[Qemu-devel] [PATCH v4 12/22] vhost: only use shared log if in use by backend

[marcandre.lureau@redhat.com]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Do not allocate a shared log if the backend doesn't support it.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 hw/virtio/vhost-user.c            |  9 +++++++++
 hw/virtio/vhost.c                 | 15 ++++++++++-----
 include/hw/virtio/vhost-backend.h |  4 ++++
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 3cb5559..d12cd66 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -508,10 +508,19 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
     return 0;
 }
 
+static bool vhost_user_want_shm_log(struct vhost_dev *dev)
+{
+    assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
+
+    return virtio_has_feature(dev->protocol_features,
+                              VHOST_USER_PROTOCOL_F_LOG_SHMFD);
+}
+
 const VhostOps user_ops = {
         .backend_type = VHOST_BACKEND_TYPE_USER,
         .vhost_backend_init = vhost_user_init,
         .vhost_backend_cleanup = vhost_user_cleanup,
+        .vhost_backend_want_shm_log = vhost_user_want_shm_log,
 
         .vhost_net_set_backend = vhost_net_set_backend,
         .vhost_scsi_set_endpoint = vhost_scsi_set_endpoint,
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 0fa7b69..d5070fb 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -350,10 +350,15 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
     }
 }
 
-static inline void vhost_dev_log_resize(struct vhost_dev* dev, uint64_t size)
+static bool vhost_dev_log_is_shared(struct vhost_dev *dev)
 {
-    bool share = dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER;
-    struct vhost_log *log = vhost_log_get(size, share);
+    return dev->vhost_ops->vhost_backend_want_shm_log &&
+           dev->vhost_ops->vhost_backend_want_shm_log(dev);
+}
+
+static inline void vhost_dev_log_resize(struct vhost_dev *dev, uint64_t size)
+{
+    struct vhost_log *log = vhost_log_get(size, vhost_dev_log_is_shared(dev));
     uint64_t log_base = (uintptr_t)log->log;
     int r;
 
@@ -1161,10 +1166,10 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
 
     if (hdev->log_enabled) {
         uint64_t log_base;
-        bool share = hdev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER;
 
         hdev->log_size = vhost_get_log_size(hdev);
-        hdev->log = vhost_log_get(hdev->log_size, share);
+        hdev->log = vhost_log_get(hdev->log_size,
+                                  vhost_dev_log_is_shared(hdev));
         log_base = (uintptr_t)hdev->log->log;
         r = hdev->vhost_ops->vhost_set_log_base(hdev,
                                                 hdev->log_size ? log_base : 0,
diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
index a87f0b3..44bf200 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -11,6 +11,8 @@
 #ifndef VHOST_BACKEND_H_
 #define VHOST_BACKEND_H_
 
+#include <stdbool.h>
+
 typedef enum VhostBackendType {
     VHOST_BACKEND_TYPE_NONE = 0,
     VHOST_BACKEND_TYPE_KERNEL = 1,
@@ -28,6 +30,7 @@ struct vhost_scsi_target;
 
 typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
 typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
+typedef bool (*vhost_backend_want_shm_log)(struct vhost_dev *dev);
 
 typedef int (*vhost_net_set_backend_op)(struct vhost_dev *dev,
                                         struct vhost_vring_file *file);
@@ -67,6 +70,7 @@ typedef struct VhostOps {
 
     vhost_backend_init vhost_backend_init;
     vhost_backend_cleanup vhost_backend_cleanup;
+    vhost_backend_want_shm_log vhost_backend_want_shm_log;
 
     vhost_net_set_backend_op vhost_net_set_backend;
     vhost_scsi_set_endpoint_op vhost_scsi_set_endpoint;
-- 
2.4.3