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, 7 insertions, 3 deletions

diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 3b888ff0a5..46b600799b 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -25,7 +25,6 @@
 #define VHOST_USER_F_PROTOCOL_FEATURES 30
 #define VHOST_LOG_PAGE 4096
 
-#define VHOST_MAX_NR_VIRTQUEUE 8
 #define VIRTQUEUE_MAX_SIZE 1024
 
 #define VHOST_MEMORY_MAX_NREGIONS 8
@@ -353,7 +352,7 @@ struct VuDev {
     int sock;
     uint32_t nregions;
     VuDevRegion regions[VHOST_MEMORY_MAX_NREGIONS];
-    VuVirtq vq[VHOST_MAX_NR_VIRTQUEUE];
+    VuVirtq *vq;
     VuDevInflightInfo inflight_info;
     int log_call_fd;
     int slave_fd;
@@ -362,6 +361,7 @@ struct VuDev {
     uint64_t features;
     uint64_t protocol_features;
     bool broken;
+    uint16_t max_queues;
 
     /* @set_watch: add or update the given fd to the watch set,
      * call cb when condition is met */
@@ -391,6 +391,7 @@ typedef struct VuVirtqElement {
 /**
  * vu_init:
  * @dev: a VuDev context
+ * @max_queues: maximum number of virtqueues
  * @socket: the socket connected to vhost-user master
  * @panic: a panic callback
  * @set_watch: a set_watch callback
@@ -398,8 +399,11 @@ typedef struct VuVirtqElement {
  * @iface: a VuDevIface structure with vhost-user device callbacks
  *
  * Intializes a VuDev vhost-user context.
+ *
+ * Returns: true on success, false on failure.
  **/
-void vu_init(VuDev *dev,
+bool vu_init(VuDev *dev,
+             uint16_t max_queues,
              int socket,
              vu_panic_cb panic,
              vu_set_watch_cb set_watch,