| =================================================== | |
| 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) |