Added basic support for FreeBSD.

Freebsd-support: Change bash shebang to use /usr/bin/env

Freebsd-support: Fix go vet "undefined" fixes when running make ci

freebsd: stub xattr functions

/proc/PID/fd does not exist on freebsd.

freebsd-support: modify FchmodatNofollow for FreeBSD

FreeBSD supports the Fchmodat system call, with the AT_SYMLINK_NOFOLLOW
flag. FchmodatNofollow has been modified to use this system call and
flag.

freebsd-support: PR changes and fixes

* Functions in fusefrontend_reverse/node_xattr_freebsd.go have been
  stubbed for now.

* asuser_freebsd.go updated to only run f() when context is nil;
  otherwise log a warning and return an error.

* emulate.go build flags updated, and FreeBSD specific version added.

* sys_freebsd.go bug in Renameat2 with RENAME_EXCHANGE flag fixed.
  FreeBSD does not support atomic file swapping, so this flag now
  returns an error.

* unix2syscall and atime is identical between FreeBSD and Darwin,
  updated filenames so Go will build the file for FreeBSD and Mac OS.

freebsd-support: Addressed more PR comments and fixed build tags

9 files changed, 16 insertions, 8 deletions

diff --git a/tests/canonical-benchmarks.bash b/tests/canonical-benchmarks.bash
index 4c1a357..963fd6a 100755
--- a/tests/canonical-benchmarks.bash
+++ b/tests/canonical-benchmarks.bash
@@ -1,4 +1,4 @@
-#!/bin/bash -eu
+#!/usr/bin/env bash
 #
 # Run the set of "canonical" benchmarks that are shown on
 # https://nuetzlich.net/gocryptfs/comparison/
@@ -6,6 +6,7 @@
 #
 # This is called by the top-level script "benchmark.bash".
 
+set -eu
 
 MYNAME=$(basename "$0")
 
diff --git a/tests/dl-linux-tarball.bash b/tests/dl-linux-tarball.bash
index 03c0e7d..3c325db 100755
--- a/tests/dl-linux-tarball.bash
+++ b/tests/dl-linux-tarball.bash
@@ -1,8 +1,10 @@
-#!/bin/bash -eu
+#!/usr/bin/env bash
 #
 # This script checks the size of /tmp/linux-3.0.tar.gz and downloads
 # a fresh copy if the size is incorrect or the file is missing.
 
+set -eu
+
 URL=https://cdn.kernel.org/pub/linux/kernel/v3.0/linux-3.0.tar.gz
 TGZ=/tmp/linux-3.0.tar.gz
 
diff --git a/tests/fuse-unmount.bash b/tests/fuse-unmount.bash
index b36f28c..02c6e4c 100755
--- a/tests/fuse-unmount.bash
+++ b/tests/fuse-unmount.bash
@@ -1,10 +1,13 @@
-#!/bin/bash -eu
+#!/usr/bin/env bash
 #
 # Compatibility wrapper around "fusermount" on Linux and "umount" on
 # Mac OS X and friends.
 #
 # This script can be sourced or executed directly.
 #
+
+set -eu
+
 fuse-unmount() {
 	local MYNAME=$(basename "$BASH_SOURCE")
 	if [[ $# -eq 0 ]] ; then
diff --git a/tests/matrix/atime_darwin.go b/tests/matrix/atime_darwin+freebsd.go
index 5f89c69..43db0d5 100644
--- a/tests/matrix/atime_darwin.go
+++ b/tests/matrix/atime_darwin+freebsd.go
@@ -1,3 +1,5 @@
+//go:build darwin || freebsd
+
 package matrix
 
 import (
diff --git a/tests/reverse/linux-tarball-test.bash b/tests/reverse/linux-tarball-test.bash
index 4054c29..27afa23 100755
--- a/tests/reverse/linux-tarball-test.bash
+++ b/tests/reverse/linux-tarball-test.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eu
 
diff --git a/tests/sshfs-benchmark.bash b/tests/sshfs-benchmark.bash
index 4695f8d..2421f20 100755
--- a/tests/sshfs-benchmark.bash
+++ b/tests/sshfs-benchmark.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eu
 
diff --git a/tests/stress_tests/extractloop.bash b/tests/stress_tests/extractloop.bash
index 1f78a5e..714d2d7 100755
--- a/tests/stress_tests/extractloop.bash
+++ b/tests/stress_tests/extractloop.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Mount a gocryptfs filesystem somewhere on /tmp, then run two parallel
 # infinite loops inside that do the following:
diff --git a/tests/stress_tests/fsstress-gocryptfs.bash b/tests/stress_tests/fsstress-gocryptfs.bash
index e6c3281..7e3f160 100755
--- a/tests/stress_tests/fsstress-gocryptfs.bash
+++ b/tests/stress_tests/fsstress-gocryptfs.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Mount a gocryptfs filesystem in /var/tmp and run fsstress against it
 # in an infinite loop, only exiting on errors.
diff --git a/tests/stress_tests/pingpong.bash b/tests/stress_tests/pingpong.bash
index d0d21b3..4fd5ff2 100755
--- a/tests/stress_tests/pingpong.bash
+++ b/tests/stress_tests/pingpong.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Mounts two gocryptfs filesystems, "ping" and "pong" and moves the
 # linux-3.0 kernel tree back and forth between them, checking integrity