1 files changed, 28 insertions, 0 deletions
diff --git a/sys/kern/subr_hints.c b/sys/kern/subr_hints.c
index f9085b2..08f8e8c 100644
--- a/sys/kern/subr_hints.c
+++ b/sys/kern/subr_hints.c
@@ -461,3 +461,31 @@ resource_disabled(const char *name, int unit)
 	       return (0);
 	return (value);
 }
+
+/*
+ * Clear a value associated with a device by removing it from
+ * the kernel environment.  This only removes a hint for an
+ * exact unit.
+ */
+int
+resource_unset_value(const char *name, int unit, const char *resname)
+{
+	char varname[128];
+	const char *retname, *retvalue;
+	int error, line;
+	size_t len;
+
+	line = 0;
+	error = resource_find(&line, NULL, name, &unit, resname, NULL,
+	    &retname, NULL, NULL, NULL, NULL, &retvalue);
+	if (error)
+		return (error);
+
+	retname -= strlen("hint.");
+	len = retvalue - retname - 1;
+	if (len > sizeof(varname) - 1)
+		return (ENAMETOOLONG);
+	memcpy(varname, retname, len);
+	varname[len] = '\0';
+	return (unsetenv(varname));
+}