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package syscallcompat
import (
"os"
"path/filepath"
"sync"
"syscall"
"golang.org/x/sys/unix"
)
var chdirMutex sync.Mutex
// emulateOpenat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateOpenat(dirfd int, path string, flags int, mode uint32) (int, error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
if !filepath.IsAbs(path) {
// Save the old working directory
oldWd, err := os.Getwd()
if err != nil {
return -1, err
}
// Chdir to target directory
err = syscall.Fchdir(dirfd)
if err != nil {
return -1, err
}
// Chdir back at the end
defer os.Chdir(oldWd)
}
return syscall.Open(path, flags, mode)
}
// emulateRenameat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateRenameat(olddirfd int, oldpath string, newdirfd int, newpath string) error {
chdirMutex.Lock()
defer chdirMutex.Unlock()
// Unless both paths are absolute we have to save the old working dir and
// Chdir(oldWd) back to it in the end. If we error out before the first
// chdir, Chdir(oldWd) is unneccassary but does no harm.
if !filepath.IsAbs(oldpath) || !filepath.IsAbs(newpath) {
oldWd, err := os.Getwd()
if err != nil {
return err
}
defer os.Chdir(oldWd)
}
// Make oldpath absolute
oldpath, err := dirfdAbs(olddirfd, oldpath)
if err != nil {
return err
}
// Make newpath absolute
newpath, err = dirfdAbs(newdirfd, newpath)
if err != nil {
return err
}
return syscall.Rename(oldpath, newpath)
}
// emulateUnlinkat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateUnlinkat(dirfd int, path string, flags int) (err error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(cwd)
err = syscall.Fchdir(dirfd)
if err != nil {
return err
}
defer syscall.Fchdir(cwd)
if (flags & unix.AT_REMOVEDIR) != 0 {
return syscall.Rmdir(path)
} else {
return syscall.Unlink(path)
}
}
// emulateMknodat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateMknodat(dirfd int, path string, mode uint32, dev int) error {
chdirMutex.Lock()
defer chdirMutex.Unlock()
if !filepath.IsAbs(path) {
oldWd, err := os.Getwd()
if err != nil {
return err
}
defer os.Chdir(oldWd)
}
path, err := dirfdAbs(dirfd, path)
if err != nil {
return err
}
return syscall.Mknod(path, mode, dev)
}
// dirfdAbs transforms the dirfd-relative "path" to an absolute one. If the
// path is not already absolute, this function will change the working
// directory. The caller has to chdir back.
func dirfdAbs(dirfd int, path string) (string, error) {
if filepath.IsAbs(path) {
return path, nil
}
err := syscall.Fchdir(dirfd)
if err != nil {
return "", err
}
wd, err := os.Getwd()
if err != nil {
return "", err
}
return filepath.Join(wd, path), nil
}
// emulateFchmodat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateFchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(cwd)
err = syscall.Fchdir(dirfd)
if err != nil {
return err
}
defer syscall.Fchdir(cwd)
// We also don't have Lchmod, so emulate it (poorly).
if flags&unix.AT_SYMLINK_NOFOLLOW > 0 {
fi, err := os.Lstat(path)
if err != nil {
return err
}
if fi.Mode()&os.ModeSymlink > 0 {
return nil
}
}
return syscall.Chmod(path, mode)
}
// emulateFchownat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateFchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(cwd)
err = syscall.Fchdir(dirfd)
if err != nil {
return err
}
defer syscall.Fchdir(cwd)
return syscall.Lchown(path, uid, gid)
}
// emulateSymlinkat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateSymlinkat(oldpath string, newdirfd int, newpath string) (err error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(cwd)
err = syscall.Fchdir(newdirfd)
if err != nil {
return err
}
defer syscall.Fchdir(cwd)
return syscall.Symlink(oldpath, newpath)
}
// emulateMkdirat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateMkdirat(dirfd int, path string, mode uint32) (err error) {
chdirMutex.Lock()
defer chdirMutex.Unlock()
cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(cwd)
err = syscall.Fchdir(dirfd)
if err != nil {
return err
}
defer syscall.Fchdir(cwd)
return syscall.Mkdir(path, mode)
}
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