[client] audio: handle USB transport backpressure

client/include/interface/usbredir.h

@@ -21,6 +21,8 @@
 #ifndef _H_LG_CLIENT_USBREDIR_INTERFACE_
 #define _H_LG_CLIENT_USBREDIR_INTERFACE_
 
+#include <stdbool.h>
+
 struct usbredirparser;
 
 typedef struct LG_USBRedirDeviceOps
@@ -31,9 +33,9 @@ typedef struct LG_USBRedirDeviceOps
   /* Queue the device descriptors and connection announcement. */
   void (*plug)(void * opaque, struct usbredirparser * parser);
 
-  /* Queue time-sensitive device data immediately before parser output is
-   * flushed. */
-  void (*process)(void * opaque);
+  /* Process device data immediately before parser output is flushed.
+   * writable is false while previously queued output is backpressured. */
+  void (*process)(void * opaque, bool writable);
 
   /* Stop all device activity. The bridge sends the disconnect packet. */
   void (*unplug)(void * opaque);

client/src/usb_audio.c

@@ -381,6 +381,7 @@ struct LG_USBAudio
   uint64_t                 feedbackNextPacketTime;
   uint32_t                 feedbackQueueTarget;
   atomic_uint              feedbackValue;
+  bool                     outputBackpressured;
 
   atomic_bool              recordStreaming;
   atomic_bool              recordAccepting;
@@ -924,6 +925,7 @@ static void resetDevice(LG_USBAudio * audio)
   audio->playbackSampleRate  = LG_USB_AUDIO_DEFAULT_SAMPLE_RATE;
   audio->recordBatchPackets  = 1;
   audio->recordSafetyPackets = 1;
+  audio->outputBackpressured = false;
   atomic_store_explicit(&audio->recordSampleRate,
       LG_USB_AUDIO_DEFAULT_SAMPLE_RATE, memory_order_relaxed);
   atomic_store_explicit(&audio->recordRateQ16,
@@ -1220,7 +1222,7 @@ static void sendRecordPacketBatch(LG_USBAudio * audio, uint32_t count,
 static void sendRecordRefill(LG_USBAudio * audio, uint64_t rateQ16)
 {
   const uint32_t count = min(
-      audio->recordRefillPackets, USB_AUDIO_RECORD_MAX_BATCH);
+      audio->recordRefillPackets, audio->recordBatchPackets);
   sendRecordPacketBatch(audio, count, rateQ16, true, 0, 0);
   audio->recordRefillPackets -= count;
   if (!audio->recordRefillPackets)
@@ -1277,7 +1279,7 @@ static void sendRecordPackets(LG_USBAudio * audio)
   }
 
   const uint32_t sendCount = (uint32_t)min(
-      count, (uint64_t)USB_AUDIO_RECORD_MAX_BATCH);
+      count, (uint64_t)audio->recordBatchPackets);
   const uint64_t catchupFrames =
     (audio->recordPacketPhase + rateQ16 * count) /
       USB_AUDIO_RECORD_RATE_DENOMINATOR;
@@ -1823,11 +1825,29 @@ static void reportPlaybackDebug(LG_USBAudio * audio)
   audio->playbackInvalidPackets   = 0;
 }
 
-static void processDevice(void * opaque)
+static void processDevice(void * opaque, bool writable)
 {
   LG_USBAudio * audio = opaque;
+  const uint64_t now = streamTime();
+  if (!writable)
+  {
+    if (atomic_load_explicit(
+          &audio->recordStreaming, memory_order_acquire))
+      audio->recordNextPacketTime =
+        now + USB_AUDIO_RECORD_PACKET_INTERVAL_NS;
+    audio->outputBackpressured = true;
+  }
+  else if (audio->outputBackpressured)
+  {
+    audio->recordNextPacketTime =
+      now + USB_AUDIO_RECORD_PACKET_INTERVAL_NS;
+    audio->outputBackpressured = false;
+  }
+
+  if (writable)
     sendFeedbackPacketsDue(audio);
   flushPlayback(audio);
+  if (writable)
     sendRecordPackets(audio);
   reportPlaybackDebug(audio);
   reportRecordDebug(audio);
@@ -1986,6 +2006,9 @@ uint64_t lgUsbAudio_processDelayNs(const LG_USBAudio * audio)
   if (!audio)
     return UINT64_MAX;
 
+  if (audio->outputBackpressured)
+    return UINT64_MAX;
+
   const uint64_t now = streamTime();
   uint64_t delay = UINT64_MAX;
 

client/transports/SPICE/session.c

@@ -376,6 +376,11 @@ int spiceSession_thread(void * opaque)
       while (lgUsbRedir_disconnectPending(transport->usbRedir) &&
           microtime() < deadline)
       {
+        if (!lgUsbRedir_process(transport->usbRedir))
+        {
+          DEBUG_WARN("Failed to process USB audio device removal");
+          break;
+        }
         status = purespice_process(10);
         if (status != PS_STATUS_RUN)
           break;

client/transports/SPICE/usbredir.c

@@ -83,11 +83,12 @@ static int readUSBRedir(void * opaque, uint8_t * data, int count)
 static int writeUSBRedir(void * opaque, uint8_t * data, int count)
 {
   LG_USBRedir * usbredir = opaque;
-  if (!usbredir->channel ||
-      !purespice_usbRedirWrite(usbredir->channel, data, count))
+  if (!usbredir->channel)
     return -1;
 
-  return count;
+  const ssize_t written = purespice_usbRedirWriteNonblocking(
+      usbredir->channel, data, count);
+  return written >= 0 && written <= count ? (int)written : -1;
 }
 
 static void logUSBRedir(void * opaque, int level, const char * message)
@@ -324,6 +325,14 @@ static bool processUSBRedir(LG_USBRedir * usbredir, bool recover)
     return result;
   }
 
+  bool result = flushUSBRedir(usbredir);
+  if (!result)
+  {
+    if (recover)
+      resetChannel(usbredir);
+    return false;
+  }
+
   if (usbredir->disconnectPending)
   {
     if (usbredir->disconnectDeadline &&
@@ -334,10 +343,7 @@ static bool processUSBRedir(LG_USBRedir * usbredir, bool recover)
       return true;
     }
 
-    const bool result = flushUSBRedir(usbredir);
-    if (!result && recover)
-      resetChannel(usbredir);
-    return result;
+    return true;
   }
 
   const bool desired = atomic_load_explicit(&usbredir->desiredPlugged,
@@ -359,12 +365,25 @@ static bool processUSBRedir(LG_USBRedir * usbredir, bool recover)
         now + USB_REDIR_DISCONNECT_TIMEOUT_NS : 0;
       usbredirparser_send_device_disconnect(usbredir->parser);
     }
+
+    result = flushUSBRedir(usbredir);
+    if (!result)
+    {
+      if (recover)
+        resetChannel(usbredir);
+      return false;
+    }
   }
 
   if (usbredir->plugged && usbredir->deviceOps->process)
-    usbredir->deviceOps->process(usbredir->deviceOpaque);
+  {
+    const bool writable =
+      usbredirparser_has_data_to_write(usbredir->parser) == 0 &&
+      purespice_usbRedirWritable(usbredir->channel);
+    usbredir->deviceOps->process(usbredir->deviceOpaque, writable);
+  }
 
-  const bool result = flushUSBRedir(usbredir);
+  result = flushUSBRedir(usbredir);
   if (!result && recover)
     resetChannel(usbredir);
   return result;