Use symlink xattr functions from x/sys/unix

Use the symlink xattr syscall wrappers Lgetxattr, Llistxattr and
Lsetxattr from x/sys/unix (introduced in
golang/sys@b90f89a1e7) instead of
providing own wrappers. Leave the functionality of system.Lgetxattr
intact with respect to the retry with a larger buffer, but switch it to
use unix.Lgetxattr.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

libcontainer/system/xattrs_linux.go

@@ -1,54 +1,14 @@
 package system
 
-import (
-	"unsafe"
-
-	"golang.org/x/sys/unix"
-)
-
-var _zero uintptr
-
-// Returns the size of xattrs and nil error
-// Requires path, takes allocated []byte or nil as last argument
-func Llistxattr(path string, dest []byte) (size int, err error) {
-	pathBytes, err := unix.BytePtrFromString(path)
-	if err != nil {
-		return -1, err
-	}
-	var newpathBytes unsafe.Pointer
-	if len(dest) > 0 {
-		newpathBytes = unsafe.Pointer(&dest[0])
-	} else {
-		newpathBytes = unsafe.Pointer(&_zero)
-	}
-
-	_size, _, errno := unix.Syscall6(unix.SYS_LLISTXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(newpathBytes), uintptr(len(dest)), 0, 0, 0)
-	size = int(_size)
-	if errno != 0 {
-		return -1, errno
-	}
-
-	return size, nil
-}
+import "golang.org/x/sys/unix"
 
 // Returns a []byte slice if the xattr is set and nil otherwise
 // Requires path and its attribute as arguments
 func Lgetxattr(path string, attr string) ([]byte, error) {
 	var sz int
-	pathBytes, err := unix.BytePtrFromString(path)
-	if err != nil {
-		return nil, err
-	}
-	attrBytes, err := unix.BytePtrFromString(attr)
-	if err != nil {
-		return nil, err
-	}
-
 	// Start with a 128 length byte array
-	sz = 128
-	dest := make([]byte, sz)
-	destBytes := unsafe.Pointer(&dest[0])
-	_sz, _, errno := unix.Syscall6(unix.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
+	dest := make([]byte, 128)
+	sz, errno := unix.Lgetxattr(path, attr, dest)
 
 	switch {
 	case errno == unix.ENODATA:
@@ -57,44 +17,19 @@ func Lgetxattr(path string, attr string) ([]byte, error) {
 		return nil, errno
 	case errno == unix.ERANGE:
 		// 128 byte array might just not be good enough,
-		// A dummy buffer is used ``uintptr(0)`` to get real size
+		// A dummy buffer is used to get the real size
 		// of the xattrs on disk
-		_sz, _, errno = unix.Syscall6(unix.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(unsafe.Pointer(nil)), uintptr(0), 0, 0)
-		sz = int(_sz)
-		if sz < 0 {
+		sz, errno = unix.Lgetxattr(path, attr, []byte{})
+		if errno != nil {
 			return nil, errno
 		}
 		dest = make([]byte, sz)
-		destBytes := unsafe.Pointer(&dest[0])
-		_sz, _, errno = unix.Syscall6(unix.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
-		if errno != 0 {
+		sz, errno = unix.Lgetxattr(path, attr, dest)
+		if errno != nil {
 			return nil, errno
 		}
-	case errno != 0:
+	case errno != nil:
 		return nil, errno
 	}
-	sz = int(_sz)
 	return dest[:sz], nil
 }
-
-func Lsetxattr(path string, attr string, data []byte, flags int) error {
-	pathBytes, err := unix.BytePtrFromString(path)
-	if err != nil {
-		return err
-	}
-	attrBytes, err := unix.BytePtrFromString(attr)
-	if err != nil {
-		return err
-	}
-	var dataBytes unsafe.Pointer
-	if len(data) > 0 {
-		dataBytes = unsafe.Pointer(&data[0])
-	} else {
-		dataBytes = unsafe.Pointer(&_zero)
-	}
-	_, _, errno := unix.Syscall6(unix.SYS_LSETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(dataBytes), uintptr(len(data)), uintptr(flags), 0)
-	if errno != 0 {
-		return errno
-	}
-	return nil
-}

libcontainer/xattr/xattr_linux.go

@@ -27,12 +27,12 @@ func stringsfromByte(buf []byte) (result []string) {
 }
 
 func Listxattr(path string) ([]string, error) {
-	size, err := system.Llistxattr(path, nil)
+	size, err := unix.Llistxattr(path, nil)
 	if err != nil {
 		return nil, err
 	}
 	buf := make([]byte, size)
-	read, err := system.Llistxattr(path, buf)
+	read, err := unix.Llistxattr(path, buf)
 	if err != nil {
 		return nil, err
 	}
@@ -49,5 +49,5 @@ func Getxattr(path, attr string) (string, error) {
 }
 
 func Setxattr(path, xattr, value string) error {
-	return system.Lsetxattr(path, xattr, []byte(value), 0)
+	return unix.Lsetxattr(path, xattr, []byte(value), 0)
 }