Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
flat view
From: Yann Droneaud <hidden>
Date: 2018-05-17 16:43:34
Also in:
linux-arch, lkml
Hi, Le mercredi 16 mai 2018 à 15:20 +0100, Dave Martin a écrit :
There are constraints on defining AT_* auxvec tags that are not obvious to the casual maintainer of either the global <uapi/linux/auxvec.h> or the arch-specific headers. This is likely to lead to mistakes. (I certainly fell foul of it...) For the benefit of future maintainers, this patch collects the relevant information in one place, documenting how the namespace needs to be managed, and noting all the values currently in use. Maintaining a global list may result in some merge conflicts, but AT_* values are not added frequently. I'm open to suggestions on the best approach. I also assume that values 38 and 39 may have been used for historical purposes, such as an architecture that is no longer supported. If they have definitely never been used for anything, they could be removed from the "reserved" list.
Some of those AT_* values are described in getauxval(3) man-page: http://man7.org/linux/man-pages/man3/getauxval.3.html https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man3/g etauxval.3?id=4eae8eb731386d81797d5c30365426722410874e And glibc provides <elf.h> with definitions for almost all AT_*, regardless of the current target architecture: https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/elf.h;h=954f3266f7 11ab83996670ea504a17dcf668e061;hb=23158b08a0908f381459f273a984c6fd32836 3cb#l1135 Also, despite not being listed as a reserved namespace by POSIX, one should try to avoid name collision with other AT_ constants, those used with *at() functions (openat(), etc.): - AT_EACCESS - AT_EMPTY_PATH - AT_FDCWD - AT_NO_AUTOMOUNT - AT_REMOVEDIR - AT_STATX_DONT_SYNC - AT_STATX_FORCE_SYNC - AT_STATX_SYNC_AS_STAT - AT_SYMLINK_FOLLOW - AT_SYMLINK_NOFOLLOW http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fcntl.h.html http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.htm l#tag_15_02_02 https://sourceware.org/git/?p=glibc.git;a=blob;f=io/fcntl.h;h=3d239e8f0 9f7ce0a3106621be327e1ea4cd1a3e7;hb=23158b08a0908f381459f273a984c6fd3283 63cb#l142 And there's also AT_ANYNET and AT_ANYNODE from ddp (aka. AppleTalk) http://man7.org/linux/man-pages/man7/ddp.7.html Regards. -- Yann Droneaud OPTEYA