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>

1 files changed, 62 insertions, 0 deletions

diff --git a/hw/vfio-user/protocol.h b/hw/vfio-user/protocol.h
index 4ddfb5f222..2d52d0fb10 100644
--- a/hw/vfio-user/protocol.h
+++ b/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 */