output/alsa: remove option "use_mmap"

MPD does not really take advantage of memory-mapped I/O by generating
data right into the ALSA buffer; using plain snd_pcm_mmap_writei() has
no advantage compared to snd_pcm_writei().  Let's kill this
non-feature.

NEWS

@@ -29,6 +29,7 @@ ver 0.20 (not yet released)
   - flac: new plugin which reads the "CUESHEET" metadata block
 * output
   - alsa: fix multi-channel order
+  - alsa: remove option "use_mmap"
   - jack: reduce CPU usage
   - pulse: set channel map to WAVE-EX
   - recorder: record tags

doc/mpd.conf.5

@@ -238,11 +238,6 @@ probably only useful if your alsa device has more than one
 identically\-named mixer control.  The default is "0".  Use "amixer
 scontrols" to see the list of controls with their indexes.
 .TP
-.B use_mmap <yes or no>
-Setting this allows you to use memory-mapped I/O.  Certain hardware setups may
-benefit from this, but most do not.  Most users do not need to set this.  The
-default is to not use memory-mapped I/O.
-.TP
 .B auto_resample <yes or no>
 Setting this to "no" disables ALSA's software resampling, if the
 hardware does not support a specific sample rate.  This lets MPD do

doc/user.xml

@@ -2482,17 +2482,6 @@ buffer_size: 16384</programlisting>
                   ...).
                 </entry>
               </row>
-              <row>
-                <entry>
-                  <varname>use_mmap</varname>
-                  <parameter>yes|no</parameter>
-                </entry>
-                <entry>
-                  If set to <parameter>yes</parameter>, then
-                  <filename>libasound</filename> will try to use
-                  memory mapped I/O.
-                </entry>
-              </row>
               <row>
                 <entry>
                   <varname>buffer_time</varname>

src/output/plugins/AlsaOutputPlugin.cxx

@@ -50,9 +50,6 @@ static constexpr unsigned MPD_ALSA_BUFFER_TIME_US = 500000;
 
 static constexpr unsigned MPD_ALSA_RETRY_NR = 5;
 
-typedef snd_pcm_sframes_t alsa_writei_t(snd_pcm_t * pcm, const void *buffer,
-					snd_pcm_uframes_t size);
-
 struct AlsaOutput {
 	AudioOutput base;
 
@@ -64,9 +61,6 @@ struct AlsaOutput {
 	 */
 	std::string device;
 
-	/** use memory mapped I/O? */
-	bool use_mmap;
-
 #ifdef ENABLE_DSD
 	/**
 	 * Enable DSD over PCM according to the DoP standard standard?
@@ -88,13 +82,6 @@ struct AlsaOutput {
 	/** the libasound PCM device handle */
 	snd_pcm_t *pcm;
 
-	/**
-	 * a pointer to the libasound writei() function, which is
-	 * snd_pcm_writei() or snd_pcm_mmap_writei(), depending on the
-	 * use_mmap configuration
-	 */
-	alsa_writei_t *writei;
-
 	/**
 	 * The size of one audio frame passed to method play().
 	 */
@@ -136,7 +123,7 @@ struct AlsaOutput {
 
 	AlsaOutput()
 		:base(alsa_output_plugin),
-		 mode(0), writei(snd_pcm_writei) {
+		 mode(0) {
 	}
 
 	~AlsaOutput() {
@@ -177,7 +164,7 @@ private:
 	 * Write silence to the ALSA device.
 	 */
 	void WriteSilence(snd_pcm_uframes_t nframes) {
-		writei(pcm, silence, nframes);
+		snd_pcm_writei(pcm, silence, nframes);
 	}
 
 };
@@ -192,8 +179,6 @@ AlsaOutput::Configure(const ConfigBlock &block, Error &error)
 
 	device = block.GetBlockValue("device", "");
 
-	use_mmap = block.GetBlockValue("use_mmap", false);
-
 #ifdef ENABLE_DSD
 	dop = block.GetBlockValue("dop", false) ||
 		/* legacy name from MPD 0.18 and older: */
@@ -488,28 +473,11 @@ configure_hw:
 	if (err < 0)
 		goto error;
 
-	if (ad->use_mmap) {
-		err = snd_pcm_hw_params_set_access(ad->pcm, hwparams,
-						   SND_PCM_ACCESS_MMAP_INTERLEAVED);
-		if (err < 0) {
-			FormatWarning(alsa_output_domain,
-				      "Cannot set mmap'ed mode on ALSA device \"%s\": %s",
-				      ad->GetDevice(), snd_strerror(-err));
-			LogWarning(alsa_output_domain,
-				   "Falling back to direct write mode");
-			ad->use_mmap = false;
-		} else
-			ad->writei = snd_pcm_mmap_writei;
-	}
-
-	if (!ad->use_mmap) {
-		cmd = "snd_pcm_hw_params_set_access";
-		err = snd_pcm_hw_params_set_access(ad->pcm, hwparams,
-						   SND_PCM_ACCESS_RW_INTERLEAVED);
-		if (err < 0)
-			goto error;
-		ad->writei = snd_pcm_writei;
-	}
+	cmd = "snd_pcm_hw_params_set_access";
+	err = snd_pcm_hw_params_set_access(ad->pcm, hwparams,
+					   SND_PCM_ACCESS_RW_INTERLEAVED);
+	if (err < 0)
+		goto error;
 
 	err = alsa_output_setup_format(ad->pcm, hwparams, audio_format,
 				       params);
@@ -890,7 +858,7 @@ AlsaOutput::Play(const void *chunk, size_t size, Error &error)
 	assert(size > 0);
 
 	while (true) {
-		snd_pcm_sframes_t ret = writei(pcm, chunk, size);
+		snd_pcm_sframes_t ret = snd_pcm_writei(pcm, chunk, size);
 		if (ret > 0) {
 			period_position = (period_position + ret)
 				% period_frames;