Re: [PATCH] block: disable entropy contributions from nonrot devices

From: Jens Axboe
Date: Fri Oct 03 2014 - 17:18:14 EST


On 2014-10-02 18:11, Mike Snitzer wrote:
Introduce queue_flags_set_nonrot_clear_add_random() and convert all
block drivers that set QUEUE_FLAG_NONROT over to using it instead.

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.

Don't add a special function for this, just use the flag clear/set functions for both.

--
Jens Axboe

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