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mixfs: add "volume" file with "mix" control to set the output volume of the mixed inputs

--- a/sys/man/1/audio

+++ b/sys/man/1/audio

@@ -346,8 +346,13 @@

 .B /mnt/mix

 and then binds

 .B /mnt/mix/audio

+and

+.B /mnt/mix/volume

 over

 .BR /dev .

+.B /dev/volume

+from the parent namespace is proxied with an additional control "mix"

+which is used to set the output volume of the mixer.

 A alternative mountpoint 

 .I mtpt

 can be specified with the

--- a/sys/src/cmd/audio/mixfs/mixfs.c

+++ b/sys/src/cmd/audio/mixfs/mixfs.c

@@ -11,6 +11,9 @@

 	FREQ = 44100,

 };

+#define MIN(a,b) ((a)<(b)?(a):(b))

+#define MAX(a,b) ((a)>(b)?(a):(b))

+

 typedef struct Stream Stream;

 struct Stream

 {

@@ -33,6 +36,10 @@

 Stream	streams[16];

+int	volfd;

+int	volume[2] = {100, 100};

+int	vol64k[2] = {65536, 65536};

+

 int

 s16(uchar *p)

 {

@@ -101,10 +108,9 @@

 {

 	Stream *s;

-	if(f->file != nil && strcmp(f->file->name, "audio") == 0 && (s = f->aux) != nil){

-		f->aux = nil;

+	if(f->file != nil && strcmp(f->file->name, "audio") == 0 && (s = f->aux) != nil)

 		s->used = 0;

-	}

+	f->aux = nil;

 }

 void

@@ -179,7 +185,7 @@

 		rp = mixrp;

 		for(i=0; i<m; i++){

 			for(j=0; j<NCHAN; j++){

-				v = clip16(mixbuf[rp % NBUF][j]);

+				v = clip16(mixbuf[rp % NBUF][j])*vol64k[j] / 65536;

 				lbbuf[rp % NBUF][j] = v;

 				mixbuf[rp % NBUF][j] = 0;

 				*p++ = v & 0xFF;

@@ -205,6 +211,18 @@

 	Stream *s;

 	uchar *p;

+	if(r->fid->file->aux == &volfd){

+		static char svol[4096];

+		if(r->ifcall.offset == 0){

+			m = snprint(svol, sizeof(svol), "mix %d %d\n", volume[0], volume[1]);

+			if((n = pread(volfd, svol+m, sizeof(svol)-m-1, 0)) > 0)

+				svol[m+n] = 0;

+		}

+		readstr(r, svol);

+		respond(r, nil);

+		return;

+	}

+

 	p = (uchar*)r->ofcall.data;

 	n = r->ifcall.count;

 	n &= ~(NCHAN*2 - 1);

@@ -260,6 +278,39 @@

 	Stream *s;

 	uchar *p;

+	if(r->fid->file->aux == &volfd){

+		char msg[64], *f[5];

+		int x[2], nf;

+

+		r->ofcall.count = r->ifcall.count;

+		snprint(msg, sizeof(msg), "%.*s",

+			utfnlen((char*)r->ifcall.data, r->ifcall.count), (char*)r->ifcall.data);

+		nf = tokenize(msg, f, nelem(f));

+		if(nf > 1 && strcmp(f[0], "mix") == 0){

+			x[0] = atoi(f[1]);

+			x[1] = nf < 3 ? x[0] : atoi(f[2]);

+			if(f[1][0] == '+' || f[1][0] == '-'){

+				x[0] += volume[0];

+				x[1] += volume[1];

+			}

+			volume[0] = MIN(MAX(0, x[0]), 100);

+			volume[1] = MIN(MAX(0, x[1]), 100);

+			/* ≈60dB dynamic range; [0-100] → [0-65536] */

+			vol64k[0] = 65.536 * (exp(volume[0] * 0.0690876) - 1.0);

+			vol64k[1] = 65.536 * (exp(volume[1] * 0.0690876) - 1.0);

+		}else if(volfd >= 0){

+			if(write(volfd, r->ifcall.data, r->ifcall.count) < 0){

+				responderror(r);

+				return;

+			}

+		}else{

+			respond(r, "bad msg");

+			return;

+		}

+		respond(r, nil);

+		return;

+	}

+

 	p = (uchar*)r->ifcall.data;

 	n = r->ifcall.count;

 	r->ofcall.count = n;

@@ -313,17 +364,12 @@

 {

 	Stream *s;

-	if(r->fid->file == nil){

-		respond(r, "bug");

-		return;

-	}

-	if(strcmp(r->fid->file->name, "audio") == 0 && (s = r->fid->aux) != nil){

+	r->d.length = 0;

+	if(r->fid->file != nil && strcmp(r->fid->file->name, "audio") == 0 && (s = r->fid->aux) != nil){

 		qlock(s);

 		if(s->run){

 			r->d.length = (long)(s->wp - mixrp);

 			r->d.length *= NCHAN*2;

-		} else {

-			r->d.length = 0;

 		}

 		qunlock(s);

 	}

@@ -362,7 +408,7 @@

 void

 usage(void)

 {

-	fprint(2, "usage: %s [-D] [-s srvname] [-m mtpt]\n", argv0);

+	fprint(2, "usage: %s [-D] [-v] [-s srvname] [-m mtpt]\n", argv0);

 	exits("usage");

 }

@@ -370,7 +416,7 @@

 threadmain(int argc, char **argv)

 {

 	char *srv = nil;

-	char *mtpt = "/mnt/mix";

+	char *m, *mtpt = "/mnt/mix";

 	ARGBEGIN{

 	case 'D':

@@ -389,14 +435,23 @@

 	if(argc)

 		usage();

+	volfd = open("/dev/volume", ORDWR);

 	fs.tree = alloctree(nil, nil, DMDIR|0777, nil);

 	createfile(fs.tree->root, "audio", nil, 0666, nil);

+	createfile(fs.tree->root, "volume", nil, 0666, &volfd);

 	threadpostmountsrv(&fs, srv, mtpt, MREPL);

-	mtpt = smprint("%s/audio", mtpt);

-	if(bind(mtpt, "/dev/audio", MREPL) < 0)

+	m = smprint("%s/audio", mtpt);

+	if(bind(m, "/dev/audio", MREPL) < 0)

 		sysfatal("bind: %r");

-	free(mtpt);

+	free(m);

+

+	if(volfd >= 0){

+		m = smprint("%s/volume", mtpt);

+		if(bind(m, "/dev/volume", MREPL) < 0)

+			sysfatal("bind: %r");

+		free(m);

+	}

 	threadexits(0);

 }