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- Notes on the change from 16-bit UIDs to 32-bit UIDs:
- - 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)
- Chris Wing
- wingc@umich.edu
- last updated: January 11, 2000
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