Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/Documentation/highuid.txt
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
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Tag kernel26-2.6.12-alx-r9
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 | SunOS emulation |
32 | Solaris emulation |
33 | iBCS on Intel |
34 | |
35 | sparc32 emulation on sparc64 |
36 | (need to support whatever new 32-bit UID system calls are added to |
37 | sparc32) |
38 | |
39 | - Validate that all filesystems behave properly. |
40 | |
41 | At present, 32-bit UIDs _should_ work for: |
42 | ext2 |
43 | ufs |
44 | isofs |
45 | nfs |
46 | coda |
47 | udf |
48 | |
49 | Ioctl() fixups have been made for: |
50 | ncpfs |
51 | smbfs |
52 | |
53 | Filesystems with simple fixups to prevent 16-bit UID wraparound: |
54 | minix |
55 | sysv |
56 | qnx4 |
57 | |
58 | Other filesystems have not been checked yet. |
59 | |
60 | - The ncpfs and smpfs filesystems can not presently use 32-bit UIDs in |
61 | all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but |
62 | more are needed. (as well as new user<->kernel data structures) |
63 | |
64 | - The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k, |
65 | sh, and sparc32. Fixing this is probably not that important, but would |
66 | require adding a new ELF section. |
67 | |
68 | - The ioctl()s used to control the in-kernel NFS server only support |
69 | 16-bit UIDs on arm, i386, m68k, sh, and sparc32. |
70 | |
71 | - make sure that the UID mapping feature of AX25 networking works properly |
72 | (it should be safe because it's always used a 32-bit integer to |
73 | communicate between user and kernel) |
74 | |
75 | |
76 | Chris Wing |
77 | wingc@umich.edu |
78 | |
79 | last updated: January 11, 2000 |