ext: Added extent tree building logic.

PiperOrigin-RevId: 259628657

1 files changed, 184 insertions, 0 deletions

diff --git a/pkg/sentry/fs/ext/extent_test.go b/pkg/sentry/fs/ext/extent_test.go
new file mode 100644
index 000000000..c8c52f836
--- /dev/null
+++ b/pkg/sentry/fs/ext/extent_test.go
@@ -0,0 +1,184 @@
+// 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 (
+	"bytes"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+)
+
+// TestExtentTree tests the extent tree building logic.
+//
+// Test tree:
+//            0.{Head}[Idx][Idx]
+//                     /     \
+//                    /       \
+//      1.{Head}[Ext][Ext]  2.{Head}[Idx]
+//               /    |               \
+//           [Phy]  [Phy, Phy]    3.{Head}[Ext]
+//                                          |
+//                                    [Phy, Phy, Phy]
+//
+// Legend:
+//   - Head = ExtentHeader
+//   - Idx  = ExtentIdx
+//   - Ext  = Extent
+//   - Phy  = Physical Block
+//
+// Please note that ext4 might not construct extent trees looking like this.
+// This is purely for testing the tree traversal logic.
+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{}}
+
+	node3 := &disklayout.ExtentNode{
+		Header: disklayout.ExtentHeader{
+			Magic:      disklayout.ExtentMagic,
+			NumEntries: 1,
+			MaxEntries: 4,
+			Height:     0,
+		},
+		Entries: []disklayout.ExtentEntryPair{
+			{
+				Entry: &disklayout.Extent{
+					FirstFileBlock: 3,
+					Length:         3,
+					StartBlockLo:   6,
+				},
+				Node: nil,
+			},
+		},
+	}
+
+	node2 := &disklayout.ExtentNode{
+		Header: disklayout.ExtentHeader{
+			Magic:      disklayout.ExtentMagic,
+			NumEntries: 1,
+			MaxEntries: 4,
+			Height:     1,
+		},
+		Entries: []disklayout.ExtentEntryPair{
+			{
+				Entry: &disklayout.ExtentIdx{
+					FirstFileBlock: 3,
+					ChildBlockLo:   2,
+				},
+				Node: node3,
+			},
+		},
+	}
+
+	node1 := &disklayout.ExtentNode{
+		Header: disklayout.ExtentHeader{
+			Magic:      disklayout.ExtentMagic,
+			NumEntries: 2,
+			MaxEntries: 4,
+			Height:     0,
+		},
+		Entries: []disklayout.ExtentEntryPair{
+			{
+				Entry: &disklayout.Extent{
+					FirstFileBlock: 0,
+					Length:         1,
+					StartBlockLo:   3,
+				},
+				Node: nil,
+			},
+			{
+				Entry: &disklayout.Extent{
+					FirstFileBlock: 1,
+					Length:         2,
+					StartBlockLo:   4,
+				},
+				Node: nil,
+			},
+		},
+	}
+
+	node0 := &disklayout.ExtentNode{
+		Header: disklayout.ExtentHeader{
+			Magic:      disklayout.ExtentMagic,
+			NumEntries: 2,
+			MaxEntries: 4,
+			Height:     2,
+		},
+		Entries: []disklayout.ExtentEntryPair{
+			{
+				Entry: &disklayout.ExtentIdx{
+					FirstFileBlock: 0,
+					ChildBlockLo:   0,
+				},
+				Node: node1,
+			},
+			{
+				Entry: &disklayout.ExtentIdx{
+					FirstFileBlock: 3,
+					ChildBlockLo:   1,
+				},
+				Node: node2,
+			},
+		},
+	}
+
+	writeTree(mockInode, mockDisk, node0, blkSize)
+
+	r := bytes.NewReader(mockDisk)
+	if err := mockInode.buildExtTree(r, blkSize); err != nil {
+		t.Fatalf("inode.buildExtTree failed: %v", err)
+	}
+
+	if diff := cmp.Diff(&mockInode.root, node0, cmpopts.IgnoreUnexported(disklayout.ExtentNode{})); diff != "" {
+		t.Errorf("extent tree mismatch (-want +got):\n%s", diff)
+	}
+}
+
+// writeTree writes the tree represented by `root` to the inode and disk passed.
+func writeTree(in *inode, disk []byte, root *disklayout.ExtentNode, blkSize uint64) {
+	rootData := binary.Marshal(nil, binary.LittleEndian, root.Header)
+	for _, ep := range root.Entries {
+		rootData = binary.Marshal(rootData, binary.LittleEndian, ep.Entry)
+	}
+
+	copy(in.diskInode.Data(), rootData)
+
+	if root.Header.Height > 0 {
+		for _, ep := range root.Entries {
+			writeTreeToDisk(disk, ep, blkSize)
+		}
+	}
+}
+
+// writeTreeToDisk is the recursive step for writeTree which writes the tree
+// on the disk only.
+func writeTreeToDisk(disk []byte, curNode disklayout.ExtentEntryPair, blkSize uint64) {
+	nodeData := binary.Marshal(nil, binary.LittleEndian, curNode.Node.Header)
+	for _, ep := range curNode.Node.Entries {
+		nodeData = binary.Marshal(nodeData, binary.LittleEndian, ep.Entry)
+	}
+
+	copy(disk[curNode.Entry.PhysicalBlock()*blkSize:], nodeData)
+
+	if curNode.Node.Header.Height > 0 {
+		for _, ep := range curNode.Node.Entries {
+			writeTreeToDisk(disk, ep, blkSize)
+		}
+	}
+}