[PATCH v4 4/9] vhost_user: Add frontend get_shmem_config command

[Albert Esteve <aesteve@redhat.com>]

The frontend can use this command to retrieve
VirtIO Shared Memory Regions configuration from
the backend. The response contains the number of
shared memory regions, their size, and shmid.

This is useful when the frontend is unaware of
specific backend type and configuration,
for example, in the `vhost-user-device` case.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 hw/virtio/vhost-user.c            | 43 +++++++++++++++++++++++++++++++
 include/hw/virtio/vhost-backend.h |  9 +++++++
 include/hw/virtio/vhost-user.h    |  1 +
 include/hw/virtio/virtio.h        |  2 ++
 4 files changed, 55 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index d88e6f8c3c..9cc148f726 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -104,6 +104,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_SHARED_OBJECT = 41,
     VHOST_USER_SET_DEVICE_STATE_FD = 42,
     VHOST_USER_CHECK_DEVICE_STATE = 43,
+    VHOST_USER_GET_SHMEM_CONFIG = 44,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -138,6 +139,12 @@ typedef struct VhostUserMemRegMsg {
     VhostUserMemoryRegion region;
 } VhostUserMemRegMsg;
 
+typedef struct VhostUserShMemConfig {
+    uint32_t nregions;
+    uint32_t padding;
+    uint64_t memory_sizes[VIRTIO_MAX_SHMEM_REGIONS];
+} VhostUserShMemConfig;
+
 typedef struct VhostUserLog {
     uint64_t mmap_size;
     uint64_t mmap_offset;
@@ -245,6 +252,7 @@ typedef union {
         VhostUserShared object;
         VhostUserTransferDeviceState transfer_state;
         VhostUserMMap mmap;
+        VhostUserShMemConfig shmem;
 } VhostUserPayload;
 
 typedef struct VhostUserMsg {
@@ -3146,6 +3154,40 @@ static int vhost_user_check_device_state(struct vhost_dev *dev, Error **errp)
     return 0;
 }
 
+static int vhost_user_get_shmem_config(struct vhost_dev *dev,
+                                       int *nregions,
+                                       uint64_t *memory_sizes,
+                                       Error **errp)
+{
+    int ret;
+    VhostUserMsg msg = {
+        .hdr.request = VHOST_USER_GET_SHMEM_CONFIG,
+        .hdr.flags = VHOST_USER_VERSION,
+    };
+
+    if (!virtio_has_feature(dev->protocol_features,
+                            VHOST_USER_PROTOCOL_F_SHMEM)) {
+        return 0;
+    }
+
+    ret = vhost_user_write(dev, &msg, NULL, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = vhost_user_read(dev, &msg);
+    if (ret < 0) {
+        return ret;
+    }
+
+    assert(msg.payload.shmem.nregions <= VIRTIO_MAX_SHMEM_REGIONS);
+    *nregions = msg.payload.shmem.nregions;
+    memcpy(memory_sizes,
+           &msg.payload.shmem.memory_sizes,
+           sizeof(uint64_t) * VHOST_MEMORY_BASELINE_NREGIONS);
+    return 0;
+}
+
 const VhostOps user_ops = {
         .backend_type = VHOST_BACKEND_TYPE_USER,
         .vhost_backend_init = vhost_user_backend_init,
@@ -3184,4 +3226,5 @@ const VhostOps user_ops = {
         .vhost_supports_device_state = vhost_user_supports_device_state,
         .vhost_set_device_state_fd = vhost_user_set_device_state_fd,
         .vhost_check_device_state = vhost_user_check_device_state,
+        .vhost_get_shmem_config = vhost_user_get_shmem_config,
 };
diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
index 70c2e8ffee..b40d82a111 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -159,6 +159,14 @@ typedef int (*vhost_set_device_state_fd_op)(struct vhost_dev *dev,
                                             int *reply_fd,
                                             Error **errp);
 typedef int (*vhost_check_device_state_op)(struct vhost_dev *dev, Error **errp);
+/*
+ * Max regions is VIRTIO_MAX_SHMEM_REGIONS, so that is the maximum
+ * number of memory_sizes that will be accepted. */
+typedef int (*vhost_get_shmem_config_op)(struct vhost_dev *dev,
+                                         int *nregions,
+                                         uint64_t *memory_sizes,
+                                         Error **errp);
+
 
 typedef struct VhostOps {
     VhostBackendType backend_type;
@@ -214,6 +222,7 @@ typedef struct VhostOps {
     vhost_supports_device_state_op vhost_supports_device_state;
     vhost_set_device_state_fd_op vhost_set_device_state_fd;
     vhost_check_device_state_op vhost_check_device_state;
+    vhost_get_shmem_config_op vhost_get_shmem_config;
 } VhostOps;
 
 int vhost_backend_update_device_iotlb(struct vhost_dev *dev,
diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
index 9a3f238b43..bacc7d184c 100644
--- a/include/hw/virtio/vhost-user.h
+++ b/include/hw/virtio/vhost-user.h
@@ -32,6 +32,7 @@ enum VhostUserProtocolFeature {
     /* Feature 17 reserved for VHOST_USER_PROTOCOL_F_XEN_MMAP. */
     VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 18,
     VHOST_USER_PROTOCOL_F_DEVICE_STATE = 19,
+    VHOST_USER_PROTOCOL_F_SHMEM = 20,
     VHOST_USER_PROTOCOL_F_MAX
 };
 
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index a778547c79..319e2f5b06 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -81,6 +81,8 @@ typedef struct VirtQueueElement
 
 #define VIRTIO_NO_VECTOR 0xffff
 
+#define VIRTIO_MAX_SHMEM_REGIONS 256
+
 /* special index value used internally for config irqs */
 #define VIRTIO_CONFIG_IRQ_IDX -1
 
-- 
2.48.1