Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.
1 =================================================== 2 Notes on the change from 16-bit UIDs to 32-bit UIDs 3 =================================================== 4 5 :Author: Chris Wing <firstname.lastname@example.org> 6 :Last updated: January 11, 2000 7 8 - kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t 9 when communicating between user and kernel space in an ioctl or data 10 structure. 11 12 - kernel code should use uid_t and gid_t in kernel-private structures and 13 code. 14 15 What's left to be done for 32-bit UIDs on all Linux architectures: 16 17 - Disk quotas have an interesting limitation that is not related to the 18 maximum UID/GID. They are limited by the maximum file size on the 19 underlying filesystem, because quota records are written at offsets 20 corresponding to the UID in question. 21 Further investigation is needed to see if the quota system can cope 22 properly with huge UIDs. If it can deal with 64-bit file offsets on all 23 architectures, this should not be a problem. 24 25 - Decide whether or not to keep backwards compatibility with the system 26 accounting file, or if we should break it as the comments suggest 27 (currently, the old 16-bit UID and GID are still written to disk, and 28 part of the former pad space is used to store separate 32-bit UID and 29 GID) 30 31 - Need to validate that OS emulation calls the 16-bit UID 32 compatibility syscalls, if the OS being emulated used 16-bit UIDs, or 33 uses the 32-bit UID system calls properly otherwise. 34 35 This affects at least: 36 37 - iBCS on Intel 38 39 - sparc32 emulation on sparc64 40 (need to support whatever new 32-bit UID system calls are added to 41 sparc32) 42 43 - Validate that all filesystems behave properly. 44 45 At present, 32-bit UIDs _should_ work for: 46 47 - ext2 48 - ufs 49 - isofs 50 - nfs 51 - coda 52 - udf 53 54 Ioctl() fixups have been made for: 55 56 - ncpfs 57 - smbfs 58 59 Filesystems with simple fixups to prevent 16-bit UID wraparound: 60 61 - minix 62 - sysv 63 - qnx4 64 65 Other filesystems have not been checked yet. 66 67 - The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in 68 all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but 69 more are needed. (as well as new user<->kernel data structures) 70 71 - The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k, 72 sh, and sparc32. Fixing this is probably not that important, but would 73 require adding a new ELF section. 74 75 - The ioctl()s used to control the in-kernel NFS server only support 76 16-bit UIDs on arm, i386, m68k, sh, and sparc32. 77 78 - make sure that the UID mapping feature of AX25 networking works properly 79 (it should be safe because it's always used a 32-bit integer to 80 communicate between user and kernel)