9p: Simplify error path of v9fs_device_realize_common()

Make v9fs_device_unrealize_common() idempotent and use it for rollback,
in order to reduce code duplication.

Signed-off-by: Greg Kurz <groug@kaod.org>

hw/9pfs/9p-local.c

@@ -1465,6 +1465,10 @@ static void local_cleanup(FsContext *ctx)
 {
     LocalData *data = ctx->private;
 
+    if (!data) {
+        return;
+    }
+
     close(data->mountfd);
     g_free(data);
 }

hw/9pfs/9p-proxy.c

@@ -1185,6 +1185,10 @@ static void proxy_cleanup(FsContext *ctx)
 {
     V9fsProxy *proxy = ctx->private;
 
+    if (!proxy) {
+        return;
+    }
+
     g_free(proxy->out_iovec.iov_base);
     g_free(proxy->in_iovec.iov_base);
     if (ctx->export_flags & V9FS_PROXY_SOCK_NAME) {

hw/9pfs/9p.c

@@ -3637,27 +3637,23 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t,
     s->ctx.fst = &fse->fst;
     fsdev_throttle_init(s->ctx.fst);
 
-    v9fs_path_free(&path);
-
     rc = 0;
 out:
     if (rc) {
-        if (s->ops && s->ops->cleanup && s->ctx.private) {
-            s->ops->cleanup(&s->ctx);
-        }
-        g_free(s->tag);
-        g_free(s->ctx.fs_root);
-        v9fs_path_free(&path);
+        v9fs_device_unrealize_common(s, NULL);
     }
+    v9fs_path_free(&path);
     return rc;
 }
 
 void v9fs_device_unrealize_common(V9fsState *s, Error **errp)
 {
-    if (s->ops->cleanup) {
+    if (s->ops && s->ops->cleanup) {
         s->ops->cleanup(&s->ctx);
     }
-    fsdev_throttle_cleanup(s->ctx.fst);
+    if (s->ctx.fst) {
+        fsdev_throttle_cleanup(s->ctx.fst);
+    }
     g_free(s->tag);
     g_free(s->ctx.fs_root);
 }