moby--moby/pkg/system/xattrs_linux.go

package system

import (
	"unsafe"

	"golang.org/x/sys/unix"
)

// Lgetxattr retrieves the value of the extended attribute identified by attr
// and associated with the given path in the file system.
// It will returns a nil slice and nil error if the xattr is not set.
func Lgetxattr(path string, attr string) ([]byte, error) {
	pathBytes, err := unix.BytePtrFromString(path)
	if err != nil {
		return nil, err
	}
	attrBytes, err := unix.BytePtrFromString(attr)
	if err != nil {
		return nil, err
	}

	dest := make([]byte, 128)
	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 == unix.ENODATA {
		return nil, nil
	}
	if errno == unix.ERANGE {
		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 {
		return nil, errno
	}

	return dest[:sz], nil
}

var _zero uintptr

// Lsetxattr sets the value of the extended attribute identified by attr
// and associated with the given path in the file system.
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
}