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// 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 (
"fmt"
"io"
"sync/atomic"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"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 --
// |-- dir
// |-- symlink
// |-- regular--
// |-- extent file
// |-- block map file
type inode struct {
// refs is a reference count. refs is accessed using atomic memory operations.
refs int64
// inodeNum is the inode number of this inode on disk. This is used to
// identify inodes within the ext filesystem.
inodeNum uint32
// dev represents the underlying device. Same as filesystem.dev.
dev io.ReaderAt
// blkSize is the fs data block size. Same as filesystem.sb.BlockSize().
blkSize uint64
// diskInode gives us access to the inode struct on disk. Immutable.
diskInode disklayout.Inode
// 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.
func (in *inode) incRef() {
atomic.AddInt64(&in.refs, 1)
}
// tryIncRef tries to increment the ref count. Returns true if successful.
func (in *inode) tryIncRef() bool {
for {
refs := atomic.LoadInt64(&in.refs)
if refs == 0 {
return false
}
if atomic.CompareAndSwapInt64(&in.refs, refs, refs+1) {
return true
}
}
}
// decRef decrements the inode ref count and releases the inode resources if
// the ref count hits 0.
//
// Precondition: Must have locked fs.mu.
func (in *inode) decRef(fs *filesystem) {
if refs := atomic.AddInt64(&in.refs, -1); refs == 0 {
delete(fs.inodeCache, in.inodeNum)
} else if refs < 0 {
panic("ext.inode.decRef() called without holding a reference")
}
}
// newInode is the inode constructor. Reads the inode off disk. Identifies
// inodes based on the absolute inode number on disk.
func newInode(fs *filesystem, inodeNum uint32) (*inode, error) {
if inodeNum == 0 {
panic("inode number 0 on ext filesystems is not possible")
}
inodeRecordSize := fs.sb.InodeSize()
var diskInode disklayout.Inode
if inodeRecordSize == disklayout.OldInodeSize {
diskInode = &disklayout.InodeOld{}
} else {
diskInode = &disklayout.InodeNew{}
}
// Calculate where the inode is actually placed.
inodesPerGrp := fs.sb.InodesPerGroup()
blkSize := fs.sb.BlockSize()
inodeTableOff := fs.bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
inodeOff := inodeTableOff + uint64(uint32(inodeRecordSize)*getBGOff(inodeNum, inodesPerGrp))
if err := readFromDisk(fs.dev, int64(inodeOff), diskInode); err != nil {
return nil, err
}
// Build the inode based on its type.
inode := inode{
inodeNum: inodeNum,
dev: fs.dev,
blkSize: blkSize,
diskInode: diskInode,
}
switch diskInode.Mode().FileType() {
case linux.ModeSymlink:
f, err := newSymlink(inode)
if err != nil {
return nil, err
}
return &f.inode, nil
case linux.ModeRegular:
f, err := newRegularFile(inode)
if err != nil {
return nil, err
}
return &f.inode, nil
case linux.ModeDirectory:
f, err := newDirectroy(inode, fs.sb.IncompatibleFeatures().DirentFileType)
if err != nil {
return nil, err
}
return &f.inode, nil
default:
// TODO(b/134676337): Return appropriate errors for sockets, pipes and devices.
return nil, syserror.EINVAL
}
}
// open creates and returns a file description for the dentry passed in.
func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
ats := vfs.AccessTypesForOpenFlags(flags)
if err := in.checkPermissions(rp.Credentials(), ats); err != nil {
return nil, err
}
switch in.impl.(type) {
case *regularFile:
var fd regularFileFD
fd.flags = flags
fd.vfsfd.Init(&fd, rp.Mount(), vfsd)
return &fd.vfsfd, nil
case *directory:
// Can't open directories writably. This check is not necessary for a read
// only filesystem but will be required when write is implemented.
if ats&vfs.MayWrite != 0 {
return nil, syserror.EISDIR
}
var fd directoryFD
fd.vfsfd.Init(&fd, rp.Mount(), vfsd)
fd.flags = flags
return &fd.vfsfd, nil
case *symlink:
if flags&linux.O_PATH == 0 {
// Can't open symlinks without O_PATH.
return nil, syserror.ELOOP
}
var fd symlinkFD
fd.flags = flags
fd.vfsfd.Init(&fd, rp.Mount(), vfsd)
return &fd.vfsfd, nil
default:
panic(fmt.Sprintf("unknown inode type: %T", in.impl))
}
}
func (in *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
return vfs.GenericCheckPermissions(creds, ats, in.isDir(), uint16(in.diskInode.Mode()), in.diskInode.UID(), in.diskInode.GID())
}
// statTo writes the statx fields to the output parameter.
func (in *inode) statTo(stat *linux.Statx) {
stat.Mask = linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK |
linux.STATX_UID | linux.STATX_GID | linux.STATX_INO | linux.STATX_SIZE |
linux.STATX_ATIME | linux.STATX_CTIME | linux.STATX_MTIME
stat.Blksize = uint32(in.blkSize)
stat.Mode = uint16(in.diskInode.Mode())
stat.Nlink = uint32(in.diskInode.LinksCount())
stat.UID = uint32(in.diskInode.UID())
stat.GID = uint32(in.diskInode.GID())
stat.Ino = uint64(in.inodeNum)
stat.Size = in.diskInode.Size()
stat.Atime = in.diskInode.AccessTime().StatxTimestamp()
stat.Ctime = in.diskInode.ChangeTime().StatxTimestamp()
stat.Mtime = in.diskInode.ModificationTime().StatxTimestamp()
// TODO(b/134676337): Set stat.Blocks which is the number of 512 byte blocks
// (including metadata blocks) required to represent this file.
}
// getBGNum returns the block group number that a given inode belongs to.
func getBGNum(inodeNum uint32, inodesPerGrp uint32) uint32 {
return (inodeNum - 1) / inodesPerGrp
}
// getBGOff returns the offset at which the given inode lives in the block
// group's inode table, i.e. the index of the inode in the inode table.
func getBGOff(inodeNum uint32, inodesPerGrp uint32) uint32 {
return (inodeNum - 1) % inodesPerGrp
}
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