/
walk_unix.go
298 lines (259 loc) · 7.83 KB
/
walk_unix.go
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// SPDX-License-Identifier: BSD-2-Clause
// Some code in this file was derived from https://github.com/karrick/godirwalk.
//go:build unix
package ufs
import (
"bytes"
iofs "io/fs"
"os"
"path"
"path/filepath"
"reflect"
"unsafe"
"golang.org/x/sys/unix"
)
type WalkDiratFunc func(dirfd int, name, relative string, d DirEntry, err error) error
func (fs *UnixFS) WalkDirat(dirfd int, name string, fn WalkDiratFunc) error {
if dirfd == 0 {
// TODO: proper validation, ideally a dedicated function.
dirfd = int(fs.dirfd.Load())
}
info, err := fs.Lstatat(dirfd, name)
if err != nil {
err = fn(dirfd, name, name, nil, err)
} else {
b := newScratchBuffer()
err = fs.walkDir(b, dirfd, name, name, iofs.FileInfoToDirEntry(info), fn)
}
if err == SkipDir || err == SkipAll {
return nil
}
return err
}
func (fs *UnixFS) walkDir(b []byte, parentfd int, name, relative string, d DirEntry, walkDirFn WalkDiratFunc) error {
if err := walkDirFn(parentfd, name, relative, d, nil); err != nil || !d.IsDir() {
if err == SkipDir && d.IsDir() {
// Successfully skipped directory.
err = nil
}
return err
}
dirfd, err := fs.openat(parentfd, name, O_DIRECTORY|O_RDONLY, 0)
if err != nil {
return err
}
defer unix.Close(dirfd)
dirs, err := fs.readDir(dirfd, name, b)
if err != nil {
// Second call, to report ReadDir error.
err = walkDirFn(dirfd, name, relative, d, err)
if err != nil {
if err == SkipDir && d.IsDir() {
err = nil
}
return err
}
}
for _, d1 := range dirs {
// TODO: the path.Join on this line may actually be partially incorrect.
// If we are not walking starting at the root, relative will contain the
// name of the directory we are starting the walk from, which will be
// relative to the root of the filesystem instead of from where the walk
// was initiated from.
//
// ref; https://github.com/blademindeu/panel/issues/5030
if err := fs.walkDir(b, dirfd, d1.Name(), path.Join(relative, d1.Name()), d1, walkDirFn); err != nil {
if err == SkipDir {
break
}
return err
}
}
return nil
}
// ReadDirMap .
// TODO: document
func ReadDirMap[T any](fs *UnixFS, path string, fn func(DirEntry) (T, error)) ([]T, error) {
dirfd, name, closeFd, err := fs.safePath(path)
defer closeFd()
if err != nil {
return nil, err
}
fd, err := fs.openat(dirfd, name, O_DIRECTORY|O_RDONLY, 0)
if err != nil {
return nil, err
}
defer unix.Close(fd)
entries, err := fs.readDir(fd, ".", nil)
if err != nil {
return nil, err
}
out := make([]T, len(entries))
for i, e := range entries {
idx := i
e := e
v, err := fn(e)
if err != nil {
return nil, err
}
out[idx] = v
}
return out, nil
}
// nameOffset is a compile time constant
const nameOffset = int(unsafe.Offsetof(unix.Dirent{}.Name))
func nameFromDirent(de *unix.Dirent) (name []byte) {
// Because this GOOS' syscall.Dirent does not provide a field that specifies
// the name length, this function must first calculate the max possible name
// length, and then search for the NULL byte.
ml := int(de.Reclen) - nameOffset
// Convert syscall.Dirent.Name, which is array of int8, to []byte, by
// overwriting Cap, Len, and Data slice header fields to the max possible
// name length computed above, and finding the terminating NULL byte.
//
// TODO: is there an alternative to the deprecated SliceHeader?
// SliceHeader was mainly deprecated due to it being misused for avoiding
// allocations when converting a byte slice to a string, ref;
// https://go.dev/issue/53003
sh := (*reflect.SliceHeader)(unsafe.Pointer(&name))
sh.Cap = ml
sh.Len = ml
sh.Data = uintptr(unsafe.Pointer(&de.Name[0]))
if index := bytes.IndexByte(name, 0); index >= 0 {
// Found NULL byte; set slice's cap and len accordingly.
sh.Cap = index
sh.Len = index
return
}
// NOTE: This branch is not expected, but included for defensive
// programming, and provides a hard stop on the name based on the structure
// field array size.
sh.Cap = len(de.Name)
sh.Len = sh.Cap
return
}
// modeTypeFromDirent converts a syscall defined constant, which is in purview
// of OS, to a constant defined by Go, assumed by this project to be stable.
//
// When the syscall constant is not recognized, this function falls back to a
// Stat on the file system.
func (fs *UnixFS) modeTypeFromDirent(fd int, de *unix.Dirent, osDirname, osBasename string) (FileMode, error) {
switch de.Type {
case unix.DT_REG:
return 0, nil
case unix.DT_DIR:
return ModeDir, nil
case unix.DT_LNK:
return ModeSymlink, nil
case unix.DT_CHR:
return ModeDevice | ModeCharDevice, nil
case unix.DT_BLK:
return ModeDevice, nil
case unix.DT_FIFO:
return ModeNamedPipe, nil
case unix.DT_SOCK:
return ModeSocket, nil
default:
// If syscall returned unknown type (e.g., DT_UNKNOWN, DT_WHT), then
// resolve actual mode by reading file information.
return fs.modeType(fd, filepath.Join(osDirname, osBasename))
}
}
// modeType returns the mode type of the file system entry identified by
// osPathname by calling os.LStat function, to intentionally not follow symbolic
// links.
//
// Even though os.LStat provides all file mode bits, we want to ensure same
// values returned to caller regardless of whether we obtained file mode bits
// from syscall or stat call. Therefore, mask out the additional file mode bits
// that are provided by stat but not by the syscall, so users can rely on their
// values.
func (fs *UnixFS) modeType(dirfd int, name string) (os.FileMode, error) {
fi, err := fs.Lstatat(dirfd, name)
if err == nil {
return fi.Mode() & ModeType, nil
}
return 0, err
}
var minimumScratchBufferSize = os.Getpagesize()
func newScratchBuffer() []byte {
return make([]byte, minimumScratchBufferSize)
}
func (fs *UnixFS) readDir(fd int, name string, b []byte) ([]DirEntry, error) {
scratchBuffer := b
if scratchBuffer == nil || len(scratchBuffer) < minimumScratchBufferSize {
scratchBuffer = newScratchBuffer()
}
var entries []DirEntry
var workBuffer []byte
var sde unix.Dirent
for {
if len(workBuffer) == 0 {
n, err := unix.Getdents(fd, scratchBuffer)
if err != nil {
if err == unix.EINTR {
continue
}
return nil, convertErrorType(err)
}
if n <= 0 {
// end of directory: normal exit
return entries, nil
}
workBuffer = scratchBuffer[:n] // trim work buffer to number of bytes read
}
// "Go is like C, except that you just put `unsafe` all over the place".
copy((*[unsafe.Sizeof(unix.Dirent{})]byte)(unsafe.Pointer(&sde))[:], workBuffer)
workBuffer = workBuffer[sde.Reclen:] // advance buffer for next iteration through loop
if sde.Ino == 0 {
continue // inode set to 0 indicates an entry that was marked as deleted
}
nameSlice := nameFromDirent(&sde)
nameLength := len(nameSlice)
if nameLength == 0 || (nameSlice[0] == '.' && (nameLength == 1 || (nameLength == 2 && nameSlice[1] == '.'))) {
continue
}
childName := string(nameSlice)
mt, err := fs.modeTypeFromDirent(fd, &sde, name, childName)
if err != nil {
return nil, convertErrorType(err)
}
entries = append(entries, &dirent{name: childName, path: name, modeType: mt, dirfd: fd, fs: fs})
}
}
// dirent stores the name and file system mode type of discovered file system
// entries.
type dirent struct {
name string
path string
modeType FileMode
dirfd int
fs *UnixFS
}
func (de dirent) Name() string {
return de.name
}
func (de dirent) IsDir() bool {
return de.modeType&ModeDir != 0
}
func (de dirent) Type() FileMode {
return de.modeType
}
func (de dirent) Info() (FileInfo, error) {
if de.fs == nil {
return nil, nil
}
return de.fs.Lstatat(de.dirfd, de.name)
}
func (de dirent) Open() (File, error) {
if de.fs == nil {
return nil, nil
}
return de.fs.OpenFileat(de.dirfd, de.name, O_RDONLY, 0)
}
// reset releases memory held by entry err and name, and resets mode type to 0.
func (de *dirent) reset() {
de.name = ""
de.path = ""
de.modeType = 0
}