LXR linux/Documentation/highuid.txt

   1Notes on the change from 16-bit UIDs to 32-bit UIDs:
   2
   3- kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t
   4  when communicating between user and kernel space in an ioctl or data
   5  structure.
   6
   7- kernel code should use uid_t and gid_t in kernel-private structures and
   8  code.
   9
  10What's left to be done for 32-bit UIDs on all Linux architectures:
  11
  12- Disk quotas have an interesting limitation that is not related to the
  13  maximum UID/GID. They are limited by the maximum file size on the
  14  underlying filesystem, because quota records are written at offsets
  15  corresponding to the UID in question.
  16  Further investigation is needed to see if the quota system can cope
  17  properly with huge UIDs. If it can deal with 64-bit file offsets on all 
  18  architectures, this should not be a problem.
  19
  20- Decide whether or not to keep backwards compatibility with the system
  21  accounting file, or if we should break it as the comments suggest
  22  (currently, the old 16-bit UID and GID are still written to disk, and
  23  part of the former pad space is used to store separate 32-bit UID and
  24  GID)
  25
  26- Need to validate that OS emulation calls the 16-bit UID
  27  compatibility syscalls, if the OS being emulated used 16-bit UIDs, or
  28  uses the 32-bit UID system calls properly otherwise.
  29
  30  This affects at least:
  31        iBCS on Intel
  32
  33        sparc32 emulation on sparc64
  34        (need to support whatever new 32-bit UID system calls are added to
  35        sparc32)
  36
  37- Validate that all filesystems behave properly.
  38
  39  At present, 32-bit UIDs _should_ work for:
  40        ext2
  41        ufs
  42        isofs
  43        nfs
  44        coda
  45        udf
  46
  47  Ioctl() fixups have been made for:
  48        ncpfs
  49        smbfs
  50
  51  Filesystems with simple fixups to prevent 16-bit UID wraparound:
  52        minix
  53        sysv
  54        qnx4
  55
  56  Other filesystems have not been checked yet.
  57
  58- The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in
  59  all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but
  60  more are needed. (as well as new user<->kernel data structures)
  61
  62- The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k,
  63  sh, and sparc32. Fixing this is probably not that important, but would
  64  require adding a new ELF section.
  65
  66- The ioctl()s used to control the in-kernel NFS server only support
  67  16-bit UIDs on arm, i386, m68k, sh, and sparc32.
  68
  69- make sure that the UID mapping feature of AX25 networking works properly
  70  (it should be safe because it's always used a 32-bit integer to
  71  communicate between user and kernel)
  72
  73
  74Chris Wing
  75wingc@umich.edu
  76
  77last updated: January 11, 2000
  78