[U]

[..]
  1. UIO_READ
  2. UIO_SYSSPACE
  3. UIO_USERISPACE
  4. UIO_USERSPACE
  5. UIO_WRITE
  6. UNIMP
  7. UNINIT_ARRAY_ELEMS
  8. UNINIT_PAGES
  9. UNLOCKME
  10. USERSPACETOP
  11. USERSTACK
  12. USE_LONGLONG
  13. USING_ERR_CODES
[..]