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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package dirwalk
import (
"fmt"
"io/fs"
"os"
"path/filepath"
"sync"
"syscall"
"unsafe"
"go4.org/mem"
"golang.org/x/sys/unix"
)
func init() {
osWalkShallow = linuxWalkShallow
}
var dirEntPool = &sync.Pool{New: func() any { return new(linuxDirEnt) }}
func linuxWalkShallow(dirName mem.RO, fn WalkFunc) error {
const blockSize = 8 << 10
buf := make([]byte, blockSize) // stack-allocated; doesn't escape
nameb := mem.Append(buf[:0], dirName)
nameb = append(nameb, 0)
fd, err := sysOpen(nameb)
if err != nil {
return err
}
defer syscall.Close(fd)
bufp := 0 // starting read position in buf
nbuf := 0 // end valid data in buf
de := dirEntPool.Get().(*linuxDirEnt)
defer de.cleanAndPutInPool()
de.root = dirName
for {
if bufp >= nbuf {
bufp = 0
nbuf, err = readDirent(fd, buf)
if err != nil {
return err
}
if nbuf <= 0 {
return nil
}
}
consumed, name := parseDirEnt(&de.d, buf[bufp:nbuf])
bufp += consumed
if len(name) == 0 || string(name) == "." || string(name) == ".." {
continue
}
de.name = mem.B(name)
if err := fn(de.name, de); err != nil {
return err
}
}
}
type linuxDirEnt struct {
root mem.RO
d syscall.Dirent
name mem.RO
}
func (de *linuxDirEnt) cleanAndPutInPool() {
de.root = mem.RO{}
de.name = mem.RO{}
dirEntPool.Put(de)
}
func (de *linuxDirEnt) Name() string { return de.name.StringCopy() }
func (de *linuxDirEnt) Info() (fs.FileInfo, error) {
return os.Lstat(filepath.Join(de.root.StringCopy(), de.name.StringCopy()))
}
func (de *linuxDirEnt) IsDir() bool {
return de.d.Type == syscall.DT_DIR
}
func (de *linuxDirEnt) Type() fs.FileMode {
switch de.d.Type {
case syscall.DT_BLK:
return fs.ModeDevice // shrug
case syscall.DT_CHR:
return fs.ModeCharDevice
case syscall.DT_DIR:
return fs.ModeDir
case syscall.DT_FIFO:
return fs.ModeNamedPipe
case syscall.DT_LNK:
return fs.ModeSymlink
case syscall.DT_REG:
return 0
case syscall.DT_SOCK:
return fs.ModeSocket
default:
return fs.ModeIrregular // shrug
}
}
func direntNamlen(dirent *syscall.Dirent) int {
const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name))
limit := dirent.Reclen - fixedHdr
const dirNameLen = 256 // sizeof syscall.Dirent.Name
if limit > dirNameLen {
limit = dirNameLen
}
for i := uint16(0); i < limit; i++ {
if dirent.Name[i] == 0 {
return int(i)
}
}
panic("failed to find terminating 0 byte in dirent")
}
func parseDirEnt(dirent *syscall.Dirent, buf []byte) (consumed int, name []byte) {
// golang.org/issue/37269
copy(unsafe.Slice((*byte)(unsafe.Pointer(dirent)), unsafe.Sizeof(syscall.Dirent{})), buf)
if v := unsafe.Offsetof(dirent.Reclen) + unsafe.Sizeof(dirent.Reclen); uintptr(len(buf)) < v {
panic(fmt.Sprintf("buf size of %d smaller than dirent header size %d", len(buf), v))
}
if len(buf) < int(dirent.Reclen) {
panic(fmt.Sprintf("buf size %d < record length %d", len(buf), dirent.Reclen))
}
consumed = int(dirent.Reclen)
if dirent.Ino == 0 { // File absent in directory.
return
}
name = unsafe.Slice((*byte)(unsafe.Pointer(&dirent.Name[0])), direntNamlen(dirent))
return
}
func sysOpen(name []byte) (fd int, err error) {
if len(name) == 0 || name[len(name)-1] != 0 {
return 0, syscall.EINVAL
}
var dirfd int = unix.AT_FDCWD
for {
r0, _, e1 := syscall.Syscall(unix.SYS_OPENAT, uintptr(dirfd),
uintptr(unsafe.Pointer(&name[0])), 0)
if e1 == 0 {
return int(r0), nil
}
if e1 == syscall.EINTR {
// Since https://golang.org/doc/go1.14#runtime we
// need to loop on EINTR on more places.
continue
}
return 0, syscall.Errno(e1)
}
}
func readDirent(fd int, buf []byte) (n int, err error) {
for {
nbuf, err := syscall.ReadDirent(fd, buf)
if err != syscall.EINTR {
return nbuf, err
}
}
}
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