qemu-char: cleanup HAVE_CHARDEV_*

Move the #ifdef up into qmp_chardev_add, and avoid duplicating
the code that reports unavailable backends.  Split HAVE_CHARDEV_TTY
into HAVE_CHARDEV_SERIAL and HAVE_CHARDEV_PTY.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-char.c

diff --git a/qemu-char.c b/qemu-char.c
index f51c0aa..7219d56 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1196,7 +1196,8 @@
     || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) \
     || defined(__GLIBC__)
 
-#define HAVE_CHARDEV_TTY 1
+#define HAVE_CHARDEV_SERIAL 1
+#define HAVE_CHARDEV_PTY 1
 
 typedef struct {
     GIOChannel *fd;
@@ -1832,6 +1833,8 @@
 
 #else /* _WIN32 */
 
+#define HAVE_CHARDEV_SERIAL 1
+
 typedef struct {
     int max_size;
     HANDLE hcom, hrecv, hsend;
@@ -4069,10 +4072,10 @@
     return qemu_chr_open_fd(in, out);
 }
 
+#ifdef HAVE_CHARDEV_SERIAL
 static CharDriverState *qmp_chardev_open_serial(ChardevHostdev *serial,
                                                 Error **errp)
 {
-#ifdef HAVE_CHARDEV_TTY
     int fd;
 
     fd = qmp_chardev_open_file_source(serial->device, O_RDWR, errp);
@@ -4081,16 +4084,12 @@
     }
     qemu_set_nonblock(fd);
     return qemu_chr_open_tty_fd(fd);
-#else
-    error_setg(errp, "character device backend type 'serial' not supported");
-    return NULL;
-#endif
 }
 
+#ifdef HAVE_CHARDEV_PARPORT
 static CharDriverState *qmp_chardev_open_parallel(ChardevHostdev *parallel,
                                                   Error **errp)
 {
-#ifdef HAVE_CHARDEV_PARPORT
     int fd;
 
     fd = qmp_chardev_open_file_source(parallel->device, O_RDWR, errp);
@@ -4098,11 +4097,8 @@
         return NULL;
     }
     return qemu_chr_open_pp_fd(fd);
-#else
-    error_setg(errp, "character device backend type 'parallel' not supported");
-    return NULL;
-#endif
 }
+#endif
 
 #endif /* WIN32 */
 
@@ -4227,12 +4223,16 @@
     case CHARDEV_BACKEND_KIND_FILE:
         chr = qmp_chardev_open_file(backend->file, &local_err);
         break;
+#ifdef HAVE_CHARDEV_SERIAL
     case CHARDEV_BACKEND_KIND_SERIAL:
         chr = qmp_chardev_open_serial(backend->serial, &local_err);
         break;
+#endif
+#ifdef HAVE_CHARDEV_PARPORT
     case CHARDEV_BACKEND_KIND_PARALLEL:
         chr = qmp_chardev_open_parallel(backend->parallel, &local_err);
         break;
+#endif
     case CHARDEV_BACKEND_KIND_PIPE:
         chr = qemu_chr_open_pipe(backend->pipe);
         break;
@@ -4242,7 +4242,7 @@
     case CHARDEV_BACKEND_KIND_UDP:
         chr = qmp_chardev_open_udp(backend->udp, &local_err);
         break;
-#ifdef HAVE_CHARDEV_TTY
+#ifdef HAVE_CHARDEV_PTY
     case CHARDEV_BACKEND_KIND_PTY:
         chr = qemu_chr_open_pty(id, ret);
         break;