mixer: remove volume backwards compat, add % interpretation

The current situation is fairly confusing, where an integer is interpreted
as a percent until you slap a decimal on it and magically it becomes an
absolute value.

Let's have a flag day in 14.0 and remove this shim entirely.  Setting with
percent can still be useful, so allow a trailing '%' to indicate as such.
As a side effect, we tighten down the format allowed in the volume a little
bit by ensuring there's no trailing garbage after the value once it's
separated into left and right components.

Reviewed by:	christos, hselasky, pauamma_gundo.com (manpages)
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D35101

2 files changed, 27 insertions, 15 deletions

diff --git a/usr.sbin/mixer/mixer.8 b/usr.sbin/mixer/mixer.8
index 284750538f7e..9a76cbe41f65 100644
--- a/usr.sbin/mixer/mixer.8
+++ b/usr.sbin/mixer/mixer.8
@@ -21,7 +21,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 20, 2022
+.Dd April 29, 2022
 .Dt MIXER 8
 .Os
 .Sh NAME
@@ -112,8 +112,8 @@ with one of the available devices):
 .It Sy Name Ta Sy Value
 .It Ar dev Cm .volume Ta Xo
 .Ar vol |
-.Oo Cm \&+ | Cm \&- Oc Ar lvol
-.Oo Cm \&: Oo Cm \&+ | Cm \&- Oc Ar rvol Oc
+.Oo Cm \&+ | Cm \&- Oc Ar lvol Oo % Oc
+.Oo Cm \&: Oo Cm \&+ | Cm \&- Oc Ar rvol Oo % Oc Oc
 .Xc
 .It Ar dev Cm .mute Ta Cm 0 | 1 | ^
 .It Ar dev Cm .recsrc Ta Cm ^ | + | - | =
@@ -128,16 +128,21 @@ The optional
 and/or
 .Ar rvol
 values have to be specified.
-The values have to be normalized 32-bit floats, from 0.0 to 1.0 inclusively.
-If no
-.Ql \&.
-character is present, the value is treated like a percentage, for backwards compatibility.
+The values should typically be decimal numbers between 0 and 1 with at most 2
+digits after the decimal point.
+A trailing percent sign indicates that the value should be treated as a
+percentage of 1.0, rather than an absolute value.
+Thus, 70% means the same as 0.7.
 If the left or right volume values are prefixed with
 .Cm +
 or
 .Cm - ,
 the value following will be used as a relative adjustment, modifying the
 current settings by the amount specified.
+Note that relative percentages are still relative to 1.0, not to the current
+value.
+If the volume is currently 0.40 and an adjustment of +20% is specified, then
+thet final volume will be set to 0.60.
 .Pp
 Volume can also be set using the shorthand
 .Ar dev Ns Cm =value .
diff --git a/usr.sbin/mixer/mixer.c b/usr.sbin/mixer/mixer.c
index c0a9ec25c6fa..e216efe3313c 100644
--- a/usr.sbin/mixer/mixer.c
+++ b/usr.sbin/mixer/mixer.c
@@ -341,7 +341,7 @@ mod_volume(struct mix_dev *d, void *p)
 	mix_ctl_t *cp;
 	mix_volume_t v;
 	const char *val;
-	char lstr[8], rstr[8];
+	char *endp, lstr[8], rstr[8];
 	float lprev, rprev, lrel, rrel;
 	int n;
 
@@ -356,25 +356,32 @@ mod_volume(struct mix_dev *d, void *p)
 	lrel = rrel = 0;
 	if (n > 0) {
 		if (*lstr == '+' || *lstr == '-')
-			lrel = rrel = 1;
-		v.left = strtof(lstr, NULL);
+			lrel = 1;
+		v.left = strtof(lstr, &endp);
+		if (*endp != '\0' && (*endp != '%' || *(endp + 1) != '\0')) {
+			warnx("invalid volume value: %s", lstr);
+			return (-1);
+		}
 
-		/* be backwards compatible */
-		if (strstr(lstr, ".") == NULL)
+		if (*endp == '%')
 			v.left /= 100.0f;
 	}
 	if (n > 1) {
 		if (*rstr == '+' || *rstr == '-')
 			rrel = 1;
-		v.right = strtof(rstr, NULL);
+		v.right = strtof(rstr, &endp);
+		if (*endp != '\0' && (*endp != '%' || *(endp + 1) != '\0')) {
+			warnx("invalid volume value: %s", rstr);
+			return (-1);
+		}
 
-		/* be backwards compatible */
-		if (strstr(rstr, ".") == NULL)
+		if (*endp == '%')
 			v.right /= 100.0f;
 	}
 	switch (n) {
 	case 1:
 		v.right = v.left; /* FALLTHROUGH */
+		rrel = lrel;
 	case 2:
 		if (lrel)
 			v.left += m->dev->vol.left;