1 files changed, 232 insertions, 0 deletions
diff --git a/pkg/sentry/fs/dentry.go b/pkg/sentry/fs/dentry.go
new file mode 100644
index 000000000..d42e8da81
--- /dev/null
+++ b/pkg/sentry/fs/dentry.go
@@ -0,0 +1,232 @@
+// 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 fs
+
+import (
+	"sort"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/device"
+)
+
+// DentAttr is the metadata of a directory entry. It is a subset of StableAttr.
+type DentAttr struct {
+	// Type is the InodeType of an Inode.
+	Type InodeType
+
+	// InodeID uniquely identifies an Inode on a device.
+	InodeID uint64
+}
+
+// GenericDentAttr returns a generic DentAttr where:
+//
+// Type == nt
+// InodeID == the inode id of a new inode on device.
+func GenericDentAttr(nt InodeType, device *device.Device) DentAttr {
+	return DentAttr{
+		Type:    nt,
+		InodeID: device.NextIno(),
+	}
+}
+
+// DentrySerializer serializes a directory entry.
+type DentrySerializer interface {
+	// CopyOut serializes a directory entry based on its name and attributes.
+	CopyOut(name string, attributes DentAttr) error
+
+	// Written returns the number of bytes written.
+	Written() int
+}
+
+// CollectEntriesSerializer copies DentAttrs to Entries. The order in
+// which entries are encountered is preserved in Order.
+type CollectEntriesSerializer struct {
+	Entries map[string]DentAttr
+	Order   []string
+}
+
+// CopyOut implements DentrySerializer.CopyOut.
+func (c *CollectEntriesSerializer) CopyOut(name string, attr DentAttr) error {
+	if c.Entries == nil {
+		c.Entries = make(map[string]DentAttr)
+	}
+	c.Entries[name] = attr
+	c.Order = append(c.Order, name)
+	return nil
+}
+
+// Written implements DentrySerializer.Written.
+func (c *CollectEntriesSerializer) Written() int {
+	return len(c.Entries)
+}
+
+// DirCtx is used by node.Readdir to emit directory entries.  It is not
+// thread-safe.
+type DirCtx struct {
+	// Serializer is used to serialize the node attributes.
+	Serializer DentrySerializer
+
+	// attrs are DentAttrs
+	attrs map[string]DentAttr
+
+	// DirCursor is the directory cursor.
+	// TODO: Once Handles are removed this can just live in the
+	// respective FileOperations implementations and not need to get
+	// plumbed everywhere.
+	DirCursor *string
+}
+
+// DirEmit is called for each directory entry.
+func (c *DirCtx) DirEmit(name string, attr DentAttr) error {
+	if c.Serializer != nil {
+		if err := c.Serializer.CopyOut(name, attr); err != nil {
+			return err
+		}
+	}
+	if c.attrs == nil {
+		c.attrs = make(map[string]DentAttr)
+	}
+	c.attrs[name] = attr
+	return nil
+}
+
+// DentAttrs returns a map of DentAttrs corresponding to the emitted directory
+// entries.
+func (c *DirCtx) DentAttrs() map[string]DentAttr {
+	if c.attrs == nil {
+		c.attrs = make(map[string]DentAttr)
+	}
+	return c.attrs
+}
+
+// GenericReaddir serializes DentAttrs based on a SortedDentryMap that must
+// contain _all_ up-to-date DentAttrs under a directory. If ctx.DirCursor is
+// not nil, it is updated to the name of the last DentAttr that was
+// successfully serialized.
+//
+// Returns the number of entries serialized.
+func GenericReaddir(ctx *DirCtx, s *SortedDentryMap) (int, error) {
+	// Retrieve the next directory entries.
+	var names []string
+	var entries map[string]DentAttr
+	if ctx.DirCursor != nil {
+		names, entries = s.GetNext(*ctx.DirCursor)
+	} else {
+		names, entries = s.GetAll()
+	}
+
+	// Try to serialize each entry.
+	var serialized int
+	for _, name := range names {
+		// Skip "" per POSIX. Skip "." and ".." which will be added by Dirent.Readdir.
+		if name == "" || name == "." || name == ".." {
+			continue
+		}
+
+		// Emit the directory entry.
+		if err := ctx.DirEmit(name, entries[name]); err != nil {
+			// Return potentially a partial serialized count.
+			return serialized, err
+		}
+
+		// We successfully serialized this entry.
+		serialized++
+
+		// Update the cursor with the name of the entry last serialized.
+		if ctx.DirCursor != nil {
+			*ctx.DirCursor = name
+		}
+	}
+
+	// Everything was serialized.
+	return serialized, nil
+}
+
+// SortedDentryMap is a sorted map of names and fs.DentAttr entries.
+type SortedDentryMap struct {
+	// names is always kept in sorted-order.
+	names []string
+
+	// entries maps names to fs.DentAttrs.
+	entries map[string]DentAttr
+}
+
+// NewSortedDentryMap maintains entries in name sorted order.
+func NewSortedDentryMap(entries map[string]DentAttr) *SortedDentryMap {
+	s := &SortedDentryMap{
+		names:   make([]string, 0, len(entries)),
+		entries: entries,
+	}
+	// Don't allow s.entries to be nil, because nil maps arn't Saveable.
+	if s.entries == nil {
+		s.entries = make(map[string]DentAttr)
+	}
+
+	// Collect names from entries and sort them.
+	for name := range s.entries {
+		s.names = append(s.names, name)
+	}
+	sort.Strings(s.names)
+	return s
+}
+
+// GetAll returns all names and entries in s.
+func (s *SortedDentryMap) GetAll() ([]string, map[string]DentAttr) {
+	return s.names, s.entries
+}
+
+// GetNext returns names after cursor in s and all entries.
+func (s *SortedDentryMap) GetNext(cursor string) ([]string, map[string]DentAttr) {
+	i := sort.SearchStrings(s.names, cursor)
+	if i == len(s.names) {
+		return nil, s.entries
+	}
+
+	// Return everything strictly after the cursor.
+	if s.names[i] == cursor {
+		i++
+	}
+	return s.names[i:], s.entries
+}
+
+// Add adds an entry with the given name to the map, preserving sort order.  If
+// name already exists in the map, its entry will be overwritten.
+func (s *SortedDentryMap) Add(name string, entry DentAttr) {
+	if _, ok := s.entries[name]; !ok {
+		// Map does not yet contain an entry with this name.  We must
+		// insert it in s.names at the appropriate spot.
+		i := sort.SearchStrings(s.names, name)
+		s.names = append(s.names, "")
+		copy(s.names[i+1:], s.names[i:])
+		s.names[i] = name
+	}
+	s.entries[name] = entry
+}
+
+// Remove removes an entry with the given name from the map, preserving sort order.
+func (s *SortedDentryMap) Remove(name string) {
+	if _, ok := s.entries[name]; !ok {
+		return
+	}
+	i := sort.SearchStrings(s.names, name)
+	copy(s.names[i:], s.names[i+1:])
+	s.names = s.names[:len(s.names)-1]
+	delete(s.entries, name)
+}
+
+// Contains reports whether the map contains an entry with the given name.
+func (s *SortedDentryMap) Contains(name string) bool {
+	_, ok := s.entries[name]
+	return ok
+}