MFC r276079, r276087:

  Add a divisor parameter to twiddle() so that callers can request that
  output only happen on every Nth call.

  Add a new loader(8) variable, twiddle_divisor, allowing control over the
  output frequency of the "twiddle" IO progress indicator.

3 files changed, 37 insertions, 1 deletions

diff --git a/sys/boot/common/console.c b/sys/boot/common/console.c
index 6c1fdab..6656eab 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 fe247ac..cac5674 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 0e56ecc..8e06029 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.
 
 
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