1===================================================
2Notes on the change from 16-bit UIDs to 32-bit UIDs
3===================================================
4
5:Author: Chris Wing <wingc@umich.edu>
6:Last updated: January 11, 2000
7
8- kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t
9  when communicating between user and kernel space in an ioctl or data
10  structure.
11
12- kernel code should use uid_t and gid_t in kernel-private structures and
13  code.
14
15What's left to be done for 32-bit UIDs on all Linux architectures:
16
17- Disk quotas have an interesting limitation that is not related to the
18  maximum UID/GID. They are limited by the maximum file size on the
19  underlying filesystem, because quota records are written at offsets
20  corresponding to the UID in question.
21  Further investigation is needed to see if the quota system can cope
22  properly with huge UIDs. If it can deal with 64-bit file offsets on all
23  architectures, this should not be a problem.
24
25- Decide whether or not to keep backwards compatibility with the system
26  accounting file, or if we should break it as the comments suggest
27  (currently, the old 16-bit UID and GID are still written to disk, and
28  part of the former pad space is used to store separate 32-bit UID and
29  GID)
30
31- Need to validate that OS emulation calls the 16-bit UID
32  compatibility syscalls, if the OS being emulated used 16-bit UIDs, or
33  uses the 32-bit UID system calls properly otherwise.
34
35  This affects at least:
36
37	- iBCS on Intel
38
39	- sparc32 emulation on sparc64
40	  (need to support whatever new 32-bit UID system calls are added to
41	  sparc32)
42
43- Validate that all filesystems behave properly.
44
45  At present, 32-bit UIDs _should_ work for:
46
47	- ext2
48	- ufs
49	- isofs
50	- nfs
51	- coda
52	- udf
53
54  Ioctl() fixups have been made for:
55
56	- ncpfs
57	- smbfs
58
59  Filesystems with simple fixups to prevent 16-bit UID wraparound:
60
61	- minix
62	- sysv
63	- qnx4
64
65  Other filesystems have not been checked yet.
66
67- The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in
68  all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but
69  more are needed. (as well as new user<->kernel data structures)
70
71- The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k,
72  sh, and sparc32. Fixing this is probably not that important, but would
73  require adding a new ELF section.
74
75- The ioctl()s used to control the in-kernel NFS server only support
76  16-bit UIDs on arm, i386, m68k, sh, and sparc32.
77
78- make sure that the UID mapping feature of AX25 networking works properly
79  (it should be safe because it's always used a 32-bit integer to
80  communicate between user and kernel)
81