[PATCH] D30010: Improve the robustness of mmap

[Zachary Turner via Phabricator via llvm-commits]

zturner created this revision.
Herald added subscribers: srhines, danalbert.

When we mmap a file, we don't take into consideration whether the file is on a remote share.  mmaping such a file is problematic because if the network share goes away -- which can happen for reasons outside of the user's control -- anything trying to read from that file will have undefined behavior.

LLDB already has logic to check whether a file is local or remote, but it was not implemented on Windows.

Also, `mmap` on newer versions of OSX have some additional flags which LLDB requires and which I see no reason to ever NOT include even for general usage, so the low level call to `mmap` is udpated to use those flags when available.

Note that I do not have **any** non-Windows machine to test on, so I'm including a lot of people from various platforms here to look over this:

Getting the `statvfs` / `statfs` distiction correct was tricky, but hopefully I got this correct.  FWIU,

NetBSD: `statfs` does not exist!  Must use `statvfs` for everything.  Reference <http://netbsd.gw.com/cgi-bin/man-cgi?statvfs+2+NetBSD-current>
FreeBSD: `statvfs::f_flag` does not contain `MNT_LOCAL`.  Must use `statfs`.  Reference <https://www.freebsd.org/cgi/man.cgi?query=statvfs>
OpenBSD: Both functions exist, but documentation does not specify whether the flags differ between the two.

Since FreeBSD cannot use `statvfs` to check for `MNT_LOCAL`, I'm adjusting the conditional in `Path.inc` so that `FreeBSD` and `OpenBSD` follow the same codepath.  Nothing was broken before, it's only now that we need to use `f_flag & MNT_LOCAL` that FreeBSD requires a change to use `statfs` instead.


https://reviews.llvm.org/D30010

Files:
  llvm/include/llvm/Support/FileSystem.h
  llvm/lib/Support/MemoryBuffer.cpp
  llvm/lib/Support/Unix/Path.inc
  llvm/lib/Support/Windows/Path.inc
  llvm/unittests/Support/Path.cpp

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