From bd04e1aef495761f5bc543f6fbc4857830566d0b Mon Sep 17 00:00:00 2001
From: Milan Broz <mbroz@redhat.com>
Date: Wed, 10 Aug 2011 09:13:33 +1000
Subject: [PATCH] If optional discard support in dm-crypt is enabled, discards
 requests bypass the crypt queue and blocks of the underlying device are
 discarded. For the read path, discarded blocks are handled the same as normal
 ciphertext blocks, thus decrypted.

So if the underlying device announces discarded regions return zeroes,
dm-crypt must disable this flag because after decryption there is just
random noise instead of zeroes.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
---
 drivers/md/dm-crypt.c         |  1 +
 drivers/md/dm-table.c         | 19 +++++++++++++++++++
 include/linux/device-mapper.h |  5 +++++
 3 files changed, 25 insertions(+)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 49da55c1528a..a9c709f193dc 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1698,6 +1698,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	}
 
 	ti->num_flush_requests = 1;
+	ti->discard_zeroes_data_unsupported = 1;
 	return 0;
 
 bad:
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 8b040f5c14f5..509bfe4b02f3 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1308,6 +1308,22 @@ static bool dm_table_is_nonrot(struct dm_table *t)
 	return 1;
 }
 
+static bool dm_table_discard_zeroes_data(struct dm_table *t)
+{
+	struct dm_target *ti;
+	unsigned i = 0;
+
+	/* Ensure that all targets supports discard_zeroes_data. */
+	while (i < dm_table_get_num_targets(t)) {
+		ti = dm_table_get_target(t, i++);
+
+		if (ti->discard_zeroes_data_unsupported)
+			return 0;
+	}
+
+	return 1;
+}
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			       struct queue_limits *limits)
 {
@@ -1335,6 +1351,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	else
 		queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
 
+	if (!dm_table_discard_zeroes_data(t))
+		q->limits.discard_zeroes_data = 0;
+
 	dm_table_set_integrity(t);
 
 	/*
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 3fa1f3d90ce0..99e3e50b5c57 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -197,6 +197,11 @@ struct dm_target {
 	 * whether or not its underlying devices have support.
 	 */
 	unsigned discards_supported:1;
+
+	/*
+	 * Set if this target does not return zeroes on discarded blocks.
+	 */
+	unsigned discard_zeroes_data_unsupported:1;
 };
 
 /* Each target can link one of these into the table */
-- 
2.39.5