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, 10 insertions, 1 deletions

diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
index 8b4e7d2..449fd21 100644
--- a/contrib/vhost-user-input/main.c
+++ b/contrib/vhost-user-input/main.c
@@ -17,6 +17,10 @@
 #include "standard-headers/linux/virtio_input.h"
 #include "qapi/error.h"
 
+enum {
+    VHOST_USER_INPUT_MAX_QUEUES = 2,
+};
+
 typedef struct virtio_input_event virtio_input_event;
 typedef struct virtio_input_config virtio_input_config;
 
@@ -384,7 +388,12 @@ main(int argc, char *argv[])
         g_printerr("Invalid vhost-user socket.\n");
         exit(EXIT_FAILURE);
     }
-    vug_init(&vi.dev, fd, vi_panic, &vuiface);
+
+    if (!vug_init(&vi.dev, VHOST_USER_INPUT_MAX_QUEUES, fd, vi_panic,
+                  &vuiface)) {
+        g_printerr("Failed to initialize libvhost-user-glib.\n");
+        exit(EXIT_FAILURE);
+    }
 
     loop = g_main_loop_new(NULL, FALSE);
     g_main_loop_run(loop);