linux-ext4 - Re: [PATCH] ext4: Add support for SFITRIM, an ioctl for secure FITRIM.

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Message-ID: <20140617124629.GA13868@thunk.org>
Date:	Tue, 17 Jun 2014 08:46:29 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	Dave Chinner <david@...morbit.com>, JP Abgrall <jpa@...gle.com>,
	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org,
	Geremy Condra <gcondra@...gle.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] ext4: Add support for SFITRIM, an ioctl for secure
 FITRIM.

On Tue, Jun 17, 2014 at 01:55:26PM +0200, Lukáš Czerner wrote:
> 
> I definitely agree with Dave here it is an ugly API hack. Fallocate
> seems much more suitable for this.
> 
> New flag FALLOC_FL_ISSUE_DISCARD which would work with
> FALLOC_FL_PUNCH_HOLE, FALLOC_FL_ZERO_RANGE and possibly
> FALLOC_FL_COLLAPSE_RANGE might actually be useful.

I agree it would be useful to have an FL_ISSUE_DISCARD (and while
we're at it, FL_ISSUE_SECDISCARD) as an fallocate flag.  That doesn't
obviate the usefulness of a BLKDISCARD ioctl for ext4 files, though.

Something else that might be useful, and perhaps more appropriate for
the Android use case, is to add a SECDISCARD flag to the unlinkat(2)
system call.  That way, people who want to do a "discard and then
unlink" don't have to be forced to do an open(2), fallocate(2),
close(2), and only *then* the unlink(2) system call.

Cheers,

						- Ted
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