
+
+// loadWaitBuf is invoked by stateify.
+func (q *queue) loadWaitBuf(b []byte) {
+	q.waitBuf.Write(b)
+}
+
+// readReadiness returns whether q is ready to be read from.
+func (q *queue) readReadiness(t *linux.KernelTermios) waiter.EventMask {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	if q.readBuf.Len() > 0 && q.readable {
+		return waiter.EventIn
+	}
+	return waiter.EventMask(0)
+}
+
+// writeReadiness returns whether q is ready to be written to.
+func (q *queue) writeReadiness(t *linux.KernelTermios) waiter.EventMask {
+	// Like Linux, we don't impose a maximum size on what can be enqueued.
+	return waiter.EventOut
+}
+
+// readableSize writes the number of readable bytes to userspace.
+func (q *queue) readableSize(ctx context.Context, io usermem.IO, args arch.SyscallArguments) error {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	var size int32
+	if q.readable {
+		size = int32(q.readBuf.Len())
+	}
+
+	_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), size, usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	return err
+
+}
+
+// read reads from q to userspace.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) read(ctx context.Context, dst usermem.IOSequence, l *lineDiscipline) (int64, error) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	if !q.readable {
+		return 0, syserror.ErrWouldBlock
+	}
+
+	// Read out from the read buffer.
+	n := canonMaxBytes
+	if n > int(dst.NumBytes()) {
+		n = int(dst.NumBytes())
+	}
+	if n > q.readBuf.Len() {
+		n = q.readBuf.Len()
+	}
+	n, err := dst.Writer(ctx).Write(q.readBuf.Bytes()[:n])
+	if err != nil {
+		return 0, err
+	}
+	// Discard bytes read out.
+	q.readBuf.Next(n)
+
+	// If we read everything, this queue is no longer readable.
+	if q.readBuf.Len() == 0 {
+		q.readable = false
+	}
+
+	// Move data from the queue's wait buffer to its read buffer.
+	q.pushWaitBufLocked(l)
+
+	// If state changed, notify any waiters. If nothing was available to
+	// read, let the caller know we could block.
+	if n > 0 {
+		q.Notify(waiter.EventOut)
+	} else {
+		return 0, syserror.ErrWouldBlock
+	}
+	return int64(n), nil
+}
+
+// write writes to q from userspace.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) write(ctx context.Context, src usermem.IOSequence, l *lineDiscipline) (int64, error) {
+	// TODO: Use CopyInTo/safemem to avoid extra copying.
+	// Copy in the bytes to write from user-space.
+	b := make([]byte, src.NumBytes())
+	n, err := src.CopyIn(ctx, b)
+	if err != nil {
+		return 0, err
+	}
+	b = b[:n]
+	return q.writeBytes(b, l)
+}
+
+// writeBytes writes to q from b.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) writeBytes(b []byte, l *lineDiscipline) (int64, error) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	// Write as much as possible to the read buffer.
+	n := q.transform(l, q, b)
+
+	// Write remaining data to the wait buffer.
+	nWaiting, _ := q.waitBuf.Write(b[n:])
+
+	// If state changed, notify any waiters. If we were unable to write
+	// anything, let the caller know we could block.
+	if n > 0 {
+		q.Notify(waiter.EventIn)
+	} else if nWaiting == 0 {
+		return 0, syserror.ErrWouldBlock
+	}
+	return int64(n + nWaiting), nil
+}
+
+// pushWaitBuf fills the queue's read buffer with data from the wait buffer.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) pushWaitBuf(l *lineDiscipline) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	q.pushWaitBufLocked(l)
+}
+
+// Preconditions:
+// * l.termiosMu must be held for reading.
+// * q.mu must be locked.
+func (q *queue) pushWaitBufLocked(l *lineDiscipline) {
+	// Remove bytes from the wait buffer and move them to the read buffer.
+	n := q.transform(l, q, q.waitBuf.Bytes())
+	q.waitBuf.Next(n)
+
+	// If state changed, notify any waiters.
+	if n > 0 {
+		q.Notify(waiter.EventIn)
+	}
+}