vbox6: don't call blocking 'read()' to start audio recording

Fixes #4580

repos/ports/ports/virtualbox6.hash

@@ -1 +1 @@
-db7d6d9b9ab32c34fcfb371dfc9e100b208ee982
+b59f4f8ca00b96a40a93f736676f5b4e830cbd01

repos/ports/src/virtualbox6/patches/audio.patch

@@ -0,0 +1,27 @@
+diff --git a/src/virtualbox6/src/VBox/Devices/Audio/DrvHostAudioOss.cpp b/src/virtualbox6/src/VBox/Devices/Audio/DrvHostAudioOss.cpp
+index d67f2bb..ea99bee 100644
+--- a/src/virtualbox6/src/VBox/Devices/Audio/DrvHostAudioOss.cpp
++++ b/src/virtualbox6/src/VBox/Devices/Audio/DrvHostAudioOss.cpp
+@@ -836,6 +836,13 @@ static DECLCALLBACK(uint32_t) drvHstAudOssHA_StreamGetReadable(PPDMIHOSTAUDIO pI
+         AssertMsgStmt(cbRet <= cbBuf, ("fragsize*fragments: %d, cbBuf=%#x\n", cbRet, cbBuf), 0);
+     }
+
++    /*
++     * On Genode the 'SNDCTL_DSP_SETTRIGGER' command should have started
++     * the recording. If no recording data arrives because of some error
++     * on the path (for example a crashed driver), the 'read()' call in
++     * the following section would block the VM, which is not desired.
++     */
++#if 0
+     /*
+      * HACK ALERT! To force the stream to start recording, we read a frame
+      *             here if we get back that there are zero bytes available
+@@ -854,7 +861,7 @@ static DECLCALLBACK(uint32_t) drvHstAudOssHA_StreamGetReadable(PPDMIHOSTAUDIO pI
+         RT_NOREF(cbRead);
+         LogFunc(("Dummy read for '%s' returns %zd (errno=%d)\n", pStreamOSS->Cfg.szName, cbRead, errno));
+     }
+-
++#endif
+     Log4Func(("returns %#x (%u) [cbBuf=%#x]\n", cbRet, cbRet, cbBuf));
+     return cbRet;
+ }

repos/ports/src/virtualbox6/patches/series

@@ -9,3 +9,4 @@ rttimer.patch
 devsvga.patch
 shaderlib.patch
 svga.patch
+audio.patch