vfio-user: implement message send infrastructure

Add plumbing for sending vfio-user messages on the control socket.
Add initial version negotation on connection.

Originally-by: John Johnson <john.g.johnson@oracle.com>
Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250625193012.2316242-5-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio-user/pci.c

@@ -20,6 +20,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(VFIOUserPCIDevice, VFIO_USER_PCI)
 struct VFIOUserPCIDevice {
     VFIOPCIDevice device;
     SocketAddress *socket;
+    bool send_queued;   /* all sends are queued */
 };
 
 /*
@@ -92,6 +93,16 @@ static void vfio_user_pci_realize(PCIDevice *pdev, Error **errp)
     vbasedev->proxy = proxy;
     vfio_user_set_handler(vbasedev, vfio_user_pci_process_req, vdev);
 
+    vbasedev->name = g_strdup_printf("vfio-user:%s", sock_name);
+
+    if (udev->send_queued) {
+        proxy->flags |= VFIO_PROXY_FORCE_QUEUED;
+    }
+
+    if (!vfio_user_validate_version(proxy, errp)) {
+        goto error;
+    }
+
     /*
      * vfio-user devices are effectively mdevs (don't use a host iommu).
      */
@@ -101,9 +112,13 @@ static void vfio_user_pci_realize(PCIDevice *pdev, Error **errp)
     if (!vfio_device_attach_by_iommu_type(TYPE_VFIO_IOMMU_USER,
                                           vbasedev->name, vbasedev,
                                           as, errp)) {
-        error_prepend(errp, VFIO_MSG_PREFIX, vbasedev->name);
-        return;
+        goto error;
     }
+
+    return;
+
+error:
+    error_prepend(errp, VFIO_MSG_PREFIX, vdev->vbasedev.name);
 }
 
 static void vfio_user_instance_init(Object *obj)
@@ -153,6 +168,7 @@ static const Property vfio_user_pci_dev_properties[] = {
                        sub_vendor_id, PCI_ANY_ID),
     DEFINE_PROP_UINT32("x-pci-sub-device-id", VFIOPCIDevice,
                        sub_device_id, PCI_ANY_ID),
+    DEFINE_PROP_BOOL("x-send-queued", VFIOUserPCIDevice, send_queued, false),
 };
 
 static void vfio_user_pci_set_socket(Object *obj, Visitor *v, const char *name,

hw/vfio-user/protocol.h

@@ -50,4 +50,66 @@ enum vfio_user_command {
 #define VFIO_USER_NO_REPLY      0x10
 #define VFIO_USER_ERROR         0x20
 
+
+/*
+ * VFIO_USER_VERSION
+ */
+typedef struct {
+    VFIOUserHdr hdr;
+    uint16_t major;
+    uint16_t minor;
+    char capabilities[];
+} VFIOUserVersion;
+
+#define VFIO_USER_MAJOR_VER     0
+#define VFIO_USER_MINOR_VER     0
+
+#define VFIO_USER_CAP           "capabilities"
+
+/* "capabilities" members */
+#define VFIO_USER_CAP_MAX_FDS   "max_msg_fds"
+#define VFIO_USER_CAP_MAX_XFER  "max_data_xfer_size"
+#define VFIO_USER_CAP_PGSIZES   "pgsizes"
+#define VFIO_USER_CAP_MAP_MAX   "max_dma_maps"
+#define VFIO_USER_CAP_MIGR      "migration"
+
+/* "migration" members */
+#define VFIO_USER_CAP_PGSIZE            "pgsize"
+#define VFIO_USER_CAP_MAX_BITMAP        "max_bitmap_size"
+
+/*
+ * Max FDs mainly comes into play when a device supports multiple interrupts
+ * where each ones uses an eventfd to inject it into the guest.
+ * It is clamped by the the number of FDs the qio channel supports in a
+ * single message.
+ */
+#define VFIO_USER_DEF_MAX_FDS   8
+#define VFIO_USER_MAX_MAX_FDS   16
+
+/*
+ * Max transfer limits the amount of data in region and DMA messages.
+ * Region R/W will be very small (limited by how much a single instruction
+ * can process) so just use a reasonable limit here.
+ */
+#define VFIO_USER_DEF_MAX_XFER  (1024 * 1024)
+#define VFIO_USER_MAX_MAX_XFER  (64 * 1024 * 1024)
+
+/*
+ * Default pagesizes supported is 4k.
+ */
+#define VFIO_USER_DEF_PGSIZE    4096
+
+/*
+ * Default max number of DMA mappings is stolen from the
+ * linux kernel "dma_entry_limit"
+ */
+#define VFIO_USER_DEF_MAP_MAX   65535
+
+/*
+ * Default max bitmap size is also take from the linux kernel,
+ * where usage of signed ints limits the VA range to 2^31 bytes.
+ * Dividing that by the number of bits per byte yields 256MB
+ */
+#define VFIO_USER_DEF_MAX_BITMAP (256 * 1024 * 1024)
+
 #endif /* VFIO_USER_PROTOCOL_H */

hw/vfio-user/proxy.h

@@ -37,6 +37,7 @@ typedef struct VFIOUserMsg {
     uint32_t id;
     QemuCond cv;
     bool complete;
+    bool pending;
     enum msg_type type;
 } VFIOUserMsg;
 
@@ -56,6 +57,12 @@ typedef struct VFIOUserProxy {
     struct QIOChannel *ioc;
     void (*request)(void *opaque, VFIOUserMsg *msg);
     void *req_arg;
+    uint64_t max_xfer_size;
+    uint64_t max_send_fds;
+    uint64_t max_dma;
+    uint64_t dma_pgsizes;
+    uint64_t max_bitmap;
+    uint64_t migr_pgsize;
     int flags;
     QemuCond close_cv;
     AioContext *ctx;
@@ -78,6 +85,7 @@ typedef struct VFIOUserProxy {
 
 /* VFIOProxy flags */
 #define VFIO_PROXY_CLIENT        0x1
+#define VFIO_PROXY_FORCE_QUEUED  0x4
 
 typedef struct VFIODevice VFIODevice;
 
@@ -86,5 +94,6 @@ void vfio_user_disconnect(VFIOUserProxy *proxy);
 void vfio_user_set_handler(VFIODevice *vbasedev,
                            void (*handler)(void *opaque, VFIOUserMsg *msg),
                            void *reqarg);
+bool vfio_user_validate_version(VFIOUserProxy *proxy, Error **errp);
 
 #endif /* VFIO_USER_PROXY_H */

hw/vfio-user/trace-events

@@ -6,3 +6,5 @@
 vfio_user_recv_hdr(const char *name, uint16_t id, uint16_t cmd, uint32_t size, uint32_t flags) " (%s) id 0x%x cmd 0x%x size 0x%x flags 0x%x"
 vfio_user_recv_read(uint16_t id, int read) " id 0x%x read 0x%x"
 vfio_user_recv_request(uint16_t cmd) " command 0x%x"
+vfio_user_send_write(uint16_t id, int wrote) " id 0x%x wrote 0x%x"
+vfio_user_version(uint16_t major, uint16_t minor, const char *caps) " major %d minor %d caps: %s"