210 lines
6.6 KiB
Go
210 lines
6.6 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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"sync/atomic"
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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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// inode represents an ext inode.
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type inode struct {
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// refs is a reference count. refs is accessed using atomic memory operations.
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refs int64
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// inodeNum is the inode number of this inode on disk. This is used to
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// identify inodes within the ext filesystem.
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inodeNum uint32
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// diskInode gives us access to the inode struct on disk. Immutable.
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diskInode disklayout.Inode
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// root is the root extent node. This lives in the 60 byte diskInode.Blocks().
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// Immutable. Nil if the inode does not use extents.
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root *disklayout.ExtentNode
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}
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// incRef increments the inode ref count.
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func (in *inode) incRef() {
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atomic.AddInt64(&in.refs, 1)
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}
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// tryIncRef tries to increment the ref count. Returns true if successful.
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func (in *inode) tryIncRef() bool {
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for {
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refs := atomic.LoadInt64(&in.refs)
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if refs == 0 {
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return false
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}
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if atomic.CompareAndSwapInt64(&in.refs, refs, refs+1) {
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return true
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}
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}
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}
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// decRef decrements the inode ref count and releases the inode resources if
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// the ref count hits 0.
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//
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// Preconditions: Must have locked fs.mu.
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func (in *inode) decRef(fs *filesystem) {
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if refs := atomic.AddInt64(&in.refs, -1); refs == 0 {
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delete(fs.inodeCache, in.inodeNum)
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} else if refs < 0 {
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panic("ext.inode.decRef() called without holding a reference")
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}
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}
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// newInode is the inode constructor. Reads the inode off disk. Identifies
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// inodes based on the absolute inode number on disk.
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//
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// Preconditions: Must hold the mutex of the filesystem containing dev.
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func newInode(dev io.ReadSeeker, sb disklayout.SuperBlock, bgs []disklayout.BlockGroup, inodeNum uint32) (*inode, error) {
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if inodeNum == 0 {
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panic("inode number 0 on ext filesystems is not possible")
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}
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in := &inode{refs: 1, inodeNum: inodeNum}
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inodeRecordSize := sb.InodeSize()
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if inodeRecordSize == disklayout.OldInodeSize {
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in.diskInode = &disklayout.InodeOld{}
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} else {
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in.diskInode = &disklayout.InodeNew{}
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}
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// Calculate where the inode is actually placed.
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inodesPerGrp := sb.InodesPerGroup()
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blkSize := sb.BlockSize()
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inodeTableOff := bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
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inodeOff := inodeTableOff + uint64(uint32(inodeRecordSize)*getBGOff(inodeNum, inodesPerGrp))
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// Read it from disk and figure out which type of inode this is.
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if err := readFromDisk(dev, int64(inodeOff), in.diskInode); err != nil {
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return nil, err
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}
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if in.diskInode.Flags().Extents {
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in.buildExtTree(dev, blkSize)
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}
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return in, nil
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}
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// getBGNum returns the block group number that a given inode belongs to.
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func getBGNum(inodeNum uint32, inodesPerGrp uint32) uint32 {
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return (inodeNum - 1) / inodesPerGrp
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}
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// getBGOff returns the offset at which the given inode lives in the block
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// group's inode table, i.e. the index of the inode in the inode table.
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func getBGOff(inodeNum uint32, inodesPerGrp uint32) uint32 {
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return (inodeNum - 1) % inodesPerGrp
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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 (in *inode) buildExtTree(dev io.ReadSeeker, blkSize uint64) error {
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rootNodeData := in.diskInode.Data()
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var rootHeader disklayout.ExtentHeader
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binary.Unmarshal(rootNodeData[:disklayout.ExtentStructsSize], binary.LittleEndian, &rootHeader)
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// Root node can not have more than 4 entries: 60 bytes = 1 header + 4 entries.
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if rootHeader.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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rootEntries := make([]disklayout.ExtentEntryPair, rootHeader.NumEntries)
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for i, off := uint16(0), disklayout.ExtentStructsSize; i < rootHeader.NumEntries; i, off = i+1, off+disklayout.ExtentStructsSize {
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var curEntry disklayout.ExtentEntry
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if rootHeader.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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rootEntries[i].Entry = curEntry
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}
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// If this node is internal, perform DFS.
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if rootHeader.Height > 0 {
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for i := uint16(0); i < rootHeader.NumEntries; i++ {
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var err error
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if rootEntries[i].Node, err = buildExtTreeFromDisk(dev, rootEntries[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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in.root = &disklayout.ExtentNode{rootHeader, rootEntries}
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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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if err := readFromDisk(dev, int64(off), &header); 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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if err := readFromDisk(dev, int64(off), curEntry); 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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