104 lines
2.2 KiB
Go
104 lines
2.2 KiB
Go
// +build linux
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/*
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Copyright The containerd Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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package fs
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import (
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"fmt"
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"io/ioutil"
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"os"
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"syscall"
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"unsafe"
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)
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func locateDummyIfEmpty(path string) (string, error) {
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children, err := ioutil.ReadDir(path)
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if err != nil {
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return "", err
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}
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if len(children) != 0 {
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return "", nil
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}
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dummyFile, err := ioutil.TempFile(path, "fsutils-dummy")
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if err != nil {
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return "", err
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}
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name := dummyFile.Name()
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err = dummyFile.Close()
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return name, err
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}
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// SupportsDType returns whether the filesystem mounted on path supports d_type
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func SupportsDType(path string) (bool, error) {
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// locate dummy so that we have at least one dirent
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dummy, err := locateDummyIfEmpty(path)
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if err != nil {
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return false, err
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}
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if dummy != "" {
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defer os.Remove(dummy)
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}
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visited := 0
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supportsDType := true
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fn := func(ent *syscall.Dirent) bool {
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visited++
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if ent.Type == syscall.DT_UNKNOWN {
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supportsDType = false
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// stop iteration
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return true
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}
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// continue iteration
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return false
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}
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if err = iterateReadDir(path, fn); err != nil {
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return false, err
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}
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if visited == 0 {
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return false, fmt.Errorf("did not hit any dirent during iteration %s", path)
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}
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return supportsDType, nil
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}
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func iterateReadDir(path string, fn func(*syscall.Dirent) bool) error {
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d, err := os.Open(path)
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if err != nil {
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return err
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}
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defer d.Close()
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fd := int(d.Fd())
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buf := make([]byte, 4096)
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for {
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nbytes, err := syscall.ReadDirent(fd, buf)
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if err != nil {
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return err
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}
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if nbytes == 0 {
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break
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}
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for off := 0; off < nbytes; {
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ent := (*syscall.Dirent)(unsafe.Pointer(&buf[off]))
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if stop := fn(ent); stop {
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return nil
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}
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off += int(ent.Reclen)
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}
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}
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return nil
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}
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