1 files changed, 147 insertions, 0 deletions
diff --git a/pkg/sentry/fs/ext/extent_file.go b/pkg/sentry/fs/ext/extent_file.go
new file mode 100644
index 000000000..86583881d
--- /dev/null
+++ b/pkg/sentry/fs/ext/extent_file.go
@@ -0,0 +1,147 @@
+// Copyright 2019 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 ext
+
+import (
+	"io"
+
+	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// extentFile is a type of regular file which uses extents to store file data.
+type extentFile struct {
+	regFile regularFile
+
+	// root is the root extent node. This lives in the 60 byte diskInode.Data().
+	// Immutable.
+	root disklayout.ExtentNode
+}
+
+// Compiles only if extentFile implements fileReader.
+var _ fileReader = (*extentFile)(nil)
+
+// Read implements fileReader.getFileReader.
+func (f *extentFile) getFileReader(dev io.ReadSeeker, blkSize uint64, offset uint64) io.Reader {
+	panic("unimplemented")
+}
+
+// newExtentFile is the extent file constructor. It reads the entire extent
+// tree into memory.
+//
+// Preconditions: Must hold the mutex of the filesystem containing dev.
+// TODO(b/134676337): Build extent tree on demand to reduce memory usage.
+func newExtentFile(dev io.ReadSeeker, blkSize uint64, regFile regularFile) (*extentFile, error) {
+	file := &extentFile{regFile: regFile}
+	file.regFile.impl = file
+	err := file.buildExtTree(dev, blkSize)
+	if err != nil {
+		return nil, err
+	}
+	return file, nil
+}
+
+// buildExtTree builds the extent tree by reading it from disk by doing
+// running a simple DFS. It first reads the root node from the inode struct in
+// memory. Then it recursively builds the rest of the tree by reading it off
+// disk.
+//
+// Preconditions:
+//   - Must hold the mutex of the filesystem containing dev.
+//   - Inode flag InExtents must be set.
+func (f *extentFile) buildExtTree(dev io.ReadSeeker, blkSize uint64) error {
+	rootNodeData := f.regFile.inode.diskInode.Data()
+
+	binary.Unmarshal(rootNodeData[:disklayout.ExtentStructsSize], binary.LittleEndian, &f.root.Header)
+
+	// Root node can not have more than 4 entries: 60 bytes = 1 header + 4 entries.
+	if f.root.Header.NumEntries > 4 {
+		// read(2) specifies that EINVAL should be returned if the file is unsuitable
+		// for reading.
+		return syserror.EINVAL
+	}
+
+	f.root.Entries = make([]disklayout.ExtentEntryPair, f.root.Header.NumEntries)
+	for i, off := uint16(0), disklayout.ExtentStructsSize; i < f.root.Header.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
+		var curEntry disklayout.ExtentEntry
+		if f.root.Header.Height == 0 {
+			// Leaf node.
+			curEntry = &disklayout.Extent{}
+		} else {
+			// Internal node.
+			curEntry = &disklayout.ExtentIdx{}
+		}
+		binary.Unmarshal(rootNodeData[off:off+disklayout.ExtentStructsSize], binary.LittleEndian, curEntry)
+		f.root.Entries[i].Entry = curEntry
+	}
+
+	// If this node is internal, perform DFS.
+	if f.root.Header.Height > 0 {
+		for i := uint16(0); i < f.root.Header.NumEntries; i++ {
+			var err error
+			if f.root.Entries[i].Node, err = buildExtTreeFromDisk(dev, f.root.Entries[i].Entry, blkSize); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+// buildExtTreeFromDisk reads the extent tree nodes from disk and recursively
+// builds the tree. Performs a simple DFS. It returns the ExtentNode pointed to
+// by the ExtentEntry.
+//
+// Preconditions: Must hold the mutex of the filesystem containing dev.
+func buildExtTreeFromDisk(dev io.ReadSeeker, entry disklayout.ExtentEntry, blkSize uint64) (*disklayout.ExtentNode, error) {
+	var header disklayout.ExtentHeader
+	off := entry.PhysicalBlock() * blkSize
+	err := readFromDisk(dev, int64(off), &header)
+	if err != nil {
+		return nil, err
+	}
+
+	entries := make([]disklayout.ExtentEntryPair, header.NumEntries)
+	for i, off := uint16(0), off+disklayout.ExtentStructsSize; i < header.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
+		var curEntry disklayout.ExtentEntry
+		if header.Height == 0 {
+			// Leaf node.
+			curEntry = &disklayout.Extent{}
+		} else {
+			// Internal node.
+			curEntry = &disklayout.ExtentIdx{}
+		}
+
+		err := readFromDisk(dev, int64(off), curEntry)
+		if err != nil {
+			return nil, err
+		}
+		entries[i].Entry = curEntry
+	}
+
+	// If this node is internal, perform DFS.
+	if header.Height > 0 {
+		for i := uint16(0); i < header.NumEntries; i++ {
+			var err error
+			entries[i].Node, err = buildExtTreeFromDisk(dev, entries[i].Entry, blkSize)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return &disklayout.ExtentNode{header, entries}, nil
+}