Commits on Apr 26, 2018

1. cpython: don't use lchmod() on Linux, fix w/musl …

   upstream issue:
   https://bugs.python.org/issue31940
   
   There are two PR's proposed to fix this,
   but both seem to be stalling waiting for review.
   
   I previously used what appears to be the favored
   of the two approaches[1] to fix this,
   with plan of keeping it musl-only until PR was merged.
   
   However, while writing up a commit message
   explaining the problem and why it needed fixing...
   
   I investigated a bit and found it increasingly
   hard to justify anything other than ...
   simply not using lchmod.
   
   Here's what I found:
   * lchmod is non-POSIX, seems BSD-only these days
   * Functionality of lchmod isn't supported on Linux
     * best scenario on Linux would be an error
   * POSIX does provide lchmod-esque functionality
     with fchmodat(), which AFAICT is generally preferred.
   * Python intentionally overlooks fchmodat()[2]
     electing instead to use lchmod() behavior
     as a proxy for whether fchmodat() "works".
     I'm not sure I follow their reasoning...
   * both glibc and musl provide lchmod impls:
     * glibc returns ENOSYS "not implemented"
     * musl implements lchmod with fchmodat(),
       and so returns EOPNOTSUPP "op not supported"
   * Python doesn't expect EOPNOTSUPP from lchmod,
     since it's not valid on BSD's lchmod.
   * "configure" doesn't actually check lchmod usefully,
     instead checks for glibc preprocessor defines
     to indicate if the function is just a stub[3];
     somewhat fittingly, if the magic macros are defined
     then the next line of the C source is "choke me",
     causing the compiler to trip, fall, and point
     a finger at whatever is near where it ends up.
     (somewhat amusing, but AFAIK effective way to get an error :P)
   
   I'm leaving out links to threads on mailing lists and such,
   but for now I hope I've convinced you
   (or to those reading commit history: explained my reasons)
   that this is a bit of a mess[4].
   
   And so instead of making a big mess messier,
   and with hopes of never thinking about this again,
   I propose we simply tell Python "don't use lchmod" on Linux.
   
   [1] python/cpython#4783
   [2] https://github.com/python/cpython/blob/28453feaa8d88bbcbf6d834b1d5ca396d17265f2/Lib/os.py#L144
   [3] https://github.com/python/cpython/blob/28453feaa8d88bbcbf6d834b1d5ca396d17265f2/configure#L2198
   [4] Messes happen, no good intention goes unpunished :).

   

   dtzWill committed Apr 26, 2018
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2. Merge pull request #39517 from dtzWill/fix/python3.x-musl-lchmod …

   cpython: don't use lchmod() on Linux, fix w/musl

   

   dtzWill committed Apr 26, 2018
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