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