QXL interface: add a function to identify monitors in the guest

Adds a function to let QEMU provide information to identify graphics
devices and their monitors in the guest. The function
(spice_qxl_set_device_info) sets the device address (e.g. a PCI path)
and monitor ID -> device display ID mapping of displays exposed by given
QXL interface.

Signed-off-by: Lukáš Hrázký <lhrazky@redhat.com>
Acked-by: Jonathon Jongsma <jjongsma@redhat.com>

server/red-qxl.c

@@ -41,6 +41,9 @@
 #include "red-qxl.h"
 
 
+#define MAX_DEVICE_ADDRESS_LEN 256
+#define MAX_MONITORS_COUNT 16
+
 struct QXLState {
     QXLWorker qxl_worker;
     QXLInstance *qxl;
@@ -53,6 +56,9 @@ struct QXLState {
     unsigned int max_monitors;
     RedsState *reds;
     RedWorker *worker;
+    char device_address[MAX_DEVICE_ADDRESS_LEN];
+    uint32_t device_display_ids[MAX_MONITORS_COUNT];
+    size_t monitors_count;  // length of ^^^
 
     pthread_mutex_t scanout_mutex;
     SpiceMsgDisplayGlScanoutUnix scanout;
@@ -846,6 +852,44 @@ void red_qxl_gl_draw_async_complete(QXLInstance *qxl)
     red_qxl_async_complete(qxl, cookie);
 }
 
+SPICE_GNUC_VISIBLE
+void spice_qxl_set_device_info(QXLInstance *instance,
+                               const char *device_address,
+                               uint32_t device_display_id_start,
+                               uint32_t device_display_id_count)
+{
+    g_return_if_fail(device_address != NULL);
+
+    size_t da_len = strnlen(device_address, MAX_DEVICE_ADDRESS_LEN);
+    if (da_len >= MAX_DEVICE_ADDRESS_LEN) {
+        spice_error("Device address too long: %lu > %u", da_len, MAX_DEVICE_ADDRESS_LEN);
+        return;
+    }
+
+    if (device_display_id_count > MAX_MONITORS_COUNT) {
+        spice_error("Device display ID count (%u) is greater than limit %u",
+                    device_display_id_count,
+                    MAX_MONITORS_COUNT);
+        return;
+    }
+
+    g_strlcpy(instance->st->device_address, device_address, MAX_DEVICE_ADDRESS_LEN);
+
+    g_debug("QXL Instance %d setting device address \"%s\" and monitor -> device display mapping:",
+            instance->id,
+            device_address);
+
+    // store the mapping monitor_id -> device_display_id
+    for (uint32_t monitor_id = 0; monitor_id < device_display_id_count; ++monitor_id) {
+        uint32_t device_display_id = device_display_id_start + monitor_id;
+        instance->st->device_display_ids[monitor_id] = device_display_id;
+        g_debug("   monitor ID %u -> device display ID %u",
+                monitor_id, device_display_id);
+    }
+
+    instance->st->monitors_count = device_display_id_count;
+}
+
 void red_qxl_init(RedsState *reds, QXLInstance *qxl)
 {
     QXLState *qxl_state;

server/spice-qxl.h

@@ -115,6 +115,52 @@ void spice_qxl_gl_draw_async(QXLInstance *instance,
                              uint32_t w, uint32_t h,
                              uint64_t cookie);
 
+/* since spice 0.14.2 */
+
+/**
+ * spice_qxl_set_device_info:
+ * @instance the QXL instance to set the path to
+ * @device_address the path of the device this QXL instance belongs to
+ * @device_display_id_start the starting device display ID of this interface,
+ *                          i.e. the one monitor ID 0 maps to
+ * @device_display_id_count the total number of device display IDs on this
+ *                          interface
+ *
+ * Sets the device information for this QXL interface, i.e. the hardware
+ * address (e.g. PCI) of the graphics device and the IDs of the displays of the
+ * graphics device that are exposed by this interface (device display IDs).
+ *
+ * The supported device address format is:
+ * "pci/<DOMAIN>/<SLOT>.<FUNCTION>/.../<SLOT>.<FUNCTION>"
+ *
+ * The "pci" identifies the rest of the string as a PCI address. It is the only
+ * supported address at the moment, other identifiers can be introduced later.
+ * <DOMAIN> is the PCI domain, followed by <SLOT>.<FUNCTION> of any PCI bridges
+ * in the chain leading to the device. The last <SLOT>.<FUNCTION> is the
+ * graphics device. All of <DOMAIN>, <SLOT>, <FUNCTION> are hexadecimal numbers
+ * with the following number of digits:
+ *   <DOMAIN>: 4
+ *   <SLOT>: 2
+ *   <FUNCTION>: 1
+ *
+ * The device_display_id_{start,count} denotes the sequence of device display
+ * IDs that map to the zero-based sequence of monitor IDs provided by monitors
+ * config on this interface. For example with device_display_id_start = 2 and
+ * device_display_id_count = 3 you get the following mapping:
+ * monitor_id  ->  device_display_id
+ *          0  ->  2
+ *          1  ->  3
+ *          2  ->  4
+ *
+ * Note this example is unsupported in practice. The only supported cases are
+ * either a single device display ID (count = 1) or multiple device display IDs
+ * in a sequence starting from 0.
+ */
+void spice_qxl_set_device_info(QXLInstance *instance,
+                               const char *device_address,
+                               uint32_t device_display_id_start,
+                               uint32_t device_display_id_count);
+
 typedef struct QXLDevInitInfo {
     uint32_t num_memslots_groups;
     uint32_t num_memslots;

server/spice-server.syms

@@ -173,3 +173,8 @@ SPICE_SERVER_0.13.2 {
 global:
     spice_server_set_video_codecs;
 } SPICE_SERVER_0.13.1;
+
+SPICE_SERVER_0.14.2 {
+global:
+    spice_qxl_set_device_info;
+} SPICE_SERVER_0.13.2;