//go:build linux

/*

Copyright The containerd 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 fs

import (

"fmt"

"os"

"syscall"

"unsafe"

)

func locateDummyIfEmpty(path string) (string, error) {

children, err := os.ReadDir(path)

if err != nil {

return "", err

}

if len(children) != 0 {

return "", nil

}

dummyFile, err := os.CreateTemp(path, "fsutils-dummy")

if err != nil {

return "", err

}

name := dummyFile.Name()

err = dummyFile.Close()

return name, err

}

// SupportsDType returns whether the filesystem mounted on path supports d_type

func SupportsDType(path string) (bool, error) {

// locate dummy so that we have at least one dirent

dummy, err := locateDummyIfEmpty(path)

if err != nil {

return false, err

}

if dummy != "" {

defer os.Remove(dummy)

}

visited := 0

supportsDType := true

fn := func(ent *syscall.Dirent) bool {

visited++

if ent.Type == syscall.DT_UNKNOWN {

supportsDType = false

// stop iteration

return true

}

// continue iteration

return false

}

if err = iterateReadDir(path, fn); err != nil {

return false, err

}

if visited == 0 {

return false, fmt.Errorf("did not hit any dirent during iteration %s", path)

}

return supportsDType, nil

}

func iterateReadDir(path string, fn func(*syscall.Dirent) bool) error {

d, err := os.Open(path)

if err != nil {

return err

}

defer d.Close()

fd := int(d.Fd())

buf := make([]byte, 4096)

for {

nbytes, err := syscall.ReadDirent(fd, buf)

if err != nil {

return err

}

if nbytes == 0 {

break

}

for off := 0; off < nbytes; {

ent := (*syscall.Dirent)(unsafe.Pointer(&buf[off]))

if stop := fn(ent); stop {

return nil

}

off += int(ent.Reclen)

}

}

return nil

}