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PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 118 insertions, 0 deletions

diff --git a/pkg/sentry/fs/host/descriptor.go b/pkg/sentry/fs/host/descriptor.go
new file mode 100644
index 000000000..613bd06e8
--- /dev/null
+++ b/pkg/sentry/fs/host/descriptor.go
@@ -0,0 +1,118 @@
+// 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 host
+
+import (
+	"fmt"
+	"path"
+	"syscall"
+
+	"gvisor.googlesource.com/gvisor/pkg/log"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+	"gvisor.googlesource.com/gvisor/pkg/waiter/fdnotifier"
+)
+
+// descriptor wraps a host fd.
+type descriptor struct {
+	// donated is true if the host fd was donated by another process.
+	donated bool
+
+	// If origFD >= 0, it is the host fd that this file was
+	// originally created from, which must be available at time
+	// of restore. Only valid if donated is true.
+	origFD int
+
+	// wouldBlock is true if value (below) points to a file that can
+	// return EWOULDBLOCK for operations that would block.
+	wouldBlock bool
+
+	// value is the wrapped host fd. It is never saved or restored
+	// directly. How it is restored depends on whether it was
+	// donated and the fs.MountSource it was originally
+	// opened/created from.
+	value int `state:"nosave"`
+}
+
+// newDescriptor returns a wrapped host file descriptor. On success,
+// the descriptor is registered for event notifications with queue.
+func newDescriptor(fd int, donated bool, saveable bool, wouldBlock bool, queue *waiter.Queue) (*descriptor, error) {
+	ownedFD := fd
+	origFD := -1
+	if saveable {
+		var err error
+		ownedFD, err = syscall.Dup(fd)
+		if err != nil {
+			return nil, err
+		}
+		origFD = fd
+	}
+	if wouldBlock {
+		if err := syscall.SetNonblock(ownedFD, true); err != nil {
+			return nil, err
+		}
+		if err := fdnotifier.AddFD(int32(ownedFD), queue); err != nil {
+			return nil, err
+		}
+	}
+	return &descriptor{
+		donated:    donated,
+		origFD:     origFD,
+		wouldBlock: wouldBlock,
+		value:      ownedFD,
+	}, nil
+}
+
+// initAfterLoad initializes the value of the descriptor after Load.
+func (d *descriptor) initAfterLoad(mo *superOperations, id uint64, queue *waiter.Queue) error {
+	if d.donated {
+		var err error
+		d.value, err = syscall.Dup(d.origFD)
+		if err != nil {
+			return fmt.Errorf("failed to dup restored fd %d: %v", d.origFD, err)
+		}
+	} else {
+		name, ok := mo.inodeMappings[id]
+		if !ok {
+			return fmt.Errorf("failed to find path for inode number %d", id)
+		}
+		fullpath := path.Join(mo.root, name)
+
+		var err error
+		d.value, err = open(nil, fullpath)
+		if err != nil {
+			return fmt.Errorf("failed to open %q: %v", fullpath, err)
+		}
+	}
+	if d.wouldBlock {
+		if err := syscall.SetNonblock(d.value, true); err != nil {
+			return err
+		}
+		if err := fdnotifier.AddFD(int32(d.value), queue); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Release releases all resources held by descriptor.
+func (d *descriptor) Release() {
+	if d.wouldBlock {
+		fdnotifier.RemoveFD(int32(d.value))
+	}
+	if err := syscall.Close(d.value); err != nil {
+		log.Warningf("error closing fd %d: %v", d.value, err)
+	}
+	d.value = -1
+}