0001 ===================================================
0002 Notes on the change from 16-bit UIDs to 32-bit UIDs
0003 ===================================================
0004
0005 :Author: Chris Wing <wingc@umich.edu>
0006 :Last updated: January 11, 2000
0007
0008 - kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t
0009 when communicating between user and kernel space in an ioctl or data
0010 structure.
0011
0012 - kernel code should use uid_t and gid_t in kernel-private structures and
0013 code.
0014
0015 What's left to be done for 32-bit UIDs on all Linux architectures:
0016
0017 - Disk quotas have an interesting limitation that is not related to the
0018 maximum UID/GID. They are limited by the maximum file size on the
0019 underlying filesystem, because quota records are written at offsets
0020 corresponding to the UID in question.
0021 Further investigation is needed to see if the quota system can cope
0022 properly with huge UIDs. If it can deal with 64-bit file offsets on all
0023 architectures, this should not be a problem.
0024
0025 - Decide whether or not to keep backwards compatibility with the system
0026 accounting file, or if we should break it as the comments suggest
0027 (currently, the old 16-bit UID and GID are still written to disk, and
0028 part of the former pad space is used to store separate 32-bit UID and
0029 GID)
0030
0031 - Need to validate that OS emulation calls the 16-bit UID
0032 compatibility syscalls, if the OS being emulated used 16-bit UIDs, or
0033 uses the 32-bit UID system calls properly otherwise.
0034
0035 This affects at least:
0036
0037 - iBCS on Intel
0038
0039 - sparc32 emulation on sparc64
0040 (need to support whatever new 32-bit UID system calls are added to
0041 sparc32)
0042
0043 - Validate that all filesystems behave properly.
0044
0045 At present, 32-bit UIDs _should_ work for:
0046
0047 - ext2
0048 - ufs
0049 - isofs
0050 - nfs
0051 - coda
0052 - udf
0053
0054 Ioctl() fixups have been made for:
0055
0056 - ncpfs
0057 - smbfs
0058
0059 Filesystems with simple fixups to prevent 16-bit UID wraparound:
0060
0061 - minix
0062 - sysv
0063 - qnx4
0064
0065 Other filesystems have not been checked yet.
0066
0067 - The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in
0068 all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but
0069 more are needed. (as well as new user<->kernel data structures)
0070
0071 - The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k,
0072 sh, and sparc32. Fixing this is probably not that important, but would
0073 require adding a new ELF section.
0074
0075 - The ioctl()s used to control the in-kernel NFS server only support
0076 16-bit UIDs on arm, i386, m68k, sh, and sparc32.
0077
0078 - make sure that the UID mapping feature of AX25 networking works properly
0079 (it should be safe because it's always used a 32-bit integer to
0080 communicate between user and kernel)
