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Linux/Documentation/highuid.txt

  1 Notes 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 
 10 What'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 
 74 Chris Wing
 75 wingc@umich.edu
 76 
 77 last updated: January 11, 2000

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