virtio/vhost-user: dynamically assign VhostUserHostNotifiers

At a couple of hundred bytes per notifier allocating one for every
potential queue is very wasteful as most devices only have a few
queues. Instead of having this handled statically dynamically assign
them and track in a GPtrArray.

[AJB: it's hard to trigger the vhost notifiers code, I assume as it
requires a KVM guest with appropriate backend]

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220321153037.3622127-14-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 41 insertions, 1 deletions

diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
index 6e0e8a71a3..c6e693cd3f 100644
--- a/include/hw/virtio/vhost-user.h
+++ b/include/hw/virtio/vhost-user.h
@@ -11,21 +11,61 @@
 #include "chardev/char-fe.h"
 #include "hw/virtio/virtio.h"
 
+/**
+ * VhostUserHostNotifier - notifier information for one queue
+ * @rcu: rcu_head for cleanup
+ * @mr: memory region of notifier
+ * @addr: current mapped address
+ * @unmap_addr: address to be un-mapped
+ * @idx: virtioqueue index
+ *
+ * The VhostUserHostNotifier entries are re-used. When an old mapping
+ * is to be released it is moved to @unmap_addr and @addr is replaced.
+ * Once the RCU process has completed the unmap @unmap_addr is
+ * cleared.
+ */
 typedef struct VhostUserHostNotifier {
     struct rcu_head rcu;
     MemoryRegion mr;
     void *addr;
     void *unmap_addr;
+    int idx;
 } VhostUserHostNotifier;
 
+/**
+ * VhostUserState - shared state for all vhost-user devices
+ * @chr: the character backend for the socket
+ * @notifiers: GPtrArray of @VhostUserHostnotifier
+ * @memory_slots:
+ */
 typedef struct VhostUserState {
     CharBackend *chr;
-    VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX];
+    GPtrArray *notifiers;
     int memory_slots;
     bool supports_config;
 } VhostUserState;
 
+/**
+ * vhost_user_init() - initialise shared vhost_user state
+ * @user: allocated area for storing shared state
+ * @chr: the chardev for the vhost socket
+ * @errp: error handle
+ *
+ * User can either directly g_new() space for the state or embed
+ * VhostUserState in their larger device structure and just point to
+ * it.
+ *
+ * Return: true on success, false on error while setting errp.
+ */
 bool vhost_user_init(VhostUserState *user, CharBackend *chr, Error **errp);
+
+/**
+ * vhost_user_cleanup() - cleanup state
+ * @user: ptr to use state
+ *
+ * Cleans up shared state and notifiers, callee is responsible for
+ * freeing the @VhostUserState memory itself.
+ */
 void vhost_user_cleanup(VhostUserState *user);
 
 #endif