| =================================================== |
| Notes on the change from 16-bit UIDs to 32-bit UIDs |
| =================================================== |
| |
| :Author: Chris Wing <wingc@umich.edu> |
| :Last updated: January 11, 2000 |
| |
| - kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t |
| when communicating between user and kernel space in an ioctl or data |
| structure. |
| |
| - kernel code should use uid_t and gid_t in kernel-private structures and |
| code. |
| |
| What's left to be done for 32-bit UIDs on all Linux architectures: |
| |
| - Disk quotas have an interesting limitation that is not related to the |
| maximum UID/GID. They are limited by the maximum file size on the |
| underlying filesystem, because quota records are written at offsets |
| corresponding to the UID in question. |
| Further investigation is needed to see if the quota system can cope |
| properly with huge UIDs. If it can deal with 64-bit file offsets on all |
| architectures, this should not be a problem. |
| |
| - Decide whether or not to keep backwards compatibility with the system |
| accounting file, or if we should break it as the comments suggest |
| (currently, the old 16-bit UID and GID are still written to disk, and |
| part of the former pad space is used to store separate 32-bit UID and |
| GID) |
| |
| - Need to validate that OS emulation calls the 16-bit UID |
| compatibility syscalls, if the OS being emulated used 16-bit UIDs, or |
| uses the 32-bit UID system calls properly otherwise. |
| |
| This affects at least: |
| |
| - iBCS on Intel |
| |
| - sparc32 emulation on sparc64 |
| (need to support whatever new 32-bit UID system calls are added to |
| sparc32) |
| |
| - Validate that all filesystems behave properly. |
| |
| At present, 32-bit UIDs _should_ work for: |
| |
| - ext2 |
| - ufs |
| - isofs |
| - nfs |
| - coda |
| - udf |
| |
| Ioctl() fixups have been made for: |
| |
| - ncpfs |
| - smbfs |
| |
| Filesystems with simple fixups to prevent 16-bit UID wraparound: |
| |
| - minix |
| - sysv |
| - qnx4 |
| |
| Other filesystems have not been checked yet. |
| |
| - The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in |
| all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but |
| more are needed. (as well as new user<->kernel data structures) |
| |
| - The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k, |
| sh, and sparc32. Fixing this is probably not that important, but would |
| require adding a new ELF section. |
| |
| - The ioctl()s used to control the in-kernel NFS server only support |
| 16-bit UIDs on arm, i386, m68k, sh, and sparc32. |
| |
| - make sure that the UID mapping feature of AX25 networking works properly |
| (it should be safe because it's always used a 32-bit integer to |
| communicate between user and kernel) |
