From af3cafd76c3f003b78babe051d768406da0afc1a Mon Sep 17 00:00:00 2001
From: Ian Lepore <ian@FreeBSD.org>
Date: Mon, 22 Dec 2014 22:07:22 +0000
Subject: [PATCH] Add a new loader(8) variable, twiddle_divisor, allowing
 control over the output frequency of the "twiddle" IO progress indicator. 
 The default value is 1.  For larger values N, the next stage of the animation
 is only output on every Nth call to the output routine.  A sufficiently large
 N effectively disables the animation completely.

---
 sys/boot/common/console.c  | 29 +++++++++++++++++++++++++++++
 sys/boot/common/loader.8   |  8 +++++++-
 sys/boot/forth/loader.conf |  1 +
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/sys/boot/common/console.c b/sys/boot/common/console.c
index 6c1fdab87f0c..6656eabf2a0a 100644
--- a/sys/boot/common/console.c
+++ b/sys/boot/common/console.c
@@ -39,6 +39,7 @@ static int	cons_set(struct env_var *ev, int flags, const void *value);
 static int	cons_find(const char *name);
 static int	cons_check(const char *string);
 static void	cons_change(const char *string);
+static int	twiddle_set(struct env_var *ev, int flags, const void *value);
 
 /*
  * Detect possible console(s) to use.  If preferred console(s) have been
@@ -52,6 +53,9 @@ cons_probe(void)
     int			active;
     char		*prefconsole;
     
+    /* We want a callback to install the new value when this var changes. */
+    env_setenv("twiddle_divisor", EV_VOLATILE, "1", twiddle_set, env_nounset);
+
     /* Do all console probes */
     for (cons = 0; consoles[cons] != NULL; cons++) {
 	consoles[cons]->c_flags = 0;
@@ -232,3 +236,28 @@ cons_change(const char *string)
 
     free(dup);
 }
+
+/*
+ * Change the twiddle divisor.
+ *
+ * The user can set the twiddle_divisor variable to directly control how fast
+ * the progress twiddle spins, useful for folks with slow serial consoles.  The
+ * code to monitor changes to the variable and propagate them to the twiddle
+ * routines has to live somewhere.  Twiddling is console-related so it's here.
+ */
+static int
+twiddle_set(struct env_var *ev, int flags, const void *value)
+{
+    u_long tdiv;
+    char * eptr;
+
+    tdiv = strtoul(value, &eptr, 0);
+    if (*(const char *)value == 0 || *eptr != 0) {
+	printf("invalid twiddle_divisor '%s'\n", (const char *)value);
+	return (CMD_ERROR);
+    }
+    twiddle_divisor((u_int)tdiv);
+    env_setenv(ev->ev_name, flags | EV_NOHOOK, value, NULL, NULL);
+
+    return(CMD_OK);
+}
diff --git a/sys/boot/common/loader.8 b/sys/boot/common/loader.8
index fe247ac89c58..cac56743a69f 100644
--- a/sys/boot/common/loader.8
+++ b/sys/boot/common/loader.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 1, 2013
+.Dd December 22, 2014
 .Dt LOADER 8
 .Os
 .Sh NAME
@@ -670,6 +670,12 @@ Overrides the compile-time set value of
 .Dv TCBHASHSIZE
 or the preset default of 512.
 Must be a power of 2.
+.It Va twiddle_divisor
+Throttles the output of the `twiddle' I/O progress indicator displayed
+while loading the kernel and modules.
+This is useful on slow serial consoles where the time spent waiting for
+these characters to be written can add up to many seconds.
+The default is 1 (full speed); a value of 2 spins half as fast, and so on.
 .It Va vm.kmem_size
 Sets the size of kernel memory (bytes).
 This overrides the value determined when the kernel was compiled.
diff --git a/sys/boot/forth/loader.conf b/sys/boot/forth/loader.conf
index bd7d296e9840..fd0b0de5fec2 100644
--- a/sys/boot/forth/loader.conf
+++ b/sys/boot/forth/loader.conf
@@ -75,6 +75,7 @@ module_path="/boot/modules"	# Set the module search path
 				# the block size is set to 512.  If the value
 				# is out of range ( < 8 || > 9008 ) an error is
 				# returned.
+#twiddle_divisor="1"		# >1 means slow down the progress indicator.
 
 
 ##############################################################