cubeb_oss: Fix for buffer overrun.

The hardware buffer is typically bigger than the software buffer.
Make sure to properly limit the available buffer size values
obtained from the DSP device.

While at it ensure to retry-polling in case either recording or
playback cannot move any data.

src/cubeb_oss.c

@@ -790,8 +790,8 @@ oss_wait_fds_for_space(cubeb_stream * s, long * nfrp)
 {
   audio_buf_info bi;
   struct pollfd pfds[2];
-  long nfr = LONG_MAX, tnfr;
-  int i = 0;
+  long nfr, tnfr;
+  int i;
 
   assert(s->play.fd != -1 || s->record.fd != -1);
   pfds[0].events = POLLOUT | POLLHUP;
@@ -801,6 +801,9 @@ oss_wait_fds_for_space(cubeb_stream * s, long * nfrp)
   pfds[1].revents = 0;
   pfds[1].fd = s->record.fd;
 
+retry:
+  nfr = LONG_MAX;
+
   if (poll(pfds, 2, 1000) == -1) {
     return CUBEB_ERROR;
   }
@@ -816,6 +819,15 @@ oss_wait_fds_for_space(cubeb_stream * s, long * nfrp)
       return CUBEB_STATE_ERROR;
     }
     tnfr = bi.bytes / s->play.frame_size;
+    if (tnfr <= 0) {
+      /* too little space - stop polling record, if any */
+      pfds[0].fd = s->play.fd;
+      pfds[1].fd = -1;
+      goto retry;
+    } else if (tnfr > (long)s->play.bufframes) {
+      /* too many frames available - limit */
+      tnfr = (long)s->play.bufframes;
+    }
     if (nfr > tnfr) {
       nfr = tnfr;
     }
@@ -825,6 +837,15 @@ oss_wait_fds_for_space(cubeb_stream * s, long * nfrp)
       return CUBEB_STATE_ERROR;
     }
     tnfr = bi.bytes / s->record.frame_size;
+    if (tnfr <= 0) {
+      /* too little space - stop polling playback, if any */
+      pfds[0].fd = -1;
+      pfds[1].fd = s->record.fd;
+      goto retry;
+    } else if (tnfr > (long)s->record.bufframes) {
+      /* too many frames available - limit */
+      tnfr = (long)s->record.bufframes;
+    }
     if (nfr > tnfr) {
       nfr = tnfr;
     }