xen: register legacy backends via xen_backend_init

It is okay to register legacy backends in the middle of xen_bus_init().
All that the registration does is record the existence of the backend
in xenstore.

This makes it possible to remove them from the build without introducing
undefined symbols in xen_be_init().  It also removes the need for the
backend_register callback, whose only purpose is to avoid registering
nonfunctional backends.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240509170044.190795-8-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c
index 4aa9c8c736..a3ac53f989 100644
--- a/hw/9pfs/xen-9p-backend.c
+++ b/hw/9pfs/xen-9p-backend.c
@@ -513,7 +513,7 @@ static void xen_9pfs_alloc(struct XenLegacyDevice *xendev)
     xenstore_write_be_int(xendev, "max-ring-page-order", MAX_RING_ORDER);
 }
 
-struct XenDevOps xen_9pfs_ops = {
+static struct XenDevOps xen_9pfs_ops = {
     .size       = sizeof(Xen9pfsDev),
     .flags      = DEVOPS_FLAG_NEED_GNTDEV,
     .alloc      = xen_9pfs_alloc,
@@ -522,3 +522,9 @@ struct XenDevOps xen_9pfs_ops = {
     .disconnect = xen_9pfs_disconnect,
     .free       = xen_9pfs_free,
 };
+
+static void xen_9pfs_register_backend(void)
+{
+    xen_be_register("9pfs", &xen_9pfs_ops);
+}
+xen_backend_init(xen_9pfs_register_backend);