1 files changed, 282 insertions, 0 deletions
diff --git a/pkg/sentry/vfs/eventfd.go b/pkg/sentry/vfs/eventfd.go
new file mode 100644
index 000000000..f39dacacf
--- /dev/null
+++ b/pkg/sentry/vfs/eventfd.go
@@ -0,0 +1,282 @@
+// Copyright 2020 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 vfs
+
+import (
+	"math"
+	"sync"
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fdnotifier"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// EventFileDescription implements FileDescriptionImpl for file-based event
+// notification (eventfd). Eventfds are usually internal to the Sentry but in
+// certain situations they may be converted into a host-backed eventfd.
+type EventFileDescription struct {
+	vfsfd FileDescription
+	FileDescriptionDefaultImpl
+	DentryMetadataFileDescriptionImpl
+
+	// queue is used to notify interested parties when the event object
+	// becomes readable or writable.
+	queue waiter.Queue `state:"zerovalue"`
+
+	// mu protects the fields below.
+	mu sync.Mutex `state:"nosave"`
+
+	// val is the current value of the event counter.
+	val uint64
+
+	// semMode specifies whether the event is in "semaphore" mode.
+	semMode bool
+
+	// hostfd indicates whether this eventfd is passed through to the host.
+	hostfd int
+}
+
+var _ FileDescriptionImpl = (*EventFileDescription)(nil)
+
+// NewEventFD creates a new event fd.
+func (vfs *VirtualFilesystem) NewEventFD(initVal uint64, semMode bool, flags uint32) (*FileDescription, error) {
+	vd := vfs.NewAnonVirtualDentry("[eventfd]")
+	defer vd.DecRef()
+	efd := &EventFileDescription{
+		val:     initVal,
+		semMode: semMode,
+		hostfd:  -1,
+	}
+	if err := efd.vfsfd.Init(efd, flags, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{
+		UseDentryMetadata: true,
+		DenyPRead:         true,
+		DenyPWrite:        true,
+	}); err != nil {
+		return nil, err
+	}
+	return &efd.vfsfd, nil
+}
+
+// HostFD returns the host eventfd associated with this event.
+func (efd *EventFileDescription) HostFD() (int, error) {
+	efd.mu.Lock()
+	defer efd.mu.Unlock()
+	if efd.hostfd >= 0 {
+		return efd.hostfd, nil
+	}
+
+	flags := linux.EFD_NONBLOCK
+	if efd.semMode {
+		flags |= linux.EFD_SEMAPHORE
+	}
+
+	fd, _, errno := syscall.Syscall(syscall.SYS_EVENTFD2, uintptr(efd.val), uintptr(flags), 0)
+	if errno != 0 {
+		return -1, errno
+	}
+
+	if err := fdnotifier.AddFD(int32(fd), &efd.queue); err != nil {
+		if closeErr := syscall.Close(int(fd)); closeErr != nil {
+			log.Warningf("close(%d) eventfd failed: %v", fd, closeErr)
+		}
+		return -1, err
+	}
+
+	efd.hostfd = int(fd)
+	return efd.hostfd, nil
+}
+
+// Release implements FileDescriptionImpl.Release()
+func (efd *EventFileDescription) Release() {
+	efd.mu.Lock()
+	defer efd.mu.Unlock()
+	if efd.hostfd >= 0 {
+		fdnotifier.RemoveFD(int32(efd.hostfd))
+		if closeErr := syscall.Close(int(efd.hostfd)); closeErr != nil {
+			log.Warningf("close(%d) eventfd failed: %v", efd.hostfd, closeErr)
+		}
+		efd.hostfd = -1
+	}
+}
+
+// Read implements FileDescriptionImpl.Read.
+func (efd *EventFileDescription) Read(ctx context.Context, dst usermem.IOSequence, _ ReadOptions) (int64, error) {
+	if dst.NumBytes() < 8 {
+		return 0, syscall.EINVAL
+	}
+	if err := efd.read(ctx, dst); err != nil {
+		return 0, err
+	}
+	return 8, nil
+}
+
+// Write implements FileDescriptionImpl.Write.
+func (efd *EventFileDescription) Write(ctx context.Context, src usermem.IOSequence, _ WriteOptions) (int64, error) {
+	if src.NumBytes() < 8 {
+		return 0, syscall.EINVAL
+	}
+	if err := efd.write(ctx, src); err != nil {
+		return 0, err
+	}
+	return 8, nil
+}
+
+// Preconditions: Must be called with efd.mu locked.
+func (efd *EventFileDescription) hostReadLocked(ctx context.Context, dst usermem.IOSequence) error {
+	var buf [8]byte
+	if _, err := syscall.Read(efd.hostfd, buf[:]); err != nil {
+		if err == syscall.EWOULDBLOCK {
+			return syserror.ErrWouldBlock
+		}
+		return err
+	}
+	_, err := dst.CopyOut(ctx, buf[:])
+	return err
+}
+
+func (efd *EventFileDescription) read(ctx context.Context, dst usermem.IOSequence) error {
+	efd.mu.Lock()
+	if efd.hostfd >= 0 {
+		defer efd.mu.Unlock()
+		return efd.hostReadLocked(ctx, dst)
+	}
+
+	// We can't complete the read if the value is currently zero.
+	if efd.val == 0 {
+		efd.mu.Unlock()
+		return syserror.ErrWouldBlock
+	}
+
+	// Update the value based on the mode the event is operating in.
+	var val uint64
+	if efd.semMode {
+		val = 1
+		// Consistent with Linux, this is done even if writing to memory fails.
+		efd.val--
+	} else {
+		val = efd.val
+		efd.val = 0
+	}
+
+	efd.mu.Unlock()
+
+	// Notify writers. We do this even if we were already writable because
+	// it is possible that a writer is waiting to write the maximum value
+	// to the event.
+	efd.queue.Notify(waiter.EventOut)
+
+	var buf [8]byte
+	usermem.ByteOrder.PutUint64(buf[:], val)
+	_, err := dst.CopyOut(ctx, buf[:])
+	return err
+}
+
+// Preconditions: Must be called with efd.mu locked.
+func (efd *EventFileDescription) hostWriteLocked(val uint64) error {
+	var buf [8]byte
+	usermem.ByteOrder.PutUint64(buf[:], val)
+	_, err := syscall.Write(efd.hostfd, buf[:])
+	if err == syscall.EWOULDBLOCK {
+		return syserror.ErrWouldBlock
+	}
+	return err
+}
+
+func (efd *EventFileDescription) write(ctx context.Context, src usermem.IOSequence) error {
+	var buf [8]byte
+	if _, err := src.CopyIn(ctx, buf[:]); err != nil {
+		return err
+	}
+	val := usermem.ByteOrder.Uint64(buf[:])
+
+	return efd.Signal(val)
+}
+
+// Signal is an internal function to signal the event fd.
+func (efd *EventFileDescription) Signal(val uint64) error {
+	if val == math.MaxUint64 {
+		return syscall.EINVAL
+	}
+
+	efd.mu.Lock()
+
+	if efd.hostfd >= 0 {
+		defer efd.mu.Unlock()
+		return efd.hostWriteLocked(val)
+	}
+
+	// We only allow writes that won't cause the value to go over the max
+	// uint64 minus 1.
+	if val > math.MaxUint64-1-efd.val {
+		efd.mu.Unlock()
+		return syserror.ErrWouldBlock
+	}
+
+	efd.val += val
+	efd.mu.Unlock()
+
+	// Always trigger a notification.
+	efd.queue.Notify(waiter.EventIn)
+
+	return nil
+}
+
+// Readiness implements waiter.Waitable.Readiness.
+func (efd *EventFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
+	efd.mu.Lock()
+	defer efd.mu.Unlock()
+
+	if efd.hostfd >= 0 {
+		return fdnotifier.NonBlockingPoll(int32(efd.hostfd), mask)
+	}
+
+	ready := waiter.EventMask(0)
+	if efd.val > 0 {
+		ready |= waiter.EventIn
+	}
+
+	if efd.val < math.MaxUint64-1 {
+		ready |= waiter.EventOut
+	}
+
+	return mask & ready
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (efd *EventFileDescription) EventRegister(entry *waiter.Entry, mask waiter.EventMask) {
+	efd.queue.EventRegister(entry, mask)
+
+	efd.mu.Lock()
+	defer efd.mu.Unlock()
+	if efd.hostfd >= 0 {
+		fdnotifier.UpdateFD(int32(efd.hostfd))
+	}
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (efd *EventFileDescription) EventUnregister(entry *waiter.Entry) {
+	efd.queue.EventUnregister(entry)
+
+	efd.mu.Lock()
+	defer efd.mu.Unlock()
+	if efd.hostfd >= 0 {
+		fdnotifier.UpdateFD(int32(efd.hostfd))
+	}
+}