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

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Date:	Fri, 03 Oct 2014 15:17:56 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Mike Snitzer <snitzer@...hat.com>, linux-kernel@...r.kernel.org
CC:	tytso@....edu, gmazyland@...il.com, agk@...hat.com,
	mpatocka@...hat.com
Subject: Re: [PATCH] block: disable entropy contributions from nonrot devices

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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