Author: Ivan Krylov <krylov.r00t@gmail.com>
Date:   Sat May 4 11:59:58 2019 +0300

    Add ALSA volume support
    
    To use, add -DALSA to CPPFLAGS, -lasound to LDFLAGS and pass the
    control name (e.g. Master) as argument to vol_perc in config.h.

diff --git a/components/volume.c b/components/volume.c
index 6cec556..15c5a39 100644
--- a/components/volume.c
+++ b/components/volume.c
@@ -182,6 +182,61 @@
 
 		return bprintf("%d", value);
 	}
+#elif defined(ALSA)
+	#include <alsa/asoundlib.h>
+
+	static const char *devname = "default";
+	const char *
+	vol_perc(const char *mixname)
+	{
+		snd_mixer_t *mixer = NULL;
+		snd_mixer_selem_id_t *mixid = NULL;
+		snd_mixer_elem_t *elem = NULL;
+		long min = 0, max = 0, volume = -1;
+		int err;
+
+		if ((err = snd_mixer_open(&mixer, 0))) {
+			warn("snd_mixer_open: %d", err);
+			return NULL;
+		}
+		if ((err = snd_mixer_attach(mixer, devname))) {
+			warn("snd_mixer_attach(mixer, \"%s\"): %d", devname, err);
+			goto cleanup;
+		}
+		if ((err = snd_mixer_selem_register(mixer, NULL, NULL))) {
+			warn("snd_mixer_selem_register(mixer, NULL, NULL): %d", err);
+			goto cleanup;
+		}
+		if ((err = snd_mixer_load(mixer))) {
+			warn("snd_mixer_load(mixer): %d", err);
+			goto cleanup;
+		}
+
+		snd_mixer_selem_id_alloca(&mixid);
+		snd_mixer_selem_id_set_name(mixid, mixname);
+		snd_mixer_selem_id_set_index(mixid, 0);
+
+		elem = snd_mixer_find_selem(mixer, mixid);
+		if (!elem) {
+			warn("snd_mixer_find_selem(mixer, \"%s\") == NULL", mixname);
+			goto cleanup;
+		}
+
+		if ((err = snd_mixer_selem_get_playback_volume_range(elem, &min, &max))) {
+			warn("snd_mixer_selem_get_playback_volume_range(): %d", err);
+			goto cleanup;
+		}
+		if ((err = snd_mixer_selem_get_playback_volume(elem, SND_MIXER_SCHN_MONO, &volume))) {
+			warn("snd_mixer_selem_get_playback_volume(): %d", err);
+		}
+
+	cleanup:
+		snd_mixer_free(mixer);
+		snd_mixer_detach(mixer, devname);
+		snd_mixer_close(mixer);
+
+		return volume == -1 ? NULL : bprintf("%.0f", (volume-min)*100./(max-min));
+	}
 #else
 	#include <sys/soundcard.h>