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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 |
78 |
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