From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: [PATCH] ext4: Add support for SFITRIM, an ioctl for secure FITRIM.
Date: Fri, 13 Jun 2014 14:57:19 -0500
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Cc: Dave Chinner <david@fromorbit.com>, linux-ext4@vger.kernel.org,
	Geremy Condra <gcondra@google.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
To: JP Abgrall <jpa@google.com>, "Theodore Ts'o" <tytso@mit.edu>
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On 6/13/14, 2:44 PM, JP Abgrall wrote:
> On Fri, Jun 13, 2014 at 7:31 AM, Theodore Ts'o <tytso@mit.edu> wrote:

<snip>

> 
>> If so, you might be better off either doing per-file encryption, or
>> per-file secure discard.
> 
> The per-file secure discard seems to be the way to go, as there are
> only a few places in Android where this needs to be turned on.
> The  current idletime-fstrim would  switch from FITRIM to SFITRIM to
> reduce the leftovers.

Apologies if this is a dumb thing to point out, but...
mmc is the only in-kernel driver (aside from xen) which can
even set the flags necessary to enable secure discard; and then
only if mmc_can_secure_erase_trim() is true, so it depends on
the card, I guess.

I don't know what device you're running on, but figured it might
be worth pointing out that not all hardware even supports this
capability.

-Eric