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block: disable entropy contributions for nonrot devices

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Clear QUEUE_FLAG_ADD_RANDOM in all block drivers that set
QUEUE_FLAG_NONROT.

Historically, all block devices have automatically made entropy
contributions.  But as previously stated in commit e2e1a148 ("block: add
sysfs knob for turning off disk entropy contributions"):
    - On SSD disks, the completion times aren't as random as they
      are for rotational drives. So it's questionable whether they
      should contribute to the random pool in the first place.
    - Calling add_disk_randomness() has a lot of overhead.

There are more reliable sources for randomness than non-rotational block
devices.  From a security perspective it is better to err on the side of
caution than to allow entropy contributions from unreliable "random"
sources.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Mike Snitzer
2014-10-04 10:55:32 -06:00
committed by Jens Axboe
parent 7b7b7f7e02
commit b277da0a8a
14 changed files with 18 additions and 2 deletions
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drivers/block/nbd.c
+1
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@@ -847,6 +847,7 @@ static int __init nbd_init(void)
* Tell the block layer that we are not a rotational device
*/
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);
queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, disk->queue);
disk->queue->limits.discard_granularity = 512;
disk->queue->limits.max_discard_sectors = UINT_MAX;
disk->queue->limits.discard_zeroes_data = 0;