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

14 files changed, 271 insertions, 4 deletions

diff --git a/internal/fusefrontend/node_xattr_freebsd.go b/internal/fusefrontend/node_xattr_freebsd.go
new file mode 100644
index 0000000..9698283
--- /dev/null
+++ b/internal/fusefrontend/node_xattr_freebsd.go
@@ -0,0 +1,33 @@
+package fusefrontend
+
+import (
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+)
+
+const noSuchAttributeError = unix.ENOATTR
+
+func filterXattrSetFlags(flags int) int {
+	return flags
+}
+
+func (n *Node) getXAttr(cAttr string) (out []byte, errno unix.Errno) {
+	// TODO
+	return nil, unix.EOPNOTSUPP
+}
+
+func (n *Node) setXAttr(context *fuse.Context, cAttr string, cData []byte, flags uint32) (errno unix.Errno) {
+	// TODO
+	return unix.EOPNOTSUPP
+}
+
+func (n *Node) removeXAttr(cAttr string) (errno unix.Errno) {
+	// TODO
+	return unix.EOPNOTSUPP
+}
+
+func (n *Node) listXAttr() (out []string, errno unix.Errno) {
+	// TODO
+	return nil, unix.EOPNOTSUPP
+}
diff --git a/internal/fusefrontend_reverse/node_xattr_freebsd.go b/internal/fusefrontend_reverse/node_xattr_freebsd.go
new file mode 100644
index 0000000..949cf15
--- /dev/null
+++ b/internal/fusefrontend_reverse/node_xattr_freebsd.go
@@ -0,0 +1,17 @@
+package fusefrontend_reverse
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+const noSuchAttributeError = unix.ENOATTR
+
+func (n *Node) getXAttr(cAttr string) (out []byte, errno unix.Errno) {
+	// TODO
+	return nil, unix.EOPNOTSUPP
+}
+
+func (n *Node) listXAttr() (out []string, errno unix.Errno) {
+	// TODO
+	return nil, unix.EOPNOTSUPP
+}
diff --git a/internal/siv_aead/benchmark.bash b/internal/siv_aead/benchmark.bash
index 40b57b3..400c134 100755
--- a/internal/siv_aead/benchmark.bash
+++ b/internal/siv_aead/benchmark.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eu
 
diff --git a/internal/speed/benchmark.bash b/internal/speed/benchmark.bash
index d2678a7..699ceb8 100755
--- a/internal/speed/benchmark.bash
+++ b/internal/speed/benchmark.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eu
 
diff --git a/internal/stupidgcm/benchmark.bash b/internal/stupidgcm/benchmark.bash
index 8681495..8319659 100755
--- a/internal/stupidgcm/benchmark.bash
+++ b/internal/stupidgcm/benchmark.bash
@@ -1,3 +1,3 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 exec ../speed/benchmark.bash
diff --git a/internal/syscallcompat/asuser_freebsd.go b/internal/syscallcompat/asuser_freebsd.go
new file mode 100644
index 0000000..dfa8e18
--- /dev/null
+++ b/internal/syscallcompat/asuser_freebsd.go
@@ -0,0 +1,24 @@
+package syscallcompat
+
+import (
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
+)
+
+// asUser runs `f()` under the effective uid, gid, groups specified
+// in `context`.
+//
+// If `context` is nil, `f()` is executed directly without switching user id.
+//
+// FreeBSD does not support changing uid/gid per thread. If context is not nil,
+// an error is returned.
+func asUser(f func() (int, error), context *fuse.Context) (int, error) {
+	if context == nil {
+		return f()
+	}
+	tlog.Warn.Printf("asUser: error, only nil context is supported\n")
+	return 0, unix.EOPNOTSUPP
+}
diff --git a/internal/syscallcompat/emulate.go b/internal/syscallcompat/emulate.go
index 91b592b..435c579 100644
--- a/internal/syscallcompat/emulate.go
+++ b/internal/syscallcompat/emulate.go
@@ -1,3 +1,5 @@
+//go:build !freebsd
+
 package syscallcompat
 
 import (
diff --git a/internal/syscallcompat/emulate_test.go b/internal/syscallcompat/emulate_test.go
index 16383f2..907ba3a 100644
--- a/internal/syscallcompat/emulate_test.go
+++ b/internal/syscallcompat/emulate_test.go
@@ -1,3 +1,5 @@
+//go:build !freebsd
+
 package syscallcompat
 
 import (
diff --git a/internal/syscallcompat/quirks_freebsd.go b/internal/syscallcompat/quirks_freebsd.go
new file mode 100644
index 0000000..c340cea
--- /dev/null
+++ b/internal/syscallcompat/quirks_freebsd.go
@@ -0,0 +1,22 @@
+package syscallcompat
+
+import (
+	"golang.org/x/sys/unix"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
+)
+
+// DetectQuirks decides if there are known quirks on the backing filesystem
+// that need to be workarounded.
+//
+// Tested by tests/root_test.TestBtrfsQuirks
+func DetectQuirks(cipherdir string) (q uint64) {
+	var st unix.Statfs_t
+	err := unix.Statfs(cipherdir, &st)
+	if err != nil {
+		tlog.Warn.Printf("DetectQuirks: Statfs on %q failed: %v", cipherdir, err)
+		return 0
+	}
+
+	return q
+}
diff --git a/internal/syscallcompat/sys_common.go b/internal/syscallcompat/sys_common.go
index 3cb9ffa..4f84d98 100644
--- a/internal/syscallcompat/sys_common.go
+++ b/internal/syscallcompat/sys_common.go
@@ -138,7 +138,7 @@ func getxattrSmartBuf(fn func(buf []byte) (int, error)) ([]byte, error) {
 	buf := make([]byte, GETXATTR_BUFSZ_SMALL)
 	sz, err := fn(buf)
 	// Non-existing xattr
-	if err == unix.ENODATA {
+	if err == ENODATA {
 		return nil, err
 	}
 	// Underlying fs does not support security.capabilities (example: tmpfs)
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index ef19f24..52d4e0f 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -24,6 +24,8 @@ const (
 	RENAME_NOREPLACE = unix.RENAME_EXCL
 	RENAME_EXCHANGE  = unix.RENAME_SWAP
 
+	ENODATA = unix.ENODATA
+
 	// Only exists on Linux. Define here to fix build failure, even though
 	// we will never see this flag.
 	RENAME_WHITEOUT = 1 << 30
diff --git a/internal/syscallcompat/sys_freebsd.go b/internal/syscallcompat/sys_freebsd.go
new file mode 100644
index 0000000..d88b1cf
--- /dev/null
+++ b/internal/syscallcompat/sys_freebsd.go
@@ -0,0 +1,160 @@
+// Package syscallcompat wraps FreeBSD-specific syscalls
+package syscallcompat
+
+import (
+	"time"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
+)
+
+const (
+	O_DIRECT = unix.O_DIRECT
+
+	// O_PATH is supported on FreeBSD, but is missing from the sys/unix package
+	// FreeBSD-15.0 /usr/src/sys/sys/fcntl.h:135
+	O_PATH = 0x00400000
+
+	// Only defined on Linux, but we can emulate the functionality on FreeBSD
+	// in Renameat2() below
+	RENAME_NOREPLACE = 0x1
+	RENAME_EXCHANGE  = 0x2
+	RENAME_WHITEOUT  = 0x4
+
+	// ENODATA is only defined on Linux, but FreeBSD provides ENOATTR
+	ENODATA = unix.ENOATTR
+
+	// On FreeBSD, we only have O_NOFOLLOW.
+	OpenatFlagNofollowSymlink = unix.O_NOFOLLOW
+
+	// For the utimensat syscall on FreeBSD
+	AT_EMPTY_PATH = 0x4000
+)
+
+// EnospcPrealloc is supposed to preallocate ciphertext space without
+// changing the file size. This guarantees that we don't run out of
+// space while writing a ciphertext block (that would corrupt the block).
+//
+// The fallocate syscall isn't supported on FreeBSD with the same semantics
+// as Linux, in particular the _FALLOC_FL_KEEP_SIZE mode isn't supported.
+func EnospcPrealloc(fd int, off int64, len int64) (err error) {
+	return nil
+}
+
+// Fallocate wraps the posix_fallocate() syscall.
+// Fallocate returns an error if mode is not 0
+func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
+	if mode != 0 {
+		tlog.Warn.Printf("Fallocate: unsupported mode\n")
+		return unix.EOPNOTSUPP
+	}
+	_, _, err = unix.Syscall(unix.SYS_POSIX_FALLOCATE, uintptr(fd), uintptr(off), uintptr(len))
+	return err
+}
+
+// Mknodat wraps the Mknodat syscall.
+func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
+	return unix.Mknodat(dirfd, path, mode, uint64(dev))
+}
+
+// Dup3 wraps the Dup3 syscall. We want to use Dup3 rather than Dup2 because Dup2
+// is not implemented on arm64.
+func Dup3(oldfd int, newfd int, flags int) (err error) {
+	return unix.Dup3(oldfd, newfd, flags)
+}
+
+// FchmodatNofollow is like Fchmodat but never follows symlinks.
+func FchmodatNofollow(dirfd int, path string, mode uint32) (err error) {
+	return unix.Fchmodat(dirfd, path, mode, unix.AT_SYMLINK_NOFOLLOW)
+}
+
+// LsetxattrUser runs the Lsetxattr syscall in the context of a different user.
+// This is useful when setting ACLs, as the result depends on the user running
+// the operation (see fuse-xfstests generic/375).
+//
+// If `context` is nil, this function behaves like ordinary Lsetxattr.
+func LsetxattrUser(path string, attr string, data []byte, flags int, context *fuse.Context) (err error) {
+	f := func() (int, error) {
+		err := unix.Lsetxattr(path, attr, data, flags)
+		return -1, err
+	}
+	_, err = asUser(f, context)
+	return err
+}
+
+func timesToTimespec(a *time.Time, m *time.Time) []unix.Timespec {
+	ts := make([]unix.Timespec, 2)
+	if a == nil {
+		ts[0] = unix.Timespec{Nsec: unix.UTIME_OMIT}
+	} else {
+		ts[0], _ = unix.TimeToTimespec(*a)
+	}
+	if m == nil {
+		ts[1] = unix.Timespec{Nsec: unix.UTIME_OMIT}
+	} else {
+		ts[1], _ = unix.TimeToTimespec(*m)
+	}
+	return ts
+}
+
+// FutimesNano syscall.
+func FutimesNano(fd int, a *time.Time, m *time.Time) (err error) {
+	ts := timesToTimespec(a, m)
+	return unix.UtimesNanoAt(unix.AT_FDCWD, "", ts, AT_EMPTY_PATH)
+}
+
+// UtimesNanoAtNofollow is like UtimesNanoAt but never follows symlinks.
+// Retries on EINTR.
+func UtimesNanoAtNofollow(dirfd int, path string, a *time.Time, m *time.Time) (err error) {
+	ts := timesToTimespec(a, m)
+	err = retryEINTR(func() error {
+		return unix.UtimesNanoAt(dirfd, path, ts, unix.AT_SYMLINK_NOFOLLOW)
+	})
+	return err
+}
+
+// Getdents syscall with "." and ".." filtered out.
+func Getdents(fd int) ([]fuse.DirEntry, error) {
+	entries, _, err := emulateGetdents(fd)
+	return entries, err
+}
+
+// GetdentsSpecial calls the Getdents syscall,
+// with normal entries and "." / ".." split into two slices.
+func GetdentsSpecial(fd int) (entries []fuse.DirEntry, entriesSpecial []fuse.DirEntry, err error) {
+	return emulateGetdents(fd)
+}
+
+// Renameat2 does not exist on FreeBSD, so we have to wrap it here.
+// Retries on EINTR.
+// The RENAME_EXCHANGE and RENAME_WHITEOUT flags are not supported.
+func Renameat2(olddirfd int, oldpath string, newdirfd int, newpath string, flags uint) (err error) {
+	if flags&(RENAME_NOREPLACE|RENAME_EXCHANGE) == RENAME_NOREPLACE|RENAME_EXCHANGE {
+		return unix.EINVAL
+	}
+	if flags&(RENAME_NOREPLACE|RENAME_EXCHANGE) == RENAME_NOREPLACE|RENAME_EXCHANGE {
+		return unix.EINVAL
+	}
+
+	if flags&RENAME_NOREPLACE != 0 {
+		var st unix.Stat_t
+		err = unix.Fstatat(newdirfd, newpath, &st, 0)
+		if err == nil {
+			// Assume newpath is an existing file if we can stat() it.
+			// On Linux, RENAME_NOREPLACE fails with EEXIST if newpath
+			// already exists.
+			return unix.EEXIST
+		}
+	}
+	if flags&RENAME_EXCHANGE != 0 {
+		return unix.EINVAL
+	}
+	if flags&RENAME_WHITEOUT != 0 {
+		return unix.EINVAL
+	}
+
+	return unix.Renameat(olddirfd, oldpath, newdirfd, newpath)
+}
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 71478af..a850ba1 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -32,6 +32,9 @@ const (
 	// On Darwin we use O_SYMLINK which allows opening a symlink itself.
 	// On Linux, we only have O_NOFOLLOW.
 	OpenatFlagNofollowSymlink = unix.O_NOFOLLOW
+
+	// Only defined on Linux
+	ENODATA = unix.ENODATA
 )
 
 var preallocWarn sync.Once
diff --git a/internal/syscallcompat/unix2syscall_darwin.go b/internal/syscallcompat/unix2syscall.go
index 5767a27..fa2e8c4 100644
--- a/internal/syscallcompat/unix2syscall_darwin.go
+++ b/internal/syscallcompat/unix2syscall.go
@@ -1,3 +1,5 @@
+//go:build darwin || freebsd
+
 package syscallcompat
 
 import (