[PATCH] dm-delay: Add a message to change delay

[Andy Grover <agrover@redhat.com>]

This enables runtime modification of the read and write delay values.

Make sure if the delay time is reduced to flush currently-delayed
bios first, to maintain ordering.

Signed-off-by: Andy Grover <agrover@redhat.com>
---
 Documentation/device-mapper/delay.txt |  8 +++++++
 drivers/md/dm-delay.c                 | 42 +++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/Documentation/device-mapper/delay.txt b/Documentation/device-mapper/delay.txt
index 15adc55..9e80751 100644
--- a/Documentation/device-mapper/delay.txt
+++ b/Documentation/device-mapper/delay.txt
@@ -10,6 +10,14 @@ Parameters:
 With separate write parameters, the first set is only used for reads.
 Delays are specified in milliseconds.
 
+Message Interface
+-----------------
+The delay target will accept a message of the following format:
+
+set_delay <read_delay> [<write_delay>]
+
+'man dmsetup' for more information on the message interface.
+
 Example scripts
 ===============
 [[
diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
index 57b6a19..04c2ab0 100644
--- a/drivers/md/dm-delay.c
+++ b/drivers/md/dm-delay.c
@@ -290,6 +290,47 @@ static int delay_map(struct dm_target *ti, struct bio *bio)
 	return delay_bio(dc, dc->read_delay, bio);
 }
 
+/* Message interface
+ *	set_delay <read_delay> [<write_delay>]
+*/
+static int delay_message(struct dm_target *ti, unsigned argc, char **argv)
+{
+	struct delay_c *dc = ti->private;
+	unsigned read_delay = dc->read_delay;
+	unsigned write_delay = dc->write_delay;
+	char dummy;
+
+	if (argc < 2 || argc > 3)
+		goto error;
+
+	if (strcasecmp(argv[0], "set_delay"))
+		goto error;
+
+	if (sscanf(argv[1], "%u%c", &read_delay, &dummy) != 1) {
+		ti->error = "Invalid read delay";
+		goto error;
+	}
+
+	if (argc == 3) {
+		if (sscanf(argv[2], "%u%c", &write_delay, &dummy) != 1) {
+			ti->error = "Invalid write delay";
+			goto error;
+		}
+	}
+
+	if (read_delay < dc->read_delay
+	    || write_delay < dc->write_delay)
+		flush_bios(flush_delayed_bios(dc, 1));
+
+	dc->read_delay = read_delay;
+	dc->write_delay = write_delay;
+	return 0;
+
+error:
+	DMWARN("unrecognised message received.");
+	return -EINVAL;
+}
+
 static void delay_status(struct dm_target *ti, status_type_t type,
 			 unsigned status_flags, char *result, unsigned maxlen)
 {
@@ -339,6 +380,7 @@ static struct target_type delay_target = {
 	.map	     = delay_map,
 	.presuspend  = delay_presuspend,
 	.resume	     = delay_resume,
+	.message     = delay_message,
 	.status	     = delay_status,
 	.iterate_devices = delay_iterate_devices,
 };
-- 
2.4.3