148 lines
4.7 KiB
Go
148 lines
4.7 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ext
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import (
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"io"
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"gvisor.dev/gvisor/pkg/binary"
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"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
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"gvisor.dev/gvisor/pkg/syserror"
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)
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// extentFile is a type of regular file which uses extents to store file data.
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type extentFile struct {
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regFile regularFile
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// root is the root extent node. This lives in the 60 byte diskInode.Data().
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// Immutable.
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root disklayout.ExtentNode
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}
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// Compiles only if extentFile implements fileReader.
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var _ fileReader = (*extentFile)(nil)
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// Read implements fileReader.getFileReader.
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func (f *extentFile) getFileReader(dev io.ReadSeeker, blkSize uint64, offset uint64) io.Reader {
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panic("unimplemented")
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}
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// newExtentFile is the extent file constructor. It reads the entire extent
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// tree into memory.
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//
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// Preconditions: Must hold the mutex of the filesystem containing dev.
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// TODO(b/134676337): Build extent tree on demand to reduce memory usage.
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func newExtentFile(dev io.ReadSeeker, blkSize uint64, regFile regularFile) (*extentFile, error) {
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file := &extentFile{regFile: regFile}
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file.regFile.impl = file
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err := file.buildExtTree(dev, blkSize)
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if err != nil {
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return nil, err
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}
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return file, nil
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}
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// buildExtTree builds the extent tree by reading it from disk by doing
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// running a simple DFS. It first reads the root node from the inode struct in
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// memory. Then it recursively builds the rest of the tree by reading it off
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// disk.
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//
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// Preconditions:
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// - Must hold the mutex of the filesystem containing dev.
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// - Inode flag InExtents must be set.
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func (f *extentFile) buildExtTree(dev io.ReadSeeker, blkSize uint64) error {
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rootNodeData := f.regFile.inode.diskInode.Data()
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binary.Unmarshal(rootNodeData[:disklayout.ExtentStructsSize], binary.LittleEndian, &f.root.Header)
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// Root node can not have more than 4 entries: 60 bytes = 1 header + 4 entries.
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if f.root.Header.NumEntries > 4 {
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// read(2) specifies that EINVAL should be returned if the file is unsuitable
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// for reading.
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return syserror.EINVAL
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}
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f.root.Entries = make([]disklayout.ExtentEntryPair, f.root.Header.NumEntries)
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for i, off := uint16(0), disklayout.ExtentStructsSize; i < f.root.Header.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
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var curEntry disklayout.ExtentEntry
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if f.root.Header.Height == 0 {
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// Leaf node.
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curEntry = &disklayout.Extent{}
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} else {
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// Internal node.
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curEntry = &disklayout.ExtentIdx{}
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}
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binary.Unmarshal(rootNodeData[off:off+disklayout.ExtentStructsSize], binary.LittleEndian, curEntry)
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f.root.Entries[i].Entry = curEntry
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}
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// If this node is internal, perform DFS.
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if f.root.Header.Height > 0 {
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for i := uint16(0); i < f.root.Header.NumEntries; i++ {
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var err error
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if f.root.Entries[i].Node, err = buildExtTreeFromDisk(dev, f.root.Entries[i].Entry, blkSize); err != nil {
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return err
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}
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}
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}
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return nil
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}
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// buildExtTreeFromDisk reads the extent tree nodes from disk and recursively
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// builds the tree. Performs a simple DFS. It returns the ExtentNode pointed to
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// by the ExtentEntry.
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//
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// Preconditions: Must hold the mutex of the filesystem containing dev.
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func buildExtTreeFromDisk(dev io.ReadSeeker, entry disklayout.ExtentEntry, blkSize uint64) (*disklayout.ExtentNode, error) {
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var header disklayout.ExtentHeader
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off := entry.PhysicalBlock() * blkSize
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err := readFromDisk(dev, int64(off), &header)
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if err != nil {
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return nil, err
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}
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entries := make([]disklayout.ExtentEntryPair, header.NumEntries)
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for i, off := uint16(0), off+disklayout.ExtentStructsSize; i < header.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
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var curEntry disklayout.ExtentEntry
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if header.Height == 0 {
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// Leaf node.
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curEntry = &disklayout.Extent{}
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} else {
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// Internal node.
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curEntry = &disklayout.ExtentIdx{}
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}
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err := readFromDisk(dev, int64(off), curEntry)
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if err != nil {
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return nil, err
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}
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entries[i].Entry = curEntry
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}
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// If this node is internal, perform DFS.
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if header.Height > 0 {
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for i := uint16(0); i < header.NumEntries; i++ {
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var err error
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entries[i].Node, err = buildExtTreeFromDisk(dev, entries[i].Entry, blkSize)
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if err != nil {
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return nil, err
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}
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}
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}
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return &disklayout.ExtentNode{header, entries}, nil
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}
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