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

1 files changed, 160 insertions, 0 deletions

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)
+}