highuid.txt 2.5 KB

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  1. Notes on the change from 16-bit UIDs to 32-bit UIDs:
  2. - kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t
  3. when communicating between user and kernel space in an ioctl or data
  4. structure.
  5. - kernel code should use uid_t and gid_t in kernel-private structures and
  6. code.
  7. What's left to be done for 32-bit UIDs on all Linux architectures:
  8. - Disk quotas have an interesting limitation that is not related to the
  9. maximum UID/GID. They are limited by the maximum file size on the
  10. underlying filesystem, because quota records are written at offsets
  11. corresponding to the UID in question.
  12. Further investigation is needed to see if the quota system can cope
  13. properly with huge UIDs. If it can deal with 64-bit file offsets on all
  14. architectures, this should not be a problem.
  15. - Decide whether or not to keep backwards compatibility with the system
  16. accounting file, or if we should break it as the comments suggest
  17. (currently, the old 16-bit UID and GID are still written to disk, and
  18. part of the former pad space is used to store separate 32-bit UID and
  19. GID)
  20. - Need to validate that OS emulation calls the 16-bit UID
  21. compatibility syscalls, if the OS being emulated used 16-bit UIDs, or
  22. uses the 32-bit UID system calls properly otherwise.
  23. This affects at least:
  24. SunOS emulation
  25. Solaris emulation
  26. iBCS on Intel
  27. sparc32 emulation on sparc64
  28. (need to support whatever new 32-bit UID system calls are added to
  29. sparc32)
  30. - Validate that all filesystems behave properly.
  31. At present, 32-bit UIDs _should_ work for:
  32. ext2
  33. ufs
  34. isofs
  35. nfs
  36. coda
  37. udf
  38. Ioctl() fixups have been made for:
  39. ncpfs
  40. smbfs
  41. Filesystems with simple fixups to prevent 16-bit UID wraparound:
  42. minix
  43. sysv
  44. qnx4
  45. Other filesystems have not been checked yet.
  46. - The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in
  47. all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but
  48. more are needed. (as well as new user<->kernel data structures)
  49. - The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k,
  50. sh, and sparc32. Fixing this is probably not that important, but would
  51. require adding a new ELF section.
  52. - The ioctl()s used to control the in-kernel NFS server only support
  53. 16-bit UIDs on arm, i386, m68k, sh, and sparc32.
  54. - make sure that the UID mapping feature of AX25 networking works properly
  55. (it should be safe because it's always used a 32-bit integer to
  56. communicate between user and kernel)
  57. Chris Wing
  58. wingc@umich.edu
  59. last updated: January 11, 2000