[ 047/108] dm table: clear add_random unless all devices have it set

Ben Hutchings
2012-10-07T23:30:43Z

From: Milan Broz <mbroz@redhat.com>

commit c3c4555edd10dbc0b388a0125b9c50de5e79af05 upstream.

Always clear QUEUE_FLAG_ADD_RANDOM if any underlying device does not
have it set. Otherwise devices with predictable characteristics may
contribute entropy.

QUEUE_FLAG_ADD_RANDOM specifies whether or not queue IO timings
contribute to the random pool.

For bio-based targets this flag is always 0 because such devices have no
real queue.

For request-based devices this flag was always set to 1 by default.

Now set it according to the flags on underlying devices. If there is at
least one device which should not contribute, set the flag to zero: If a
device, such as fast SSD storage, is not suitable for supplying entropy,
a request-based queue stacked over it will not be either.

Because the checking logic is exactly same as for the rotational flag,
share the iteration function with device_is_nonrot().

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/md/dm-table.c | 26 ++++++++++++++++++++++----
1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f900690..77b90ae 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1354,17 +1354,25 @@ static int device_is_nonrot(struct dm_target *ti, struct dm_dev *dev,
return q && blk_queue_nonrot(q);
}

-static bool dm_table_is_nonrot(struct dm_table *t)
+static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
+ sector_t start, sector_t len, void *data)
+{
+ struct request_queue *q = bdev_get_queue(dev->bdev);
+
+ return q && !blk_queue_add_random(q);
+}
+
+static bool dm_table_all_devices_attribute(struct dm_table *t,
+ iterate_devices_callout_fn func)
{
struct dm_target *ti;
unsigned i = 0;

- /* Ensure that all underlying device are non-rotational. */
while (i < dm_table_get_num_targets(t)) {
ti = dm_table_get_target(t, i++);

if (!ti->type->iterate_devices ||
- !ti->type->iterate_devices(ti, device_is_nonrot, NULL))
+ !ti->type->iterate_devices(ti, func, NULL))
return 0;
}

@@ -1396,7 +1404,8 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
if (!dm_table_discard_zeroes_data(t))
q->limits.discard_zeroes_data = 0;

- if (dm_table_is_nonrot(t))
+ /* Ensure that all underlying devices are non-rotational. */
+ if (dm_table_all_devices_attribute(t, device_is_nonrot))
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
else
queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
@@ -1404,6 +1413,15 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
dm_table_set_integrity(t);

/*
+ * Determine whether or not this queue's I/O timings contribute
+ * to the entropy pool, Only request-based targets use this.
+ * Clear QUEUE_FLAG_ADD_RANDOM if any underlying device does not
+ * have it set.
+ */
+ if (blk_queue_add_random(q) && dm_table_all_devices_attribute(t, device_is_not_random))
+ queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, q);
+
+ /*
* QUEUE_FLAG_STACKABLE must be set after all queue settings are
* visible to other CPUs because, once the flag is set, incoming bios
* are processed by request-based dm, which refers to the queue