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