| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 |