output/alsa: add attributes "dop" and "allowed_formats"

NEWS

@@ -12,6 +12,7 @@ ver 0.21 (not yet released)
   - pcm: support audio/L24 (RFC 3190)
 * output
   - alsa: non-blocking mode
+  - alsa: change "dop" and "allowed_formats" settings at runtime
   - shout: support the Shine encoder plugin
   - sndio: remove support for the broken RoarAudio sndio emulation
 * mixer

doc/user.xml

@@ -3539,6 +3539,52 @@ run</programlisting>
             </tbody>
           </tgroup>
         </informaltable>
+
+        <para>
+          The following attributes can be configured at runtime using
+          the <command>outputset</command> command:
+        </para>
+
+        <informaltable>
+          <tgroup cols="2">
+            <thead>
+              <row>
+                <entry>Setting</entry>
+                <entry>Description</entry>
+              </row>
+            </thead>
+            <tbody>
+              <row>
+                <entry>
+                  <varname>dop</varname>
+                  <parameter>1|0</parameter>
+                </entry>
+                <entry>
+                  <para>
+                    Allows changing the <varname>dop</varname>
+                    configuration setting at runtime.  This takes
+                    effect the next time the output is opened.
+                  </para>
+                </entry>
+              </row>
+
+              <row>
+                <entry>
+                  <varname>allowed_formats</varname>
+                  <parameter>F1 F2 ...</parameter>
+                </entry>
+                <entry>
+                  <para>
+                    Allows changing the
+                    <varname>allowed_formats</varname> configuration
+                    setting at runtime.  This takes effect the next
+                    time the output is opened.
+                  </para>
+                </entry>
+              </row>
+            </tbody>
+          </tgroup>
+        </informaltable>
       </section>
 
       <section>

src/lib/alsa/AllowedFormat.cxx

@@ -21,6 +21,7 @@
 #include "AllowedFormat.hxx"
 #include "AudioParser.hxx"
 #include "util/IterableSplitString.hxx"
+#include "util/StringBuffer.hxx"
 
 #include <stdexcept>
 
@@ -65,4 +66,24 @@ AllowedFormat::ParseList(StringView s)
 	return list;
 }
 
+std::string
+ToString(const std::forward_list<AllowedFormat> &allowed_formats) noexcept
+{
+	std::string result;
+
+	for (const auto &i : allowed_formats) {
+		if (!result.empty())
+			result.push_back(' ');
+
+		result += ::ToString(i.format);
+
+#ifdef ENABLE_DSD
+		if (i.dop)
+			result += "=dop";
+#endif
+	}
+
+	return result;
+}
+
 } // namespace Alsa

src/lib/alsa/AllowedFormat.hxx

@@ -24,6 +24,7 @@
 #include "AudioFormat.hxx"
 
 #include <forward_list>
+#include <string>
 
 struct StringView;
 
@@ -54,6 +55,9 @@ struct AllowedFormat {
 	static std::forward_list<AllowedFormat> ParseList(StringView s);
 };
 
+std::string
+ToString(const std::forward_list<AllowedFormat> &allowed_formats) noexcept;
+
 } // namespace Alsa
 
 #endif

src/output/plugins/AlsaOutputPlugin.cxx

@@ -69,7 +69,7 @@ class AlsaOutput final
 	 *
 	 * @see http://dsd-guide.com/dop-open-standard
 	 */
-	const bool dop_setting;
+	bool dop_setting;
 #endif
 
 	/** libasound's buffer_time setting (in microseconds) */
@@ -83,6 +83,11 @@ class AlsaOutput final
 
 	std::forward_list<Alsa::AllowedFormat> allowed_formats;
 
+	/**
+	 * Protects #dop_setting and #allowed_formats.
+	 */
+	mutable Mutex attributes_mutex;
+
 	/** the libasound PCM device handle */
 	snd_pcm_t *pcm;
 
@@ -186,6 +191,9 @@ public:
 	}
 
 private:
+	const std::map<std::string, std::string> GetAttributes() const noexcept override;
+	void SetAttribute(std::string &&name, std::string &&value) override;
+
 	void Enable() override;
 	void Disable() noexcept override;
 
@@ -348,6 +356,40 @@ AlsaOutput::AlsaOutput(EventLoop &_loop, const ConfigBlock &block)
 		allowed_formats = Alsa::AllowedFormat::ParseList(allowed_formats_string);
 }
 
+const std::map<std::string, std::string>
+AlsaOutput::GetAttributes() const noexcept
+{
+	const std::lock_guard<Mutex> lock(attributes_mutex);
+
+	return {
+		std::make_pair("allowed_formats",
+			       Alsa::ToString(allowed_formats)),
+#ifdef ENABLE_DSD
+		std::make_pair("dop", dop_setting ? "1" : "0"),
+#endif
+	};
+}
+
+void
+AlsaOutput::SetAttribute(std::string &&name, std::string &&value)
+{
+	if (name == "allowed_formats") {
+		const std::lock_guard<Mutex> lock(attributes_mutex);
+		allowed_formats = Alsa::AllowedFormat::ParseList({value.data(), value.length()});
+#ifdef ENABLE_DSD
+	} else if (name == "dop") {
+		const std::lock_guard<Mutex> lock(attributes_mutex);
+		if (value == "0")
+			dop_setting = false;
+		else if (value == "1")
+			dop_setting = true;
+		else
+			throw std::invalid_argument("Bad 'dop' value");
+#endif
+	} else
+		AudioOutput::SetAttribute(std::move(name), std::move(value));
+}
+
 void
 AlsaOutput::Enable()
 {
@@ -548,15 +590,23 @@ void
 AlsaOutput::Open(AudioFormat &audio_format)
 {
 #ifdef ENABLE_DSD
-	bool dop = dop_setting;
+	bool dop;
 #endif
 
-	if (!allowed_formats.empty()) {
-		const auto &a = BestMatch(allowed_formats, audio_format);
-		audio_format.ApplyMask(a.format);
+	{
+		const std::lock_guard<Mutex> lock(attributes_mutex);
 #ifdef ENABLE_DSD
-		dop = a.dop;
+		dop = dop_setting;
 #endif
+
+		if (!allowed_formats.empty()) {
+			const auto &a = BestMatch(allowed_formats,
+						  audio_format);
+			audio_format.ApplyMask(a.format);
+#ifdef ENABLE_DSD
+			dop = a.dop;
+#endif
+		}
 	}
 
 	int err = snd_pcm_open(&pcm, GetDevice(),