alsa/NonBlock: throw on snd_pcm_poll_descriptors_revents() error

This function is sparsely documented and a look at the bluez-alsa source code shows that implementations make undocumented assumptions on the `struct pollfd` array parameter which can lead to strange effects.

alsa/NonBlock: throw on snd_pcm_poll_descriptors_revents() error
5cb60398 · Max Kellermann · 9c5790ab · 5cb60398 · 5cb60398
Commit 5cb60398 authored Dec 04, 2018 by Max Kellermann
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Showing with 8 additions and 3 deletions

NonBlock.cxx src/lib/alsa/NonBlock.cxx +5 -2

NonBlock.hxx src/lib/alsa/NonBlock.hxx +3 -1

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--- a/src/lib/alsa/NonBlock.cxx
+++ b/src/lib/alsa/NonBlock.cxx
@@ -50,7 +50,7 @@ AlsaNonBlockPcm::PrepareSockets(MultiSocketMonitor &m, snd_pcm_t *pcm)

 void
 AlsaNonBlockPcm::DispatchSockets(MultiSocketMonitor &m,
-				 snd_pcm_t *pcm) noexcept
+				 snd_pcm_t *pcm)
 {
 	int count = snd_pcm_poll_descriptors_count(pcm);
 	if (count <= 0)
@@ -69,7 +69,10 @@ AlsaNonBlockPcm::DispatchSockets(MultiSocketMonitor &m,
 		});

 	unsigned short dummy;
-	snd_pcm_poll_descriptors_revents(pcm, pfds, i - pfds, &dummy);
+	int err = snd_pcm_poll_descriptors_revents(pcm, pfds, i - pfds, &dummy);
+	if (err < 0)
+		throw FormatRuntimeError("snd_pcm_poll_descriptors_revents() failed: %s",
+					 snd_strerror(-err));
 }

 std::chrono::steady_clock::duration

--- a/src/lib/alsa/NonBlock.hxx
+++ b/src/lib/alsa/NonBlock.hxx
@@ -45,8 +45,10 @@ public:
 	/**
 	 * Wrapper for snd_pcm_poll_descriptors_revents(), to be
 	 * called from MultiSocketMonitor::DispatchSockets().
+	 *
+	 * Throws on error.
 	 */
-	void DispatchSockets(MultiSocketMonitor &m, snd_pcm_t *pcm) noexcept;
+	void DispatchSockets(MultiSocketMonitor &m, snd_pcm_t *pcm);
 };

 /**