Port devpts to VFS2.

PiperOrigin-RevId: 308164359

1 files changed, 240 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/devpts/queue.go b/pkg/sentry/fsimpl/devpts/queue.go
new file mode 100644
index 000000000..29a6be858
--- /dev/null
+++ b/pkg/sentry/fsimpl/devpts/queue.go
@@ -0,0 +1,240 @@
+// Copyright 2018 The gVisor Authors.
+//
+// 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 devpts
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// LINT.IfChange
+
+// waitBufMaxBytes is the maximum size of a wait buffer. It is based on
+// TTYB_DEFAULT_MEM_LIMIT.
+const waitBufMaxBytes = 131072
+
+// 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.
+//
+// +stateify savable
+type queue struct {
+	// mu protects everything in queue.
+	mu sync.Mutex `state:"nosave"`
+
+	// readBuf is buffer of data ready to be read when readable is true.
+	// This data has been processed.
+	readBuf []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    [][]byte
+	waitBufLen uint64
+
+	// 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
+}
+
+// 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 len(q.readBuf) > 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 {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	if q.waitBufLen < waitBufMaxBytes {
+		return waiter.EventOut
+	}
+	return waiter.EventMask(0)
+}
+
+// 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(len(q.readBuf))
+	}
+
+	_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), size, usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	return err
+
+}
+
+// read reads from q to userspace. It returns the number of bytes read as well
+// as whether the read caused more readable data to become available (whether
+// data was pushed from the wait buffer to the read buffer).
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) read(ctx context.Context, dst usermem.IOSequence, l *lineDiscipline) (int64, bool, error) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	if !q.readable {
+		return 0, false, syserror.ErrWouldBlock
+	}
+
+	if dst.NumBytes() > canonMaxBytes {
+		dst = dst.TakeFirst(canonMaxBytes)
+	}
+
+	n, err := dst.CopyOutFrom(ctx, safemem.ReaderFunc(func(dst safemem.BlockSeq) (uint64, error) {
+		src := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(q.readBuf))
+		n, err := safemem.CopySeq(dst, src)
+		if err != nil {
+			return 0, err
+		}
+		q.readBuf = q.readBuf[n:]
+
+		// If we read everything, this queue is no longer readable.
+		if len(q.readBuf) == 0 {
+			q.readable = false
+		}
+
+		return n, nil
+	}))
+	if err != nil {
+		return 0, false, err
+	}
+
+	// Move data from the queue's wait buffer to its read buffer.
+	nPushed := q.pushWaitBufLocked(l)
+
+	return int64(n), nPushed > 0, 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) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	// Copy data into the wait buffer.
+	n, err := src.CopyInTo(ctx, safemem.WriterFunc(func(src safemem.BlockSeq) (uint64, error) {
+		copyLen := src.NumBytes()
+		room := waitBufMaxBytes - q.waitBufLen
+		// If out of room, return EAGAIN.
+		if room == 0 && copyLen > 0 {
+			return 0, syserror.ErrWouldBlock
+		}
+		// Cap the size of the wait buffer.
+		if copyLen > room {
+			copyLen = room
+			src = src.TakeFirst64(room)
+		}
+		buf := make([]byte, copyLen)
+
+		// Copy the data into the wait buffer.
+		dst := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(buf))
+		n, err := safemem.CopySeq(dst, src)
+		if err != nil {
+			return 0, err
+		}
+		q.waitBufAppend(buf)
+
+		return n, nil
+	}))
+	if err != nil {
+		return 0, err
+	}
+
+	// Push data from the wait to the read buffer.
+	q.pushWaitBufLocked(l)
+
+	return n, nil
+}
+
+// writeBytes writes to q from b.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+func (q *queue) writeBytes(b []byte, l *lineDiscipline) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	// Write to the wait buffer.
+	q.waitBufAppend(b)
+	q.pushWaitBufLocked(l)
+}
+
+// pushWaitBufLocked fills the queue's read buffer with data from the wait
+// buffer.
+//
+// Preconditions:
+// * l.termiosMu must be held for reading.
+// * q.mu must be locked.
+func (q *queue) pushWaitBufLocked(l *lineDiscipline) int {
+	if q.waitBufLen == 0 {
+		return 0
+	}
+
+	// Move data from the wait to the read buffer.
+	var total int
+	var i int
+	for i = 0; i < len(q.waitBuf); i++ {
+		n := q.transform(l, q, q.waitBuf[i])
+		total += n
+		if n != len(q.waitBuf[i]) {
+			// The read buffer filled up without consuming the
+			// entire buffer.
+			q.waitBuf[i] = q.waitBuf[i][n:]
+			break
+		}
+	}
+
+	// Update wait buffer based on consumed data.
+	q.waitBuf = q.waitBuf[i:]
+	q.waitBufLen -= uint64(total)
+
+	return total
+}
+
+// Precondition: q.mu must be locked.
+func (q *queue) waitBufAppend(b []byte) {
+	q.waitBuf = append(q.waitBuf, b)
+	q.waitBufLen += uint64(len(b))
+}
+
+// LINT.ThenChange(../../fs/tty/queue.go)