syscallcompat: Introduce unlinkat syscall with flags argument

internal/fusefrontend/fs.go

@@ -388,7 +388,7 @@ func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
 	}
 	defer dirfd.Close()
 	// Delete content
-	err = syscallcompat.Unlinkat(int(dirfd.Fd()), cName)
+	err = syscallcompat.Unlinkat(int(dirfd.Fd()), cName, 0)
 	if err != nil {
 		return fuse.ToStatus(err)
 	}

internal/fusefrontend/fs_dir.go

@@ -11,6 +11,8 @@ import (
 	"sync"
 	"syscall"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/hanwen/go-fuse/fuse"
 
 	"github.com/rfjakob/gocryptfs/internal/configfile"
@@ -231,9 +233,7 @@ retry:
 		return fuse.ToStatus(err)
 	}
 	// Actual Rmdir
-	// TODO Use syscall.Unlinkat with the AT_REMOVEDIR flag once it is available
-	// in Go
-	err = syscall.Rmdir(cPath)
+	err = syscallcompat.Unlinkat(int(parentDirFd.Fd()), cName, unix.AT_REMOVEDIR)
 	if err != nil {
 		// This can happen if another file in the directory was created in the
 		// meantime, undo the rename
@@ -245,7 +245,7 @@ retry:
 		return fuse.ToStatus(err)
 	}
 	// Delete "gocryptfs.diriv.rmdir.XYZ"
-	err = syscallcompat.Unlinkat(int(parentDirFd.Fd()), tmpName)
+	err = syscallcompat.Unlinkat(int(parentDirFd.Fd()), tmpName, 0)
 	if err != nil {
 		tlog.Warn.Printf("Rmdir: Could not clean up %s: %v", tmpName, err)
 	}

internal/nametransform/longnames.go

@@ -90,7 +90,7 @@ func ReadLongName(path string) (string, error) {
 
 // DeleteLongName deletes "hashName.name".
 func DeleteLongName(dirfd *os.File, hashName string) error {
-	err := syscallcompat.Unlinkat(int(dirfd.Fd()), hashName+LongNameSuffix)
+	err := syscallcompat.Unlinkat(int(dirfd.Fd()), hashName+LongNameSuffix, 0)
 	if err != nil {
 		tlog.Warn.Printf("DeleteLongName: %v", err)
 	}

internal/syscallcompat/sys_darwin.go

@@ -6,6 +6,8 @@ import (
 	"path/filepath"
 	"sync"
 	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 // Sorry, fallocate is not available on OSX at all and
@@ -71,21 +73,24 @@ func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) error
 }
 
 // Poor man's Unlinkat
-func Unlinkat(dirfd int, path string) error {
+func Unlinkat(dirfd int, path string, flags int) (err 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)
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
 	if err != nil {
 		return err
 	}
-	return syscall.Unlink(path)
+	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)
+	}
 }
 
 // Poor man's Mknodat

internal/syscallcompat/sys_linux.go

@@ -54,9 +54,19 @@ func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err e
 	return syscall.Renameat(olddirfd, oldpath, newdirfd, newpath)
 }
 
-// Unlinkat wraps the Unlinkat syscall.
-func Unlinkat(dirfd int, path string) error {
-	return syscall.Unlinkat(dirfd, path)
+// Unlinkat syscall. In old versions the 'flags' argument was missing, so
+// manually call it by using the corresponding syscall number.
+func Unlinkat(dirfd int, path string, flags int) (err error) {
+	var _p0 *byte
+	_p0, err = syscall.BytePtrFromString(path)
+	if err != nil {
+		return
+	}
+	_, _, e1 := syscall.Syscall(syscall.SYS_UNLINKAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(flags))
+	if e1 != 0 {
+		err = e1
+	}
+	return
 }
 
 // Mknodat wraps the Mknodat syscall.