libvhost-user: support many virtqueues

Currently libvhost-user is hardcoded to at most 8 virtqueues.  The
device backend should decide the number of virtqueues, not
libvhost-user.  This is important for multiqueue device backends where
the guest driver needs an accurate number of virtqueues.

This change breaks libvhost-user and libvhost-user-glib API stability.
There is no stability guarantee yet, so make this change now and update
all in-tree library users.

This patch touches up vhost-user-blk, vhost-user-gpu, vhost-user-input,
vhost-user-scsi, and vhost-user-bridge.  If the device has a fixed
number of queues that exact number is used.  Otherwise the previous
default of 8 virtqueues is used.

vu_init() and vug_init() can now fail if malloc() returns NULL.  I
considered aborting with an error in libvhost-user but it should be safe
to instantiate new vhost-user instances at runtime without risk of
terminating the process.  Therefore callers need to handle the vu_init()
failure now.

vhost-user-blk and vhost-user-scsi duplicate virtqueue index checks that
are already performed by libvhost-user.  This code would need to be
modified to use max_queues but remove it completely instead since it's
redundant.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20190626074815.19994-3-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/contrib/libvhost-user/libvhost-user-glib.c b/contrib/libvhost-user/libvhost-user-glib.c
index 42660a1b36..99edd2f3de 100644
--- a/contrib/libvhost-user/libvhost-user-glib.c
+++ b/contrib/libvhost-user/libvhost-user-glib.c
@@ -131,18 +131,24 @@ static void vug_watch(VuDev *dev, int condition, void *data)
     }
 }
 
-void
-vug_init(VugDev *dev, int socket,
+bool
+vug_init(VugDev *dev, uint16_t max_queues, int socket,
          vu_panic_cb panic, const VuDevIface *iface)
 {
     g_assert(dev);
     g_assert(iface);
 
-    vu_init(&dev->parent, socket, panic, set_watch, remove_watch, iface);
+    if (!vu_init(&dev->parent, max_queues, socket, panic, set_watch,
+                 remove_watch, iface)) {
+        return false;
+    }
+
     dev->fdmap = g_hash_table_new_full(NULL, NULL, NULL,
                                        (GDestroyNotify) g_source_destroy);
 
     dev->src = vug_source_new(dev, socket, G_IO_IN, vug_watch, NULL);
+
+    return true;
 }
 
 void