ext: inode implementations.

PiperOrigin-RevId: 260624470

14 files changed, 587 insertions, 118 deletions

diff --git a/pkg/sentry/fs/ext/BUILD b/pkg/sentry/fs/ext/BUILD
index 2c15875f5..60f6debaf 100644
--- a/pkg/sentry/fs/ext/BUILD
+++ b/pkg/sentry/fs/ext/BUILD
@@ -1,14 +1,35 @@
 package(licenses = ["notice"])
 
 load("//tools/go_stateify:defs.bzl", "go_library", "go_test")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
+
+go_template_instance(
+    name = "dentry_list",
+    out = "dentry_list.go",
+    package = "ext",
+    prefix = "dentry",
+    template = "//pkg/ilist:generic_list",
+    types = {
+        "Element": "*dentry",
+        "Linker": "*dentry",
+    },
+)
 
 go_library(
     name = "ext",
     srcs = [
+        "block_map_file.go",
         "dentry.go",
+        "dentry_list.go",
+        "directory.go",
         "ext.go",
+        "extent_file.go",
         "filesystem.go",
+        "inline_file.go",
         "inode.go",
+        "named_pipe.go",
+        "regular_file.go",
+        "symlink.go",
         "utils.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext",
@@ -17,8 +38,11 @@ go_library(
         "//pkg/abi/linux",
         "//pkg/binary",
         "//pkg/sentry/context",
+        "//pkg/sentry/fs",
         "//pkg/sentry/fs/ext/disklayout",
         "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/pipe",
+        "//pkg/sentry/usermem",
         "//pkg/sentry/vfs",
         "//pkg/syserror",
     ],
diff --git a/pkg/sentry/fs/ext/block_map_file.go b/pkg/sentry/fs/ext/block_map_file.go
new file mode 100644
index 000000000..eb0b35e36
--- /dev/null
+++ b/pkg/sentry/fs/ext/block_map_file.go
@@ -0,0 +1,61 @@
+// 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"
+)
+
+// blockMapFile is a type of regular file which uses direct/indirect block
+// addressing to store file data. This was deprecated in ext4.
+type blockMapFile struct {
+	regFile regularFile
+
+	// fileToPhysBlks maps the file block numbers to the physical block numbers.
+	// the physical block number for the (i)th file block is stored in the (i)th
+	// index. This is initialized (at max) with the first 12 entries. The rest
+	// have to be read in from disk when required.
+	fileToPhysBlks []uint32
+}
+
+// Compiles only if blockMapFile implements fileReader.
+var _ fileReader = (*blockMapFile)(nil)
+
+// Read implements fileReader.getFileReader.
+func (f *blockMapFile) getFileReader(dev io.ReadSeeker, blkSize uint64, offset uint64) io.Reader {
+	panic("unimplemented")
+}
+
+// newBlockMapFile is the blockMapFile constructor. It initializes the file to
+// physical blocks map with (at most) the first 12 (direct) blocks.
+func newBlockMapFile(blkSize uint64, regFile regularFile) (*blockMapFile, error) {
+	file := &blockMapFile{regFile: regFile}
+	file.regFile.impl = file
+
+	toFill := uint64(12)
+	blksUsed := regFile.blksUsed(blkSize)
+	if blksUsed < toFill {
+		toFill = blksUsed
+	}
+
+	blkMap := regFile.inode.diskInode.Data()
+	file.fileToPhysBlks = make([]uint32, toFill)
+	for i := uint64(0); i < toFill; i++ {
+		binary.Unmarshal(blkMap[i*4:(i+1)*4], binary.LittleEndian, &file.fileToPhysBlks[i])
+	}
+	return file, nil
+}
diff --git a/pkg/sentry/fs/ext/dentry.go b/pkg/sentry/fs/ext/dentry.go
index 054fb42b6..19c9b3b2d 100644
--- a/pkg/sentry/fs/ext/dentry.go
+++ b/pkg/sentry/fs/ext/dentry.go
@@ -26,6 +26,8 @@ type dentry struct {
 	// share a single non-directory Inode (with hard links). inode is
 	// immutable.
 	inode *inode
+	// dentryEntry links Dentries into their parent directory.childList.
+	dentryEntry
 }
 
 // Compiles only if dentry implements vfs.DentryImpl.
diff --git a/pkg/sentry/fs/ext/directory.go b/pkg/sentry/fs/ext/directory.go
new file mode 100644
index 000000000..ab2b59e44
--- /dev/null
+++ b/pkg/sentry/fs/ext/directory.go
@@ -0,0 +1,36 @@
+// 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
+
+// directory represents a directory inode. It holds the childList in memory.
+type directory struct {
+	inode inode
+
+	// childList is a list containing (1) child Dentries and (2) fake Dentries
+	// (with inode == nil) that represent the iteration position of
+	// directoryFDs. childList is used to support directoryFD.IterDirents()
+	// efficiently. childList is immutable.
+	childList dentryList
+
+	// TODO(b/134676337): Add directory navigators.
+}
+
+// newDirectroy is the directory constructor.
+func newDirectroy(inode inode) *directory {
+	// TODO(b/134676337): initialize childList.
+	file := &directory{inode: inode}
+	file.inode.impl = file
+	return file
+}
diff --git a/pkg/sentry/fs/ext/ext.go b/pkg/sentry/fs/ext/ext.go
index 10e235fb1..2380f15da 100644
--- a/pkg/sentry/fs/ext/ext.go
+++ b/pkg/sentry/fs/ext/ext.go
@@ -88,7 +88,7 @@ func (fstype filesystemType) NewFilesystem(ctx context.Context, creds *auth.Cred
 		return nil, nil, err
 	}
 
-	rootInode, err := fs.getOrCreateInode(disklayout.RootDirInode)
+	rootInode, err := fs.getOrCreateInode(ctx, disklayout.RootDirInode)
 	if err != nil {
 		return nil, nil, err
 	}
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
+}
diff --git a/pkg/sentry/fs/ext/extent_test.go b/pkg/sentry/fs/ext/extent_test.go
index b3f342c8e..01251d0a7 100644
--- a/pkg/sentry/fs/ext/extent_test.go
+++ b/pkg/sentry/fs/ext/extent_test.go
@@ -47,7 +47,13 @@ import (
 func TestExtentTree(t *testing.T) {
 	blkSize := uint64(64) // No block has more than 1 header + 4 entries.
 	mockDisk := make([]byte, blkSize*10)
-	mockInode := &inode{diskInode: &disklayout.InodeNew{}}
+	mockExtentFile := extentFile{
+		regFile: regularFile{
+			inode: inode{
+				diskInode: &disklayout.InodeNew{},
+			},
+		},
+	}
 
 	node3 := &disklayout.ExtentNode{
 		Header: disklayout.ExtentHeader{
@@ -138,15 +144,15 @@ func TestExtentTree(t *testing.T) {
 		},
 	}
 
-	writeTree(mockInode, mockDisk, node0, blkSize)
+	writeTree(&mockExtentFile.regFile.inode, mockDisk, node0, blkSize)
 
 	r := bytes.NewReader(mockDisk)
-	if err := mockInode.buildExtTree(r, blkSize); err != nil {
+	if err := mockExtentFile.buildExtTree(r, blkSize); err != nil {
 		t.Fatalf("inode.buildExtTree failed: %v", err)
 	}
 
 	opt := cmpopts.IgnoreUnexported(disklayout.ExtentIdx{}, disklayout.ExtentHeader{})
-	if diff := cmp.Diff(mockInode.root, node0, opt); diff != "" {
+	if diff := cmp.Diff(&mockExtentFile.root, node0, opt); diff != "" {
 		t.Errorf("extent tree mismatch (-want +got):\n%s", diff)
 	}
 }
diff --git a/pkg/sentry/fs/ext/filesystem.go b/pkg/sentry/fs/ext/filesystem.go
index 7150e75a5..32ca11026 100644
--- a/pkg/sentry/fs/ext/filesystem.go
+++ b/pkg/sentry/fs/ext/filesystem.go
@@ -70,12 +70,12 @@ var _ vfs.FilesystemImpl = (*filesystem)(nil)
 // It creates a new one with the given inode number if one does not exist.
 //
 // Preconditions: must be holding fs.mu.
-func (fs *filesystem) getOrCreateInode(inodeNum uint32) (*inode, error) {
+func (fs *filesystem) getOrCreateInode(ctx context.Context, inodeNum uint32) (*inode, error) {
 	if in, ok := fs.inodeCache[inodeNum]; ok {
 		return in, nil
 	}
 
-	in, err := newInode(fs.dev, fs.sb, fs.bgs, inodeNum)
+	in, err := newInode(ctx, fs.dev, fs.sb, fs.bgs, inodeNum)
 	if err != nil {
 		return nil, err
 	}
diff --git a/pkg/sentry/fs/ext/inline_file.go b/pkg/sentry/fs/ext/inline_file.go
new file mode 100644
index 000000000..dd93ee2e1
--- /dev/null
+++ b/pkg/sentry/fs/ext/inline_file.go
@@ -0,0 +1,65 @@
+// 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"
+)
+
+// inlineFile is a type of regular file. All the data here is stored in the
+// inode.Data() array.
+type inlineFile struct {
+	regFile regularFile
+}
+
+// Compiles only if inlineFile implements fileReader.
+var _ fileReader = (*inlineFile)(nil)
+
+// getFileReader implements fileReader.getFileReader.
+func (f *inlineFile) getFileReader(_ io.ReadSeeker, _ uint64, offset uint64) io.Reader {
+	diskInode := f.regFile.inode.diskInode
+	return &inlineReader{offset: offset, data: diskInode.Data()[:diskInode.Size()]}
+}
+
+// newInlineFile is the inlineFile constructor.
+func newInlineFile(regFile regularFile) *inlineFile {
+	file := &inlineFile{regFile: regFile}
+	file.regFile.impl = file
+	return file
+}
+
+// inlineReader implements io.Reader which can read the underlying data.
+type inlineReader struct {
+	offset uint64
+	data   []byte
+}
+
+// Compiles only if inlineReader implements io.Reader.
+var _ io.Reader = (*inlineReader)(nil)
+
+// Read implements io.Reader.Read.
+func (r *inlineReader) Read(dst []byte) (int, error) {
+	if len(dst) == 0 {
+		return 0, nil
+	}
+
+	if int(r.offset) >= len(r.data) {
+		return 0, io.EOF
+	}
+
+	n := copy(dst, r.data[r.offset:])
+	r.offset += uint64(n)
+	return n, nil
+}
diff --git a/pkg/sentry/fs/ext/inode.go b/pkg/sentry/fs/ext/inode.go
index df1ea0bda..7d2a445fb 100644
--- a/pkg/sentry/fs/ext/inode.go
+++ b/pkg/sentry/fs/ext/inode.go
@@ -18,12 +18,26 @@ import (
 	"io"
 	"sync/atomic"
 
-	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/context"
 	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // inode represents an ext inode.
+//
+// inode uses the same inheritance pattern that pkg/sentry/vfs structures use.
+// This has been done to increase memory locality.
+//
+// Implementations:
+//    inode --
+//           |-- pipe
+//           |-- dir
+//           |-- symlink
+//           |-- regular--
+//                       |-- extent file
+//                       |-- block map file
+//                       |-- inline file
 type inode struct {
 	// refs is a reference count. refs is accessed using atomic memory operations.
 	refs int64
@@ -35,9 +49,9 @@ type inode struct {
 	// diskInode gives us access to the inode struct on disk. Immutable.
 	diskInode disklayout.Inode
 
-	// root is the root extent node. This lives in the 60 byte diskInode.Blocks().
-	// Immutable. Nil if the inode does not use extents.
-	root *disklayout.ExtentNode
+	// This is immutable. The first field of the implementations must have inode
+	// as the first field to ensure temporality.
+	impl interface{}
 }
 
 // incRef increments the inode ref count.
@@ -74,17 +88,17 @@ func (in *inode) decRef(fs *filesystem) {
 // inodes based on the absolute inode number on disk.
 //
 // Preconditions: Must hold the mutex of the filesystem containing dev.
-func newInode(dev io.ReadSeeker, sb disklayout.SuperBlock, bgs []disklayout.BlockGroup, inodeNum uint32) (*inode, error) {
+func newInode(ctx context.Context, dev io.ReadSeeker, sb disklayout.SuperBlock, bgs []disklayout.BlockGroup, inodeNum uint32) (*inode, error) {
 	if inodeNum == 0 {
 		panic("inode number 0 on ext filesystems is not possible")
 	}
 
-	in := &inode{refs: 1, inodeNum: inodeNum}
 	inodeRecordSize := sb.InodeSize()
+	var diskInode disklayout.Inode
 	if inodeRecordSize == disklayout.OldInodeSize {
-		in.diskInode = &disklayout.InodeOld{}
+		diskInode = &disklayout.InodeOld{}
 	} else {
-		in.diskInode = &disklayout.InodeNew{}
+		diskInode = &disklayout.InodeNew{}
 	}
 
 	// Calculate where the inode is actually placed.
@@ -93,16 +107,38 @@ func newInode(dev io.ReadSeeker, sb disklayout.SuperBlock, bgs []disklayout.Bloc
 	inodeTableOff := bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
 	inodeOff := inodeTableOff + uint64(uint32(inodeRecordSize)*getBGOff(inodeNum, inodesPerGrp))
 
-	// Read it from disk and figure out which type of inode this is.
-	if err := readFromDisk(dev, int64(inodeOff), in.diskInode); err != nil {
+	if err := readFromDisk(dev, int64(inodeOff), diskInode); err != nil {
 		return nil, err
 	}
 
-	if in.diskInode.Flags().Extents {
-		in.buildExtTree(dev, blkSize)
+	// Build the inode based on its type.
+	inode := inode{
+		refs:      1,
+		inodeNum:  inodeNum,
+		diskInode: diskInode,
 	}
 
-	return in, nil
+	switch diskInode.Mode().FileType() {
+	case linux.ModeSymlink:
+		f, err := newSymlink(dev, blkSize, inode)
+		if err != nil {
+			return nil, err
+		}
+		return &f.inode, nil
+	case linux.ModeRegular:
+		f, err := newRegularFile(dev, blkSize, inode)
+		if err != nil {
+			return nil, err
+		}
+		return &f.inode, nil
+	case linux.ModeDirectory:
+		return &newDirectroy(inode).inode, nil
+	case linux.ModeNamedPipe:
+		return &newNamedPipe(ctx, inode).inode, nil
+	default:
+		// TODO(b/134676337): Return appropriate errors for sockets and devices.
+		return nil, syserror.EINVAL
+	}
 }
 
 // getBGNum returns the block group number that a given inode belongs to.
@@ -115,95 +151,3 @@ func getBGNum(inodeNum uint32, inodesPerGrp uint32) uint32 {
 func getBGOff(inodeNum uint32, inodesPerGrp uint32) uint32 {
 	return (inodeNum - 1) % inodesPerGrp
 }
-
-// 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 (in *inode) buildExtTree(dev io.ReadSeeker, blkSize uint64) error {
-	rootNodeData := in.diskInode.Data()
-
-	var rootHeader disklayout.ExtentHeader
-	binary.Unmarshal(rootNodeData[:disklayout.ExtentStructsSize], binary.LittleEndian, &rootHeader)
-
-	// Root node can not have more than 4 entries: 60 bytes = 1 header + 4 entries.
-	if rootHeader.NumEntries > 4 {
-		// read(2) specifies that EINVAL should be returned if the file is unsuitable
-		// for reading.
-		return syserror.EINVAL
-	}
-
-	rootEntries := make([]disklayout.ExtentEntryPair, rootHeader.NumEntries)
-	for i, off := uint16(0), disklayout.ExtentStructsSize; i < rootHeader.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
-		var curEntry disklayout.ExtentEntry
-		if rootHeader.Height == 0 {
-			// Leaf node.
-			curEntry = &disklayout.Extent{}
-		} else {
-			// Internal node.
-			curEntry = &disklayout.ExtentIdx{}
-		}
-		binary.Unmarshal(rootNodeData[off:off+disklayout.ExtentStructsSize], binary.LittleEndian, curEntry)
-		rootEntries[i].Entry = curEntry
-	}
-
-	// If this node is internal, perform DFS.
-	if rootHeader.Height > 0 {
-		for i := uint16(0); i < rootHeader.NumEntries; i++ {
-			var err error
-			if rootEntries[i].Node, err = buildExtTreeFromDisk(dev, rootEntries[i].Entry, blkSize); err != nil {
-				return err
-			}
-		}
-	}
-
-	in.root = &disklayout.ExtentNode{rootHeader, rootEntries}
-	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
-	if err := readFromDisk(dev, int64(off), &header); 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{}
-		}
-
-		if err := readFromDisk(dev, int64(off), curEntry); 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
-}
diff --git a/pkg/sentry/fs/ext/named_pipe.go b/pkg/sentry/fs/ext/named_pipe.go
new file mode 100644
index 000000000..0f3af1b53
--- /dev/null
+++ b/pkg/sentry/fs/ext/named_pipe.go
@@ -0,0 +1,40 @@
+// 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 (
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/pipe"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+)
+
+// namedPipe represents a named pipe inode. It is currently just a wrapper
+// around pkg/sentry/kernel/pipe.
+type namedPipe struct {
+	inode inode
+
+	p        *pipe.Pipe
+	inodeOps fs.InodeOperations
+}
+
+// newNamedPipe is the namedPipe constructor.
+func newNamedPipe(ctx context.Context, inode inode) *namedPipe {
+	file := &namedPipe{inode: inode}
+	file.inode.impl = file
+	file.p = pipe.NewPipe(ctx, true /* isNamed */, pipe.DefaultPipeSize, usermem.PageSize)
+	file.inodeOps = pipe.NewInodeOperations(ctx, fs.FilePermsFromMode(file.inode.diskInode.Mode()), file.p)
+	return file
+}
diff --git a/pkg/sentry/fs/ext/regular_file.go b/pkg/sentry/fs/ext/regular_file.go
new file mode 100644
index 000000000..9bf39acfe
--- /dev/null
+++ b/pkg/sentry/fs/ext/regular_file.go
@@ -0,0 +1,90 @@
+// 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"
+)
+
+// fileReader is used to abstact away the complexity of how the file data is
+// stored under the hood. Provides a method to get a file reader which can be
+// used to read file data without worrying about how it is organized on disk.
+type fileReader interface {
+
+	// getFileReader returns a Reader implementation which can be used to read a
+	// file. It abstracts away the complexity of how the file is actually
+	// organized on disk. The reader is initialized with the passed offset.
+	//
+	// This reader is not meant to be retained across Read operations as it needs
+	// to be reinitialized with the correct offset for every Read.
+	//
+	// Precondition: Must hold the mutex of the filesystem containing dev while
+	//               using the Reader.
+	getFileReader(dev io.ReadSeeker, blkSize uint64, offset uint64) io.Reader
+}
+
+// regularFile represents a regular file's inode. This too follows the
+// inheritance pattern prevelant in the vfs layer described in
+// pkg/sentry/vfs/README.md.
+type regularFile struct {
+	inode inode
+
+	// This is immutable. The first field of fileReader implementations must be
+	// regularFile to ensure temporality.
+	impl fileReader
+}
+
+// newRegularFile is the regularFile constructor. It figures out what kind of
+// file this is and initializes the fileReader.
+//
+// Preconditions: Must hold the mutex of the filesystem containing dev.
+func newRegularFile(dev io.ReadSeeker, blkSize uint64, inode inode) (*regularFile, error) {
+	regFile := regularFile{
+		inode: inode,
+	}
+
+	inodeFlags := inode.diskInode.Flags()
+
+	if inodeFlags.Extents {
+		file, err := newExtentFile(dev, blkSize, regFile)
+		if err != nil {
+			return nil, err
+		}
+
+		file.regFile.inode.impl = &file.regFile
+		return &file.regFile, nil
+	}
+
+	if inodeFlags.Inline {
+		if inode.diskInode.Size() > 60 {
+			panic("ext fs: inline file larger than 60 bytes")
+		}
+
+		file := newInlineFile(regFile)
+		file.regFile.inode.impl = &file.regFile
+		return &file.regFile, nil
+	}
+
+	file, err := newBlockMapFile(blkSize, regFile)
+	if err != nil {
+		return nil, err
+	}
+	file.regFile.inode.impl = &file.regFile
+	return &file.regFile, nil
+}
+
+func (f *regularFile) blksUsed(blkSize uint64) uint64 {
+	return (f.inode.diskInode.Size() + blkSize - 1) / blkSize
+}
diff --git a/pkg/sentry/fs/ext/symlink.go b/pkg/sentry/fs/ext/symlink.go
new file mode 100644
index 000000000..0ed67c0e4
--- /dev/null
+++ b/pkg/sentry/fs/ext/symlink.go
@@ -0,0 +1,59 @@
+// 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/syserror"
+)
+
+// symlink represents a symlink inode.
+type symlink struct {
+	inode  inode
+	target string // immutable
+}
+
+// newSymlink is the symlink constructor. It reads out the symlink target from
+// the inode (however it might have been stored).
+//
+// Preconditions: Must hold the mutex of the filesystem containing dev.
+func newSymlink(dev io.ReadSeeker, blkSize uint64, inode inode) (*symlink, error) {
+	var file *symlink
+	var link []byte
+
+	// If the symlink target is lesser than 60 bytes, its stores in inode.Data().
+	// Otherwise either extents or block maps will be used to store the link.
+	size := inode.diskInode.Size()
+	if size < 60 {
+		link = inode.diskInode.Data()[:size]
+	} else {
+		// Create a regular file out of this inode and read out the target.
+		regFile, err := newRegularFile(dev, blkSize, inode)
+		if err != nil {
+			return nil, err
+		}
+
+		link = make([]byte, size)
+		reader := regFile.impl.getFileReader(dev, blkSize, 0)
+		if _, err := io.ReadFull(reader, link); err != nil {
+			return nil, syserror.EIO
+		}
+	}
+
+	file = &symlink{inode: inode, target: string(link)}
+	file.inode.impl = file
+	return file, nil
+}
diff --git a/pkg/sentry/fs/ext/utils.go b/pkg/sentry/fs/ext/utils.go
index 3472c5fa8..8790c7778 100644
--- a/pkg/sentry/fs/ext/utils.go
+++ b/pkg/sentry/fs/ext/utils.go
@@ -76,12 +76,7 @@ func blockGroupsCount(sb disklayout.SuperBlock) uint64 {
 	blocksPerGroup := uint64(sb.BlocksPerGroup())
 
 	// Round up the result. float64 can compromise precision so do it manually.
-	bgCount := blocksCount / blocksPerGroup
-	if blocksCount%blocksPerGroup != 0 {
-		bgCount++
-	}
-
-	return bgCount
+	return (blocksCount + blocksPerGroup - 1) / blocksPerGroup
 }
 
 // readBlockGroups reads the block group descriptor table from block group 0 in