freebsd: add initial support for running on FreeBSD, excluding Bluez,

ppd, and some things. Add a simple wpa_supplicant backend

core/internal/wayland/shm/fd_freebsd.go

@@ -0,0 +1,28 @@
+package shm
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// Mirrors FreeBSD libc memfd_create (lib/libc/gen/memfd_create.c):
+// shm_open2(SHM_ANON, O_RDWR, 0, SHM_GROW_ON_WRITE, name).
+// x/sys/unix has no wrapper for SYS_shm_open2 (571, sys/sys/syscall.h).
+const (
+	sysShmOpen2    = 571
+	shmAnon        = 1   // SHM_ANON ((char *)1), sys/sys/mman.h
+	shmGrowOnWrite = 0x2 // SHM_GROW_ON_WRITE, sys/sys/mman.h
+)
+
+func CreateAnonFd(name string) (int, error) {
+	p, err := unix.BytePtrFromString(name)
+	if err != nil {
+		return -1, err
+	}
+	fd, _, errno := unix.Syscall6(sysShmOpen2, shmAnon, unix.O_RDWR, 0, shmGrowOnWrite, uintptr(unsafe.Pointer(p)), 0)
+	if errno != 0 {
+		return -1, errno
+	}
+	return int(fd), nil
+}