217 lines
6.7 KiB
Go
217 lines
6.7 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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"fmt"
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"sync/atomic"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/fsimpl/ext/disklayout"
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"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
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"gvisor.dev/gvisor/pkg/sentry/vfs"
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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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//
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// inode uses the same inheritance pattern that pkg/sentry/vfs structures use.
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// This has been done to increase memory locality.
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//
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// Implementations:
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// inode --
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// |-- dir
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// |-- symlink
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// |-- regular--
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// |-- extent file
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// |-- block map file
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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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// fs is the containing filesystem.
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fs *filesystem
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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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// blkSize is the fs data block size. Same as filesystem.sb.BlockSize().
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blkSize uint64
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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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// This is immutable. The first field of the implementations must have inode
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// as the first field to ensure temporality.
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impl interface{}
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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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// Precondition: Must have locked filesystem.mu.
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func (in *inode) decRef() {
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if refs := atomic.AddInt64(&in.refs, -1); refs == 0 {
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delete(in.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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func newInode(fs *filesystem, 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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inodeRecordSize := fs.sb.InodeSize()
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var diskInode disklayout.Inode
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if inodeRecordSize == disklayout.OldInodeSize {
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diskInode = &disklayout.InodeOld{}
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} else {
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diskInode = &disklayout.InodeNew{}
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}
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// Calculate where the inode is actually placed.
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inodesPerGrp := fs.sb.InodesPerGroup()
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blkSize := fs.sb.BlockSize()
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inodeTableOff := fs.bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
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inodeOff := inodeTableOff + uint64(uint32(inodeRecordSize)*getBGOff(inodeNum, inodesPerGrp))
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if err := readFromDisk(fs.dev, int64(inodeOff), diskInode); err != nil {
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return nil, err
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}
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// Build the inode based on its type.
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inode := inode{
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fs: fs,
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inodeNum: inodeNum,
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blkSize: blkSize,
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diskInode: diskInode,
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}
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switch diskInode.Mode().FileType() {
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case linux.ModeSymlink:
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f, err := newSymlink(inode)
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if err != nil {
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return nil, err
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}
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return &f.inode, nil
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case linux.ModeRegular:
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f, err := newRegularFile(inode)
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if err != nil {
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return nil, err
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}
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return &f.inode, nil
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case linux.ModeDirectory:
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f, err := newDirectroy(inode, fs.sb.IncompatibleFeatures().DirentFileType)
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if err != nil {
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return nil, err
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}
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return &f.inode, nil
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default:
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// TODO(b/134676337): Return appropriate errors for sockets, pipes and devices.
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return nil, syserror.EINVAL
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}
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}
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// open creates and returns a file description for the dentry passed in.
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func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
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ats := vfs.AccessTypesForOpenFlags(flags)
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if err := in.checkPermissions(rp.Credentials(), ats); err != nil {
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return nil, err
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}
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mnt := rp.Mount()
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switch in.impl.(type) {
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case *regularFile:
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var fd regularFileFD
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fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
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return &fd.vfsfd, nil
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case *directory:
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// Can't open directories writably. This check is not necessary for a read
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// only filesystem but will be required when write is implemented.
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if ats&vfs.MayWrite != 0 {
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return nil, syserror.EISDIR
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}
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var fd directoryFD
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fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
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return &fd.vfsfd, nil
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case *symlink:
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if flags&linux.O_PATH == 0 {
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// Can't open symlinks without O_PATH.
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return nil, syserror.ELOOP
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}
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var fd symlinkFD
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fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
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return &fd.vfsfd, nil
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default:
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panic(fmt.Sprintf("unknown inode type: %T", in.impl))
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}
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}
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func (in *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
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return vfs.GenericCheckPermissions(creds, ats, in.isDir(), uint16(in.diskInode.Mode()), in.diskInode.UID(), in.diskInode.GID())
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}
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// statTo writes the statx fields to the output parameter.
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func (in *inode) statTo(stat *linux.Statx) {
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stat.Mask = linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK |
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linux.STATX_UID | linux.STATX_GID | linux.STATX_INO | linux.STATX_SIZE |
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linux.STATX_ATIME | linux.STATX_CTIME | linux.STATX_MTIME
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stat.Blksize = uint32(in.blkSize)
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stat.Mode = uint16(in.diskInode.Mode())
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stat.Nlink = uint32(in.diskInode.LinksCount())
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stat.UID = uint32(in.diskInode.UID())
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stat.GID = uint32(in.diskInode.GID())
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stat.Ino = uint64(in.inodeNum)
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stat.Size = in.diskInode.Size()
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stat.Atime = in.diskInode.AccessTime().StatxTimestamp()
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stat.Ctime = in.diskInode.ChangeTime().StatxTimestamp()
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stat.Mtime = in.diskInode.ModificationTime().StatxTimestamp()
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// TODO(b/134676337): Set stat.Blocks which is the number of 512 byte blocks
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// (including metadata blocks) required to represent this file.
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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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